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18 

 

 

 

Review 

Unlocking the potential of green hydrogen for a 

sustainable energy future: a review of production 

methods and challenges 
MD Farhan Imtiaz Chowdhury*, MD Fahim Sadat Bari, Muhaiminul Islam, Wasif Sadman Tanim, 

Redoy Masum Meraz 

Department of Mechanical Engineering, Chittagong University of Engineering and Technology, Bangladesh 

A R T I C L E   I N F O 
 

Article history: 
Received 10 June 2024  
Received in revised form 
12 July 2024 
Accepted 25 July 2024 
 
Keywords: 
Sustainable energy, Green hydrogen,  
Water electrolysis, Biomass gasification,  
Decarbonization 
 
*Corresponding author 
Email address:  
u1903002@student.cuet.ac.bd  

 
DOI: 10.55670/fpll.fuen.3.4.2 

A B S T R A C T 
 

The buzz around green hydrogen is growing louder as a game-changer in the 
fight for a clean and sustainable energy future. This article dives into the coolest 
ways to create this eco-friendly fuel, exploring methods like splitting water with 
electricity, turning plant matter into gas, and even some cutting-edge 
techniques in the pipeline. This research dives deep into the latest 
breakthroughs in electrocatalyst and electrode materials, the secret ingredients 
that could supercharge hydrogen production, making it cleaner and cheaper. 
While good old water electrolysis using alkaline and PEM electrolyzers is the 
current champ, it's still a bit pricey and not as efficient as we'd like. Thankfully, 
innovative ways to design these "fuel-splitting champions" and integrate them 
with renewable energy sources are showing promise as solutions. But green 
hydrogen isn't just some cool science experiment; it's a potential game-changer 
for cleaning up our transportation, factories, and even the way we power our 
homes, all to fight climate change. The study also identifies areas where we need 
more research and ironing out of kinks before widespread use. It emphasizes 
the importance of keeping the innovation train rolling, smart investments in 
this technology, and government policies that give it a green light. By pushing 
green hydrogen forward, we can slash greenhouse gasses, become more 
energy-independent, and finally build that sustainable energy future we've all 
been dreaming of! 
 

 
1. Introduction  

Our planet's running on fumes! We desperately need to 

eliminate dirty fuels like coal and gas, and luckily, there are 

some awesome alternatives on the horizon. Sunshine, wind, 

heat from the Earth's core, and even the power of moving 

water- these renewable sources hold immense promise (but 

they're not without their quirks) [1-2]. Enter hydrogen: this 

champion packs a serious energy punch, way more than other 

contenders, making it a strong candidate for the future of 

clean energy. It is also essential in significant quantities for 

hydroprocessing in petroleum refineries, cleaning natural 

gas, and upgrading biofuels. However, hydrogen gas is not 

naturally available on Earth and must be extracted from 

various resources like fossil fuels, organic materials, and 

water. Extracting hydrogen from these sources remains a 

prevalent but challenging task. Currently, most of the 

hydrogen we use comes from revamping natural gas, 

particularly methane. This process, known as steam methane 

reforming (SMR), is like breaking down natural gas molecules 

to get the hydrogen out. It's the most popular and affordable 

way to do this, and it is responsible for around half of all 

hydrogen production globally. In the US, SMR is the champion, 

churning out a whopping 95% of the country's hydrogen from 

natural gas [3-4]. Pretty much everyone agrees: our CO2 

emissions are climbing, fueled by a growing population and 

developing countries needing more energy. This is why 

there's a big push for sustainable energy sources, and guess 

what's getting a lot of buzz? Hydrogen. Some experts even 

think it could be the key to a future "hydrogen economy" [5]. 

The allure of hydrogen lies in its clean, burning nature- it 

creates no CO2 when used for power. But here's the catch: to 

get that hydrogen, we currently rely heavily on fossil fuels, 

which pump out tons of CO2 in the process. To cut these 

emissions, scientists are looking at ways to cook up hydrogen 

from renewable sources like plants and waste. They're 

experimenting with different methods, like superheating 

plant matter with water or turning plant-based fuels into 

hydrogen gas. This focus on bio-stuff for hydrogen production 

 

 

Future Energy 

Open Access Journal 

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November 2024| Volume 03 | Issue 04 | Pages 18-46 

Journal homepage: https://fupubco.com/fuen 

 
ISSN 2832-0328 

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MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

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is a win-win. It not only cleans things up, but the variety of 

plant sources available also makes our energy supplies more 

secure and boosts the economy in developing countries, 

which is a big deal [6]. A method for producing hydrogen 

without using fossil fuels is essential [7–10]. Fossil-free 

methods include photocatalysis, thermochemical water 

splitting, and electrolysis. Of these methods, only electrolysis 

in alkaline electrolyzers at moderate temperatures around 

75°C is commercially available. Although advanced in 

development, alkaline electrolysis requires an entirely 

electric energy input, which increases operating costs. Some 

of this electric energy can be replaced with cheaper thermal 

energy if electrolysis is conducted in solid oxide electrolyzers 

at temperatures between 500-1000°C. However, even at high 

temperatures, the proportion of energy that can be 

substituted with thermal energy is limited to less than 30%. 

Unlike electrolysis, thermochemical water-splitting 

processes use only thermal energy to split water and are 

theoretically highly efficient. Electrolyzers are classified into 

four main types: polymeric, alkaline, and solid oxide 

electrolyzers [11]. The process of direct water splitting by 

using sunlight is termed a photolytic process, which involves 

using light energy to separate water molecules into hydrogen 

and oxygen [12]. The replacement of fossil fuels with green 

hydrogen presents an effective means of alleviating the 

environmental impact attributed to energy-related 

industries, notably climate change, global warming, and acid 

rain. Green hydrogen is anticipated to exert a significant 

influence on forthcoming power and electricity systems and 

will be indispensable for cutting carbon emissions of energy-

intensive domains like transportation and buildings. 

Producing green hydrogen from renewable resources is key 

to promoting sustainable energy production. It holds the 

potential to meet the hydrogen demand of these sectors while 

yielding markedly reduced environmental effects compared 

to fossil fuels [13]. Countries worldwide want to decarbonize 

by 2050 to combat climate change, with green hydrogen 

playing a critical part. Green hydrogen, produced through 

water electrolysis, is essential for renewable energy power 

plants as well as a variety of industrial and transportation 

applications. This paper examines water electrolysis 

technologies, pricing, and current advancements in electrode 

materials and identifies research gaps and commercial 

electrolyzer limits. It also investigates hydrogen synthesis 

from ammonia breakdown with mixed metal oxide catalysts, 

addressing the issues of hydrogen storage and distribution. 

The review focuses on recent developments in 

electrocatalysts and electrolyzers, such as seawater 

electrolysis, as well as innovations in biomass steam 

gasification for hydrogen production, emphasizing the 

importance of renewable electricity in these processes. 

2. Water electrolysis  

Electrolysis of water is an electrochemical method for 

producing green hydrogen that uses power and produces no 

emissions. The following equation shows the fundamental 

reaction for water electrolysis. 

H2O + Electricity (237.2 kJ mol−1 ) + Heat (48.6 kJ mol−1 )= H2 

+ 0.5O2                                                                                                                                                     (1) 

The concept of dividing water into oxygen and hydrogen fuel 

is quite intriguing: in theory, it shouldn't take much zap 

(around 1.23 volts) to do the trick at room temperature. But 

in the real world, things get a bit trickier – we actually need a 

little more juice (around 1.48 volts) to overcome some 

roadblocks and inefficiencies in the process [14]. While 

scientists have known about water splitting for hundreds of 

years, making it affordable hasn't been easy. That's why, even 

today, only a small fraction (around 4%, or 65 million tons) of 

the world's hydrogen comes from this eco-friendly method. 

Most of the hydrogen we use is actually a leftover from a 

different industrial process [15] . The evolution of water 

electrolysis technologies boasts a rich history, dating back to 

the 18th century [16]. This continuous development has been 

driven by various trends, leading to roughly five distinct 

generations of the technology. Notably, this journey has 

witnessed the emergence of four key types differentiated by 

their electrolytes, operating conditions, and ionic agents 

(hydroxyl (OH-), proton (H+), and oxide (O2-): 

• Alkaline Water Electrolysis 

• AEM Water Electrolysis 

• PEM Water Electrolysis 

• Solid Oxide Water Electrolysis 

Despite these variations in the underlying mechanisms, the 

fundamental principle of water splitting remains consistent 

across all types [17]. 

2.1 Alkaline water electrolysis 

 Alkaline water electrolysis (Figure 1), a long-established 

and mature technology, is widely used for industrial 

hydrogen production. It has been operational since the late 

18th century, with significant advancements leading to the 

first large-scale plant in 1939. This process, which operates at 

temperatures between 30° and 80°C with a concentrated 

alkaline solution (5M KOH/NaOH), uses diaphragms made of 

asbestos and ZrO2 and electrodes made of stainless steel 

coated with nickel. Alkaline water electrolysis is not only a 

well-established technique that can reach multiple 

megawatts, but it is also economically viable for large-scale 

operations. It costs USD 500-1000/kW and boasts a system 

lifespan of 90,000 hours, making it a practical choice for 

industrial applications [18]. Despite its advantages, the 

technology faces limitations, such as low current densities 

(0.1–0.5 A/cm²) due to the moderate mobility of OH⁻ ions and 

the corrosive nature of KOH. The electrolyte’s sensitivity to 

CO₂ results in the formation of K₂CO₃, which clogs the anode, 

impeding ion transfer and reducing hydrogen production. 

Additionally, the system yields gases of lower purity (99.9%) 

because the diaphragm fails to entirely obstruct gas crossed-

over between the half-cells [18–22]. Many firms worldwide 

have successfully deployed and employed this technique for 

industrial applications. Nevertheless, there is a need for 

further advancements in this technology, including enhancing 

current density and minimizing gas crossover. New electrode 

materials and separators need to be developed to solve these 

problems. Additionally, integrating a renewable energy-

powered electrolyzer for acidic water (e.g. solar, wind) helps 

save capital costs. Some research institutes and organizations 

are still attempting to improve efficiency and reduce 

hydrogen production costs. By development of low-cost and 

noble metal-free MoS2@Ni0.96S as a heterojunction hybrid 

mailto:MoS2@Ni0.96S
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MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

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Electrodes designed for the hydrogen evolution reaction 

(HER) and oxygen evolution reaction (OER) in alkaline 

surroundings. MoS2@Ni0.96S-1. The electrocatalyst 

demonstrated the most significant response, with a 

considerably lower overpotential of 104 mV at 10 mAcm−2, in 

contrast to the overpotential of 182 mV for both the HER and 

OER at the same temperature. Additionally, obtained a lower 

cell voltage of 1.86V to separate water in the aggregate and 

displayed greater stability during 15 hours of nonstop 

operation [23]. The improvement of this material is 

attributed to the numerous heterojunction interfaces present 

within it, the increased exposure of active sites, and the strong 

integration between ultrathin MoS₂ nanosheets and non-

stoichiometric Ni₀.₉₆S nanocrystals MoS₂@Ni₀.₉₆S-1h [24]. 

Researchers have created a bifunctional electrocatalyst in 

nanostructure, NiCo-NiCoO₂@Cu₂O@CF, designed for overall 

water splitting and evaluated its performance in a 1M KOH 

mixture. This electrocatalyst exhibited enhanced 

electrochemical performance for both the hydrogen evolution 

reaction (HER) and the oxygen evolution reaction (OER) in 

alkaline media, with low overpotentials of 133 mV and 327 

mV, respectively, to achieve a current density of 10 mA cm². 

It also showed small Tafel slopes of 119 mV dec⁻¹ for HER and 

118 mV dec⁻¹ for OER. The electrocatalyst's effectiveness was 

further confirmed through single-cell electrolysis, where it 

achieved a cell voltage of 1.69 V at a current density of ≥10 

mA cm⁻². It remained stable for 12 hours of continuous 

electrolysis within a very acidic solution due to the strong 

physical cling of NiCo-NiCoO₂ nanoparticles. The enhanced 

efficiency is attributed to the compact dimensions and even 

spread of the nano heterostructures across the surface of the 

copper foam after oxidation. This facilitated optimal 

utilization of active sites during electrochemical reactions 

[25]. Researchers created a very effective bifunctional 

electrocatalyst using NiCoP nanoflakes (NiCo(nf)-P) derived 

from the 2D metal-organic framework (MOF) for overall 

water splitting in alkaline conditions. 

 

They assessed its functionality by employing a three-

electrode cell configuration and conducting linear sweep 

voltammetry (LSV) with a cycling rate of 2 mV s⁻¹ in a 1M KOH 

solution. The electrocatalyst NiCo(nf)-P exhibited excellent 

electrocatalytic performance, with a lower onset mili-voltage 

of 37 mV for the hydrogen evolution reaction and 1.435 V for 

the oxygen evolution reaction at a current density of 100 mA 

cm⁻², outperforming the commercial 5% Pt/C (43 mV) and 

IrO₂ (1.504V). Furthermore, NiCo(nf)-P had low overpotentials 

of 0.119V for HER and 0.315V for OER, compared to 291 mV 

for Pt/C and 400 mV for IrO₂, to achieve a current density of 

100 mA cm⁻². The Tafel slopes were also much lesser for 

NiCo(nf)-P (0.112V dec⁻¹ for HER and 0.066V dec⁻¹ for OER) 

than for Pt/C (164 mV dec⁻¹) and IrO₂ (88 mV dec⁻¹), 

indicating efficient Electric current flow at the surfaces of 

electrocatalytic materials. Furthermore, the stability of the 

developed NiCo(nf)-P electrocatalyst was tested at various 

current densities (100, 500, and 1000 mA cm⁻²) for both. 

Through chronopotentiometric (V-t) measurements of 

continuous operation, the data indicated consistent 

electrochemical performance over a 30-hour period for both 

HER and OER, as depicted in Figure 2.  This study involved the 

synthesis of a carbon-supported Ni-Mo-O/Ni₄Mo 

electrocatalyst having nanointerface doped-up with N (Ni-

Mo-O/Ni₄Mo@NC) using calcination and electrodeposition 

methods. The electrocatalysis performance of this catalyst for 

an evolutionary process using hydrogen in a 1M KOH alkaline 

solution was thoroughly evaluated. The Ni-Mo-O/Ni₄Mo@NC 

electrocatalyst unequivocally demonstrated remarkable 

electrocatalytic activity, exhibiting a significantly lower over-

potential of 61(mV) at a current density of 10 mA cm⁻². This 

astounding performance, 50% lower than that of Ni-Mo-O 

(0.120V), can be attributed to the N-doped layers of Carbon. 

Under neutral conditions in a 1M PBS solution, Ni-Mo-

O/Ni₄Mo@NC exhibited an overpotential of less than 60 mV, 

while Ni-Mo-O showed an overpotential of around 100 mV.  

 

 
Figure 1. Diagram depicting the working principle of alkaline water electrolysis [24] 

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MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

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The Tafel slope for Ni-Mo-O/Ni₄Mo@NC was 0.099V dec⁻¹, 

which is less than the Tafel slope of Ni-Mo-O, which was 135 

mV dec⁻¹ [26]. Creating an efficient HER electrocatalyst, 

Co₂P/N@Ti₃C₂Tx@NF, with 3-dimensional porous 

architectures and interactions between heterostructures. 

They utilized a process that included nitriding and 

electrodeposition in two steps on MXene-modified NF. This 

electrocatalyst performed well in 1M KOH solution, with an 

excessive potential of 15 mV at 10 mA cm⁻² and a Tafel incline 

of 0.030V dec⁻¹. It also remained stable after 3000 CV cycles. 

DFT simulations revealed significant binding energy (−0.822 

eV) and ideal hydrogen adsorption energy, showing its 

potential as an effective electrocatalyst for HER [27]. 

2.2 Anion exchange membrane (AEM) water electrolysis 

AEM water electrolysis is an emerging method for 

producing green hydrogen. AEMWE is gaining popularity 

among research organizations and institutions due to its low 

cost and superior performance compared to traditional 

electrolysis technologies.  

 

 

 

 

 

 

 

 

 

 

We and Scott published the first scholarly article on 

AEMWE in 2011. Since then, several researchers have 

contributed to its advancement [28]. AEM water electrolysis 

technology is comparable to traditional alkaline water 

electrolysis [29]. Alkaline water electrolysis differs from AEM 

water electrolysis in that it replaces traditional asbestos 

diaphragms with quaternary ammonium ion exchange 

membranes. AEM water electrolysis has various advantages, 

including using cost-effective transition metal catalysts 

instead of noble metal catalysts and using purified water or a 

low-concentration alkaline solution (1M KOH) as the 

electrolyte instead of a high-concentration solution (5 KOH 

Solution) [30]. AEM water electrolysis utilizes an anion 

exchange membrane and electricity to split water through 

electrochemical reactions. The process involves two main 

reactions: the hydrogen evolution reaction (HER) and the 

oxygen evolution reaction (OER). At the cathode, water 

molecules are reduced to produce hydrogen gas (H₂) and 

hydroxyl ions (OH⁻) by gaining electrons. Hydrogen is 

released at the cathode, while OH⁻ ions move across the 

membrane towards the anode, attracted by its positive 

Figure 2. The electrocatalytic activity of the following synthesized electrocatalysts will be evaluated: LDH(NS), NiCo(NS)-P, MOF(nf), NiCo(nf)-P, 

NiCo(NR)-P, as well as the commercial 5% Pt/C and IrO2.(a) Polarization curves for the hydrogen evolution reaction (HER), (b) HER potential 

failures at varying current densities of 100, 500, and 1000 mAcm−2, (c) Tafel slopes for the HER, (d) Polarization curves for the oxygen evolution 

reaction (OER), (e) Different current densities of 100, 500, and 1000 mA cm−2 used to measure OER overpotentials.(f) Tafel incline for the OER, 

(g, h) Stability studies (V-t curves) of the NiCo(nf)-P electrocatalyst for both HER and OER at current densities of 100, 500, and 1000 mA cm−2,(i) 

Polarization curves of NiCo(nf)-P and NiCo(nf)-P; Commercial IrO2 and 5% Pt/C for overall water splitting. The inset shows the V-t curves of 

NiCo(nf)-P at the specified current densities for the overall water splitting process [25]. 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

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charge. Simultaneously, electrons flow through an external 

circuit to the anode. At the anode, OH⁻ ions recombine to form 

water and oxygen gas (O₂), which is released. This describes 

the fundamental operation and half-cell reactions involved in 

AEM water electrolysis Figure 3. 

Significant advances and challenges characterize the 

field of AEM water electrolysis. The technology is currently in 

the developmental stage, steadily progressing towards kW-

scale applications. Many international research organizations 

and institutions are currently engaged in the advancement of 

AEM water electrolyzers, as outlined in Table 1. However, 

substantial advancements and enhancements are necessary 

to expand the utilization of this technology for business 

purposes. Key challenges include achieving sufficient 

stability, with current targets aiming for operational lifetimes 

of up to 100,000 hours, and reducing the high cost of 

hydrogen production. As of 2020, the production cost was 

approximately USD 1279 per kW/H₂, with a target of reducing 

this cost to USD ≤ 300 per kW/H₂ by 2050. Recent progress 

has been achieved in tackling these obstacles, including the 

creation of a 3D electrode for producing oxygen using non-

crystalline NiFeOOH on activated carbon fiber paper. This 

electrode showed excellent electrochemical performance in a 

1M KOH solution, with an overpotential of just 170 mV at 10 

mA cm⁻², a low Tafel slope of 39 mV dec⁻¹, and exceptional 

stability over 240 hours of continuous operation. Synthesis 

report of Cu-Co-P on carbon paper via electrodeposition 

techniques optimized for HER in alkaline solutions and 

enhancement of electrochemical performance through 

surface modification and copper (Cu) incorporation. The 

modified Cu-Co-P1200/CP electrode demonstrated 

significant enhancements, having an excessive potential of 59 

mV at 0.010A cm⁻² and a Tafel incline of 0.038V dec⁻¹ 

presented in Figure 4. This electrode also demonstrated 

promising performance in a single-cell AEM water 

electrolyzer setup. Additionally, the development of a non-

noble metal Electrocatalyst Cu₀.₅Co₂.₅O₂ anodes by means of 

co-precipitation techniques showed improved performance 

with an overpotential of 285 mV at 10 mA cm⁻² in 1M KOH 

solution.  

 

This electrode maintained high stability during extended 

operation, including achieving a current density of 1.3 A cm⁻² 

at 1.8 V and demonstrating durability over 2000 hours at 10 

mA cm⁻². Furthermore, advancements in poly (fluorenyl-co-

aryl piperidinium) (PFAP)-based anion exchange materials as 

electrolytes and binders have contributed to achieving high 

ionic conductivity and durability under alkaline conditions. 

Combined with platinum group metal (PGM) catalysts, these 

materials achieved impressive cell performances and 

durability, highlighting their potential for practical 

applications in AEM water electrolysis. Overall, while 

significant progress has been made in improving the 

performance and durability of AEM water electrolysis 

technologies, ongoing research and development efforts are 

essential to overcome remaining challenges and 

commercialize this technology effectively [32–35]. 

2.3 PEM water electrolysis  

In PEM water electrolysis, water undergoes 

electrochemical splitting into hydrogen and oxygen. Initially, 

at the anode, water molecules decompose to produce oxygen 

(O₂), protons (H⁺), and electrons (e⁻). Oxygen is released from 

the anode surface, while protons migrate through the proton-

conducting membrane to the cathode. Simultaneously, 

electrons flow through an external circuit to the cathode. At 

the cathode, protons and electrons combine to form hydrogen 

gas (H₂). This process outlines the fundamental principle of 

PEM water electrolysis, as depicted in Figure 5. PEM water 

electrolysis technology has achieved a high level of technical 

maturity and is currently available for industrial and 

transportation applications on the megawatt (MW) scale. This 

is facilitated by several prominent manufacturers, as 

indicated in Table 1. Further enhancements are required to 

effectively lower the cost of hydrogen production, which 

currently ranges from USD 700 to 1400 per kW/H₂ (2020), 

with a targeted reduction to USD ≤ 200 per kW/H₂ by 2050. 

Challenges include replacing or reducing platinum group 

metals, minimizing costs associated with bipolar plate 

coatings, and optimizing membrane thickness to enhance cell 

efficiency (Figure 6). 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3. Schematic representation of the working principle of AEM water electrolysis electrolysis [31] 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

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Figure 4. a) The HER diagrams depicting polarization of Cu-Co-P1200/CP electrodes were rigorously tested with varying concentrations of Cu2+ in 

a 1M KOH sol. at a scanned rate of 0.005V/s. b) Investigating the impact of changing Cu2+ concentrations on overpotential while upholding a constant 

current density of 10 mA/cm2. c) Tafel slopes. d) Current-Voltage polarization curves of a single cell AEM water electrolyzer with IrO2/CP as the 

anode, paired with the as-synthesized Cu10-Co-P1200/CP electrode as the cathode, and a comparison with the commercial Pt/C/CP [32]. 

Figure 5. Schematic illustration of the PEM water electrolysis operating principle [31] 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

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Efforts towards cost reduction include innovative approaches 

such as integrated electrode architectures. For instance, 

integrated Pt nanowires on ultrathin titanium gas diffusion 

layers (PtNW/Ti) have demonstrated promising performance 

in PEM water electrolyzers, achieving a lower overpotential 

of 63 mV at 100 mA cm⁻² and a cell voltage of 1.643 V at 1 A 

cm⁻² with significantly reduced catalyst loadings compared to 

conventional MEAs. Additionally, synthesized ionomer-free 

electrodes (1T-2H MoS₂NS/CFP) for hydrogen evolution, 

showing a minimal overpotential of 192 mV and a cell voltage 

of 2.25 V at 2 A/cm² in PEM water electrolyzers. Despite 

commercial Pt/C catalysts exhibiting slightly lower cell 

voltages (2.18 V), the performance of these integrated 

electrodes represents a notable advancement over non-noble 

catalysts. These innovations underscore ongoing efforts to 

enhance the efficiency and cost-effectiveness of PEM water 

electrolysis technologies for broader market adoption [37]. 

2.4 Solid oxide water electrolysis 

 Solid oxide water electrolysis typically operates at 

elevated temperatures, utilizing water in the form of steam to 

produce green hydrogen and oxygen. During the process, at 

the cathode, water molecules are initially reduced to 

hydrogen (H₂) and oxide ions (O₂⁻) through the addition of 

two electrons. Hydrogen is released from the cathode, while 

oxide ions migrate through an ion exchange membrane to the 

anode. At the anode, oxide ions undergo further reduction to 

produce oxygen and electrons.  

 

 

 

 

 

Oxygen is then released from the anode, and electrons 

travel back to the cathode through an external circuit due to 

the positive charge attraction. This outlines the fundamental 

operational principle of solid oxide water electrolysis, 

depicted in Figure 7. Solid oxide water electrolysis technology 

is currently advancing towards commercialization, with 

various global research institutions and organizations 

actively involved in its development. Several commercial 

manufacturers of solid oxide electrolyzers are listed in Table 

1. This technology offers high energy efficiency by operating 

at elevated temperatures and utilizing non-noble metal 

electrocatalysts. However, challenges such as long-term 

stability and high hydrogen production costs remain 

significant. Presently, stability is around 20,000 hours, with a 

targeted improvement to 100,000 hours, while the current 

hydrogen production cost stands at USD 2000 per kW/H₂ 

(2020), with a goal to reduce it to USD ≤ 200 per kW/H₂ by 

2050.To address these challenges, efforts are focused on 

enhancing long-term stability through electrochemical 

fluctuations of electrode materials and exploring new 

perovskite materials for improved durability. Additionally, 

scaling up electrolyzer production with renewable energy 

sources is being pursued to reduce costs. Recent 

advancements include the development of Ni1−xCdxO-SDC 

composite oxide materials for hydrogen electrodes in 

reversible solid oxide cells. Their R-Ni0.9Cd0.1O-SDC electrode 

exhibited high electrocatalytic activity and stability under 

various conditions (Figure 8 and Figure 9).  

Figure 6. This is a graphical illustration of an electrolyte without ionomers featuring ultra-low-loading, defect-rich 1T-2H MoS2 nanosheets 

synthesized in situ. The HAADF-STEM visuals in (a–f) confirm the presence of boundaries, fissures, and atomic holes simultaneously in defect-rich 

1T-2H MoS2NS/CFP. The polarization curves of MoS2 assemblies/CFP and 1T-2H MoS2NS/CFP with defects are displayed in (g), along with the 

corresponding Tafel plots in (h). Moreover, (i) demonstrates the polarization curves of defected 1T-2H MoS2NS/CFP and MoS2 assemblies/CFP in 

a PEMEC at 353K [36]. 



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Figure 7. Schematic view of solid oxide water electrolysis working principle [31] 

Figure 8. Physicochemical and electrochemical performance of the developed IrRu@WO3 nanorods.(a) The diagram shows the synthesis procedure 

of IrRu@WO3. (b) The left image is a scanning electron microscope (SEM) image, and the right image shows a sectional view of the array. (c) A 

transmission electron microscope (TEM) image displays a single nanorod.(d) A high-resolution TEM (HR-TEM) image demonstrates the IrRu 

coating, with blue indicating Ru and purple indicating Ir. Inset images provide magnified views of specific areas. (e) A selected area electron 

diffraction image is displayed. (f) A scanning TEM (STEM) image illustrates a single nanorod with overlapping element mapping. (g) A high-angle 

annular dark-field (HAADF)-STEM image displays an IrRu grain. Elemental mapping of Ir, Ru, W, and O is presented, along with a merged picture 

and scanning lines parallel to the pink line. (h) CV curves are included, with a darked/marked area representing the OER stabilities.(i) OER LSV 

curves are shown. (j) I-V polarization curves for a single electrolyzer at 353K are displayed. (k) Durability testing at 353K at same current density 

is also included [37]. (To understand the color references in the figure legend, please consult the online version of the article.) 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

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Figure 9. (a) Patterns from XRD analysis; (b) Images from TEM and HRTEM; (c, d) Patterns from corresponding Fourier transforms of IrO2; (f) 

Images from TEM and HRTEM; (h) Images from HAADF; and the corresponding mapping of Ir, O, C, and N elements in IrO2/CN; (i) Images from TEM 

and HRTEM; (k) Images from HAADF; and the corresponding EDX mapping of Ir, O, C, and N elements in IrO2/N-CN. (l) I-V polarization curves, (m) 

IrO2/N-CN stability over 300 hours at 1.6 A cm2, and (n) IrO2, IrO2/CN, and IrO2/N-CN mass and specific activities at 12.48 V [38] 

Table 1. Global main electrolyzer manufacturers and their specifications 

Alkaline Water Electrolysis  
Manufactured by Origin of Country Generic Name H2 Capacity (m3/h) Pressure (psi) Energy used 

(kWh/Nm3) 
Ref. 

Nel. Norway A3880 2784–4500.8 2900.75 3.8–4.4 [39] 
Cummins Canada HySTATÂ® -100–10 116 145.038 5.0–5.4 [31] 
John Cockerill Belgium DQ-500 580 435.113 4.0–4.3 [31] 
McPhy France MeLyzer 800–30 928 435.113 4.5 [40] 
Sunfire Germany HyLink Alkaline 2586.8 435.113 4.7 [41] 
Nuberg PERIC China–India ZDQ-600 696 290.075 4.6 [42] 
TIANJIN Mainland China FDQ800 1160 72.5189 4.4 [35] 
GreenHydrogen Denmark HyProvide A-90 104.4 507.632 4.3 [43] 
AEM Water Electrolysis 
Enapter Germany AEM Multicore 210 35 4.8 [44] 
PEM water electrolysis 
Nel. Norway M5000 5800 435.113 4.5 [45] 
Cummins Canada HyLYZERÂ® -4.000-30 4640 435.113 4.3 [31] 
Siemens Germany Silyzer 300 116–2320 507.632 N/A [46] 
Proton onsite USA M400  483.72 435.113 N/A [47] 
ITM Power UK HGASXMW 127.6–2204 290.075 N/A [48] 
Plug Power USA GenFuel 5 MW 1160 580.151 5.2 [31] 
Elogen France ELYTE 260 301.6 435.113 4.9 [49] 
Solid oxide water electrolysis 
Sunfire Germany HyLink SOEC 870 580.151 3.6 [41] 

 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

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Introduction of cobalt-free Ba1−xNdxFeO3−δ perovskite 

materials as oxygen electrodes in solid oxide cells, 

demonstrating high electronic conductivity and low thermal 

expansion coefficients, along with significant current 

densities at high temperatures. These developments 

underscore ongoing efforts to improve the efficiency, 

stability, and cost-effectiveness of solid oxide water 

electrolysis technology for broader commercial applications 

[50–52]. 

2.5 Biomass gasification 

Hydrogen can be produced through various methods, as 

illustrated in Figure 10. These methods include 

thermochemical processes, which require heat, organic 

reactants like water or ammonia, and fossil fuels to be 

effective [53]. The biological technique uses microbes 

(bacteria and microalgae) to convert biomass into hydrogen 

through a biological reaction [55]. Sunlight or organic 

molecules serve as the activator for this approach. Two 

biological processing technologies, microbial biomass 

conversion (MBC) and photobiological techniques, are 

employed to produce hydrogen. The most common method 

for producing hydrogen is through electrolysis using 

electricity, assuming the electricity comes from zero-carbon 

sources such as solar and photovoltaic energy [50,56–59]. 

Variable electricity generation from sources such as solar and 

photovoltaics is insufficient to guarantee a consistent 

hydrogen supply.  Consistent production methods, which are 

currently reliant on fossil fuels, need to be supplemented. 

Utilizing established technologies, biomass energy has the 

potential to play a significant role in producing energy 

carriers like biomethane or syngas, which can be converted 

into hydrogen as required. There is a wealth of scientific 

literature [60–65], which showcases the different methods of 

converting biomass into hydrogen, which can be categorized 

into two main groups. These processes involve biochemical 

reactions driven by microorganisms and photo-fermentation, 

as well as thermochemical reactions like pyrolysis & 

gasification. After that, the subsequent procedures involve 

syngas upgrading and biomethane reforming. In order to 

generate a gas that contains a high proportion of hydrogen 

and minimal carbon content, it is essential to utilize a 

hydrogenizer to alter the hydrogen-rich syngas. This process 

involves reducing the carbon monoxide (CO) content by 

converting it into carbon dioxide (CO₂) and hydrogen (H₂), 

and then eliminating the CO₂. 

 

 

 

 

 

 

 

 

 

Figure 10. Production methods of hydrogen [54] 

Specialized water-shift reactors with steam injection that 

are pressurized and CO₂ removal systems can be employed to 

effectively eliminate the carbon content  [66]. 

2.6 Experimental gasification plant 

An early version of the gasifier, designed for the process 

of converting a substance into gas using air, was adapted for 

oxy-gasification experiments, requiring technical and 

mechanical modifications to the feed framework, piping, and 

gasification agent allocation to guarantee consistent reaction 

conditions (Figure 11). Special attention was given to sealing 

the gasifier to prevent air infiltration during the oxy-steam 

gasification process, which operates at higher temperatures. 

Oxygen was kept in pressurized tanks at 200 bars for 

gasification, while a small electric boiler produced saturated 

steam at 4 bars, with a capacity of up to 10 kg/h. The process 

line had different meters and sensors to control and oversee 

the conditions during experiments. The gasifier functions in a 

semi-batch manner, where biomass is held in a tightly sealed 

container, allowing for around 8 hours of self-sufficiency. The 

biomass is transported into the reactor by a screw conveyor 

in an automated manner. Upon ignition with a removable 

external heater, the process becomes auto-thermal. The 

gasifier is maintained at near-atmospheric pressure by a 

blower and oxygen supply, with downstream sections at 

slightly lower pressure to prevent air leakage. A mobile 

scraper is used to frequently clean the grate supporting the 

reaction bed in order to avoid the accumulation of char along 

with ash. The system for removing impurities from syngas 

consists of three cyclones in a row and a filter made of 

biomass and fabric. After the experiment, the ash is kept in a 

sealed tank for later removal. An Agilent 3000 micro-gas 

chromatograph is used to constantly check the composition 

within the syngas. It measures significant elements like CO, 

CO2, H2, CH4, N2, O2, and other hydrocarbons. This allows for 

ongoing evaluation of the gasification process. Analysis of tar 

and solid particles is conducted once the operating conditions 

become stable, following the guidelines outlined in CEN/TS 

15439:2006. The facility is outfitted with an electronic system 

that gathers data to oversee and document the primary 

operational variables, such as temperatures, pressures along 

with syngas flow. This ensures accurate control and 

assessment of the gasification process [67,68]. 

 

 

 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

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3. Hydrogen generation from syngas evaluation of 

effectiveness 

 Enhancing the level of hydrogen concentration in syngas 

generated by oxy-steam gasification can reduce its carbon 

content. A hydrogenation plant capable of producing large 

amounts of H2 and CO2 gases and the system was constructed 

and tested using the Aspen Plus® tool.  The hydrogenizer, 

depicted in Figure 12a, relies on syngas generated from the 

oxy-steam gasification process.  To lower CO content, we 

employed a straightforward configuration with a single 

water-shift. To reduce the amount of steam used and 

minimize its effect on the energy requirements of the 

hydrogenizer, the method employs absorption using a heated 

potassium carbonate solution to remove CO2.   This method is 

chosen for its well-established efficiency in CO2 removal; the 

off-gas experiences low hydrogen loss, and the rich solution 

requires modest heat for regeneration. The hydrogenizer 

efficiently recovers sensible heat from several streams to 

improve energy sustainability [69]. 

3.1 Configuration of the plant 

 The plant operates by first cooling high-temperature 

syngas to 300°C to prevent TAR condensation, producing 

some steam in the process. The resulting syngas is 

subsequently cooled to the surrounding temperature by 

employing a water-based scrubber, which eliminates small 

particles and condensable TAR. The treated water is utilized 

on steam generators downstream. A portion of the purified 

syngas is directed towards a boiler in order to provide the 

steam required for the complete gasification and hydrogen 

production facility. A three-way modulating valve ensures the 

correct amount of syngas is sent to the boiler, making the 

system self-sufficient and not reliant on external energy 

sources. The carbon dioxide emissions resulting from this 

technique are deemed to be carbon neutral  due to the bio-

origin of the syngas. The remaining syngas is used for 

hydrogen production. Operating at 3.9 bar, prior to entering 

the CO-Shift catalytic reactor, the syngas undergoes 

compression and is combined with steam, where CO reacts 

with steam to produce CO2 and H2.  

 

 

The mixture needs to enter the reactor at 320°C, so it is 

preheated using a heat regenerator that recovers heat from 

the reactor's exothermic reaction. The reaction that occurs is, 

CO(g) +H2O(g) → CO2(g) +H2(g)          (2) 
The gas produced by the CO-Shift reactor contains a 
significant amount of CO2, which is captured using a hot 
potassium carbonate solution. This process involves an 
absorber to separate CO2, a heat exchanger for heat recovery 
between lean and rich solvents, and a heat exchanger is used 
to recycle heat within lean and rich solvents, while a stripper 
is employed to extract carbon dioxide (CO2) from the rich 
solution by utilizing heat from medium-pressure steam 
condensation. The reaction taking place for CO2 capture, 

CO2(g) +K2CO3(aq) +H2O(l) → 2 KHCO3(aq)         (3) 
The plant requires a significant amount of steam for various 
processes: in order to make gas with oxygen in the 
gasification process, to keep the exact molar ratio of steam to 
carbon in the CO-Shift reactor, and to strip CO2 in the reboiler. 
To ensure the system's independence from external energy 
sources and to maintain the renewable origin of the hydrogen, 
part of the syngas is used to meet the thermal power demand. 
A syngas cooler located downstream of the gasifier is 
responsible for the production of steam and additional steam 
is generated in a syngas-fired boiler, ensuring the hydrogen 
production system is energetically autonomous. 

3.2 Photocatalytic water splitting 

Photocatalysis, sometimes termed artificial 

photosynthesis because it mimics the process of 

photosynthesis in plants, involves enhancing or altering the 

rate of redox reactions with the help of solar energy and a 

stable semiconductor that remains unaffected and 

unconsumed during the reaction [70]. The core of 

photocatalytic hydrogen production is a semiconductor 

photocatalyst capable of converting solar energy into 

chemical energy. Ideal photocatalysts should be efficient, 

affordable, recyclable, and non-toxic, with proper band 

alignment and bandgap. When these criteria are met, the 

photocatalyst can generate excitons that participate in redox 

reactions to split water into hydrogen and oxygen.  

Figure 11. Diagram illustrating the flow of the experimental gasification plant [54] 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

29 

 

 

 

 

 

 

 

 

 

 

 

Figure 12. a) Aspen Plus process flow diagram; b) process flow diagram for the hydrogenation of syngas plant [54]  (The reader is suggested to 

use the referred paper for a better view of the image). 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

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The fundamental steps in photocatalytic water splitting 

to produce hydrogen fuel are illustrated in Figure 13. When a 

photocatalyst is exposed to solar energy equal to its bandgap, 

it generates charge carriers (electrons and holes). Electrons 

move to the conduction band, while holes stay in the valence 

band.  

 

Figure 13. Illustration of the fundamental steps in the process of 

photocatalytic hydrogen production [71] 

These carriers then reach the surface and engage in 

redox reactions, producing hydrogen and oxygen. This rapid 

water-splitting process occurs in nanoseconds to 

microseconds and competes with charge recombination. It 

involves two half-reactions: hydrogen evolution (HER) and 

oxygen evolution (OER), which together make up the overall 

water splitting reaction (OWR). These reactions are given 

below one by one [70], 

HER: 4H+ + 4e- = 2H2 

OER: 2H2O = 4H+ + 4e- + O2 

OWR: 2H2O = 2H2 + O2 

When energetic photons are absorbed, they generate and 

separate charge carriers. The holes in the valence band split 

water molecules into protons and oxygen gas, as described by 

the second reaction. These protons then react with the free 

electrons in the conduction band to produce hydrogen gas, as 

shown in the first reaction. 

4. Methane pyrolysis 

 Methane pyrolysis offers a way to produce COx-free hydrogen 

through an endothermic reaction: 

CH4(g) = C(s)+2H2(g), ΔH(1000K)=89.8kJ mol        (4) 

Noncatalytic methane pyrolysis requires very high 

temperatures, around 1300°C, to decompose methane 

effectively and achieve high hydrogen selectivity, which is 

impractical for industrial use. Therefore, research has focused 

on two main areas to commercialize this process: 

1. Developing commercially viable catalysts to lower the 

reaction temperature and enhance methane conversion and 

hydrogen selectivity. 

2. Controlling and producing valuable, separable carbon 

allotropes. 

Since solid catalysts have been extensively reviewed, this 

paper will provide a detailed and updated analysis of liquid 

catalysts and discuss the main challenges to commercializing 

methane pyrolysis. It will also review the latest advancements 

in each type of catalyst, outlining their advantages and 

disadvantages see Figure 14. 

 

 
Figure 14.  An overview of the different catalysts used in methane 
pyrolysis [72] 

The autocatalytic pathway for methane pyrolysis is a 
multifaceted, high-temperature process with various routes 
and intermediates [73]. Abanades and colleagues detected 
hydrocarbons, besides methane, along with radicals in the 
outlet stream while investigating methane's thermal 
decomposition [74]. The authors did not specifically pinpoint 
the types of species present. Matheu and collaborators 
constructed a simulated mechanism for methane pyrolysis 
that closely matched existing literature [75]. So, methane 
pyrolysis is seen as a practical and economical way to produce 
hydrogen with minimal emissions at a low cost. 

5. Techno-economic analysis for green hydrogen 

production  

The ever-present threat of climate change propels green 
hydrogen into the spotlight as a potential game-changer in the 
global energy discussion. Experts and analysts around the 
world are highlighting its potential as a game-changer in 
reducing carbon emissions and paving the way for a low-
carbon future. If we're going to unlock the true potential of 
green hydrogen and fight the urgent climate crisis, we need a 
deep understanding of the technologies and economic factors 
surrounding its production right now [76–79]. The future of 
clean energy is getting a significant boost from green 
hydrogen, a fuel produced using renewable sources like 
sunshine and wind [80]. This eco-friendly option is showing 
immense promise across various industries, with significant 
advancements in the technologies that create it. These 
advancements include electrolysis, biomass gasification, and 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

31 

 

even splitting water directly using solar power. One 
fascinating area of exploration is using renewable biomass 
resources like plant matter to generate green hydrogen 
through gasification [80,81]. Additionally, the integration of 
solar water splitting, which directly converts sun energy 
converted to hydrogen [82], displays creative methods that 
are influencing the growth of the green-hydrogen industry. 
Electrolysis advancements, gasification of biomass, and water 
splitting by the sun have accelerated the development of 
green hydrogen production methods Figure 14. Green 
hydrogen (Table 2) is a game-changer due to its versatility 
across various sectors. From powering our industries and 
transportation to generating cleaner electricity, this clean-
burning fuel offers a promising solution for a sustainable 
future (Figure 15). Several techno-economic frameworks 
have been developed to evaluate the viability of green 
hydrogen-generating systems. One of the most popular 
methods is electrolysis, specifically proton exchange 
membrane (PEM) technology, which has evolved 
dramatically. Studies showed PEM electrolysis as an eco-
friendly method of hydrogen production. This approach 
enables the generation of green hydrogen from clean energy 
sources, wind, and solar, whose prices vary from 2.94-3.32 
USD/kgH2 [85,86]. In the research [80] also investigated the 
feasibility of integrating a Ten-megawatt PEM electrolysis 
apparatus with an organic Rankine cycle with waste heat 
recovery to establish economically viable large-scale storage 
of green hydrogen that is sustainable. The study investigates 
the manufacture of hydrogen utilizing solar energy, namely 
photovoltaic systems. It demonstrates the potential for this 
technology to serve as a green hydrogen production method 
in Iraq, playing a part in a global zero-emissions economy. 
This research highlights the potential of biomass gasification 
technology as a game-changer in producing clean, sustainable 
hydrogen. This technology holds particular promise for 
tackling decarbonization challenges in sectors like industrial 
heating and even home heating systems [86].  

 

The study especially looked at whether gasification of 
biomass might be used in the US to produce hydrogen. It 
yielded valuable insights regarding the economic costs, 
environmental impact of biomass sources, and the technical 
hurdles and successes of generating hydrogen through this 
method [87]. The research investigates the generation of 
hydrogen from combustion of biomass and gives a thorough 
analysis of the current challenges and possible prospects, 
particularly in establishing a comprehensive pathway for this 
process. Edou et al. [39] researched the production of a 
significant amount of hydrogen using gasification using a 
fluidized bed , Steam reformation of biogas  from breaking 
down anaerobically (AD) , and various other thermo-chemical 
technologies. Among these, fluidized bed gasification (FB) 
emerged as the most cost-effective method, producing 
hydrogen at $3.40/kg for potential use in public 
transportation buses. AD-biogas reforming followed at 
$4.20/kg. Additionally, Arcos et al. [40] discussed 
photocatalysis, a method that utilizes light to produce 
hydrogen gas [88,89]. The research explores thermo-
chemical water splitting (TWS) as a viable method for large-
scale production of clean hydrogen, emphasizing that 
optimization can reduce costs and environmental impact. It 
introduces ceria thermochemical water-splitting (TCWS) as 
an innovative technique for solar hydrogen synthesis, 
improving hydrogen production with solar-heated nitrogen. 
Another advanced technology, developed by Mehrpooya et al., 
incorporates solar thermal energy, An overheated heat pump, 
a natural cycle of Rankine, and a four-phase thermochemical 
cycle for Cu-Cl, achieving a hydrogen production rate of 21.75 
kg/h. Additionally, the Power-to-Hydrogen-to-Combined 
Heat and Power (PtH2tCHP) system offers a cost-effective, 
low-emission approach that supports a low-carbon, clean 
energy infrastructure. The study also indicates that the 
generation of hydrogen using renewable resources could 
become as cost-effective as conventional techniques in 
countries with strict carbon pricing [91–95]. 

 Figure 15. Indicators of both technological advancements and economic viability across different global technologies for green hydrogen 

production [60,83,84]. 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

32 

 

 

 

 

 

 

 

 

 

 

 

 

 

6. Recent advances and innovations 

  In recent years, significant progress has been made in 
green hydrogen production technologies, improving their 
efficiency, cost-effectiveness, and scalability. The current cost 
of green hydrogen typically falls between $2.50 and $6.80 per 
kilogram [96]. However, the declining costs of renewable 
energy and electrolyzers are driving down the price of green 
hydrogen, making it increasingly competitive with blue 
hydrogen. The decreasing costs of renewable energy and 
electrolysers are effectively lowering the price of green 
hydrogen, making it more competitive with blue hydrogen. 
The United States Department of Energy aims to reduce 
hydrogen production costs to $1 per kilogram by 2030. Table 
3 outlines recent hydrogen production technologies, detailing 
their sources, processes, benefits, drawbacks, and maturity. 
Due to data limitations, life cycle assessments and techno-
economic analyses are not included. Figure 16 summarizes 
these technologies, focusing on ESMR, SOEC, AEM, BPV and 
DAE as key methods. Electrolysis powered by wind or hydro-
generated electricity is considered one of the most effective 
methods for producing green hydrogen [97]. Of the three 
electrolysis methods, solid oxide electrolysis cells (SOECs) are 
regarded as the most efficient for hydrogen production. Table 
3 (Appendix) indicates that SOECs outperform other 
methods, achieving efficiencies of up to 90%, the highest 
among hydrogen production technologies [98]. SOECs use 
ceramic electrolytes instead of hydroxide exchange 
membranes, resulting in lower material costs despite a longer 
initial setup time. They are currently at a technology 
readiness level (TRL) of 6–7, indicating readiness for 
demonstration and commercialization. However, their 
lifespan of less than two to three years contrasts with PEM 
and alkaline electrolysis technologies, which typically last 10-
20 years. The current emphasis of our research and 
development endeavors is on extending the operational 
lifespan of Solid Oxide Electrolysis Cells (SOECs) [99]. AEMs 
represent a new era in high-efficiency energy devices, 
characterized by their strong mechanical, thermal, and 
chemical properties that address fuel crossover and 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  
carbonation challenges seen in traditional alkaline fuel cells 
utilizing aqueous KOH [100]. AEMs are approaching 
readiness for demonstration and commercialization, while 
ESMR holds promise in reducing GHG emissions but faces 
methane leakage and high energy consumption issues. 
Hydroxide exchange membrane water electrolyzers show 
potential for efficient hydrogen production, yet 
improvements are needed in durability and commercial 
viability [101]. A range of emerging green hydrogen 
technologies, such as AEM and PEM electrolysis, SOECs, 
ESMR, DAE, and MECs, are progressing towards applications 
in transportation and industry. These innovations aim to 
mitigate emissions, improve energy efficiency, and support 
the shift towards cleaner energy sources. As these 
technologies advance and achieve greater cost efficiency, they 
will undoubtedly play a pivotal role in catapulting us into a 
sustainable energy future. 

 

Figure 16.  Latest innovations in green hydrogen production [118] 

7. Challenges and solutions 

Clean hydrogen's potential for a global energy shift is 
hampered by two main challenges. First, the infrastructure 
needed to use hydrogen widely is still under development. 
This lack of infrastructure is a major roadblock to widespread 
adoption. Second, producing clean hydrogen using renewable 
energy sources is currently too expensive (Figure 17).  

Table 2. Various studies conducted for the advancement of the green hydrogen production 

Literature perspective on the various studies conducted for the advancement of green hydrogen production 

Year technology Yield of H2 Cost of H2 Production Capital Cost Operational cost Ref. 

2023 proton exchange 
membrane (PEM) 

electrolysis 

– 2.94–3.32 USD/kgH2 600 USD/kW 1.5% of Capex [86] 

2023 photovoltaic energy 
system 

– 3.79–4.11 USD/kgH2 1.29 × 106 USD 7,166.76 USD/yr [90] 

2023 PEM coupled with 
waste heat recovery 

and an ORC 

– – 79.29 × 106 £ 133.92–283.80 £/MW [80] 

2023 biomass gasification 94.9–99.1 kg H2/ 
ton of biomass 

3.47–4.11 USD/kgH2 1.7–2.51 × 108 USD 24.55–29.95 USD/kgH2 [87] 

2023 thermochemical 
water-splitting 

168.3 kg/h 3.92 USD/kg H2 48.3 × 106 USD 15.6 × 106 USD/yr [91] 

2022 integrated systems 
of Power-to- 
Hydrogen-to- 

Combined Heat and 
Power 

– 5.76 V/kg 700-1500 V/kW 3 V/MW [92] 

 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

33 

 

 

 
As a result, most hydrogen production relies on fossil fuels 
like natural gas and coal, which undermines its 
environmental benefits [119]. Despite current regulatory 
hurdles, the clean hydrogen industry is making significant 
progress, with many industries and companies incorporating 
green hydrogen into their products. The growing demand for 
green hydrogen indicates its potential to become a highly 
sought-after renewable energy source shortly. The increasing 
recognition of its significance spurs the advancement of more 
environmentally friendly technologies and global approval. 
The significant recent decrease in the costs of renewable 
energy clearly indicates that producing hydrogen from 
renewable power through the power-to-gas process will 
become more cost-effective [120]. Some methods of making 
hydrogen, like electrolysis, use a lot of water. In fact, it takes 
roughly 9 kilograms of water to produce just 1 kilogram of 
hydrogen [121]. For over 200 years, scientists and engineers 
have been refining water electrolysis techniques for 
industrial use. This development can be broadly categorized 
into five distinct phases. Each phase is characterized by its 
own set of challenges, technological advancements, and 
contributions to the overall progress of water electrolysis 
technology (as illustrated in Figure 18). 

Hydrogen can indeed be used in traditional engines, but 
it unfortunately produces nitrogen oxide emissions and is not 
as efficient as fuel cells. Nevertheless, the environmental 
advantages of hydrogen fuel cannot be disregarded. The 
scarcity of hydrogen stations and fuel cells' exorbitant prices 
are the principal factors contributing to the limited presence 
of H2-powered cars on the roads today. The limited 
availability of hydrogen fueling stations presents an 
opportunity for expanding the market for hydrogen vehicles. 
As more stations are built, it will encourage more people to 
consider purchasing hydrogen vehicles, leading to a positive 
cycle of growth for the industry. It is a chicken-and-egg 
situation [123]. Storing hydrogen in its liquid form is tricky 
because it needs super cold temperatures and special 
equipment.  

 
 
 
That's why scientists are putting a lot of effort into 

developing technology that can convert hydrogen from 
electrolysis (made with renewable energy sources) into 
liquid fuels like diesel, methanol, or ammonia. This would be 
a game-changer! These fuels are easier to transport, allowing 
us to move clean energy from places with lots of renewable 
resources to areas with limited options [124]. Adding to the 
challenges, safety is a major concern with hydrogen. Because 
it's highly flammable and can ignite easily under many 
conditions, there are significant worries about its safe 
handling and use. 

8. Solution to the challenges 

The fight against climate change hinges on researchers 
developing clean ways to produce hydrogen. But for it to be 
truly impactful, industries need solutions for transporting, 
storing, and distributing hydrogen – including making it 
readily available in rural areas. Governments also have a 
critical role. They need to craft policies that make green 
hydrogen a key player in the global shift towards a clean, 
reliable, and affordable energy system. This includes securing 
domestic supplies of zero-carbon hydrogen, as current 
production methods are expensive and limited in scale. The 
current infrastructure simply can't handle large-scale 
storage, long-distance transportation, and distribution of 
liquefied hydrogen [125].  No country is currently self-
sufficient in carbon-neutral or zero-carbon hydrogen, 
meaning imports will be necessary. Hydrogen energy's 
potential for the future relies on global competition and 
consumer demand. For instance, for hydrogen-powered 
vehicles to succeed, they need to be priced competitively 
compared to other options. Right now, the lack of hydrogen 
stations and high refueling costs are major roadblocks for fuel 
cell vehicles. However, with increased demand, economies of 
scale could bring down refueling costs. Hydrogen might find 
its biggest advantage in powering heavy-duty vehicles like 
buses, trains, and industrial trucks used in mining. This is 
because fuel cells excel where high energy storage per weight 
is crucial [126].  

Figure 17. Current challenges and potentials of hydrogen production [118] 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

34 

 

 

Figure 18. Water electrolysis generation wise development [122] 

The utilization of hydrogen in sectors such as methanol 
production and refining is expected to experience gradual 
expansion by the year 2050, a major shift is expected for 
hydrogen as a fuel. The use of hydrogen as an energy source 
is anticipated to increase significantly by the year 2030, 
making up a significant portion (35%) of total hydrogen 
demand by 2050 [127]. Our present energy infrastructure, 
which has evolved over decades, is a complicated network of 
extraction, processing, and transportation. The transition to a 
hydrogen-based system will be sluggish, maybe spanning 
many decades. Rebuilding or changing a huge percentage of 
existing infrastructure is a significant challenge for hydrogen. 
Furthermore, hydrogen will face fierce competition from 
alternative energy sources. The economic effect of the COVID-
19 epidemic may postpone this transformation even further. 
Policymakers must identify cost-effective ways to incorporate 
hydrogen and investigate how the hydrogen and natural gas 
businesses might collaborate, possibly complementing one 
another. 

9. Applications and impact 

Hydrogen is employed in various industries, such as 

electricity generation, transportation, processing, medicine, 

chemical production, heating, and steelmaking [128]. 

Environmentally friendly hydrogen's benefits include its 

compatibility with existing natural gas pipelines for storage 

and transport, which can be readily adapted for hydrogen use. 

Green hydrogen offers the advantage of being stored and 

transported through existing natural gas pipelines, making it 

distinct from other energy storage types. The natural gas 

infrastructure can be easily adapted for hydrogen transport 

Transportation across air, sea, and land can become carbon-

free with hydrogen. Some examples of such cars include 

HFCVs, EVs, and NGVs, which stand for natural gas vehicles 

[129]. Given its advantages compared to alternative energy 

storage technologies, P2H could be an extremely efficient 

option for addressing challenges in transitioning to  

 

 

 

 

renewable energy, offering reliable, cost-effective, efficient, 

long-term, and high-capacity storage [129]. 

10. Production method wise applications 

In water electrolysis, external energy flows through a 

circuit to drive a reaction that splits water molecules into 

hydrogen and oxygen atoms, a process known as dissociation. 

Combining photocatalysis with electrocatalysis, the 

technique behind photoelectrocatalysis (PEC), which work 

together to enhance this electrochemical reaction [130]. At 

the anode, water undergoes oxidation, producing oxygen gas, 

protons, and electrons. These protons pass through the 

proton exchange membrane electrolysis (PEMEL) and are 

then reduced, where they react with electrons to produce 

gaseous hydrogen at the cathode. Future work on Proton 

Exchange Membrane Electrolyzers (PEMEL) includes the 

following: 

Higher temperature operation: Operating at temperatures 

between 60°C and 120°C is critical for enhancing voltage 

efficiency. However, higher temperatures can dehydrate the 

PEM, so maintaining adequate water content is essential 

[131]. 

Increased operating pressure: Another important area of 
research is increasing the operational pressure of PEMEL 
systems. Higher pressure is crucial for the widespread use of 
hydrogen, particularly in hydrogen plants, due to the very low 
volumetric energy density of hydrogen gas under ambient 
conditions. Currently, mechanical compressors are used to 
pressurize hydrogen gas, but they are inefficient and noisy 
(Figure 19). AEL can create significant volumes of clean 
hydrogen. Featuring an 8-year membrane and electrode 
exchange, an operational efficiency of 62-82%, and a lifespan 
of up to 30 years, this equipment is reliable and safe. 
Fundamentally, two terminals are immersed in an aqueous 
solution containing 25-30% KOH or NaOH. KOH is used for its 
higher ionic conductivity and lower CO2 solubility. The 
positive electrode generates oxygen, while the negative 
electrode generates hydrogen [132]. 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

35 

 

 

Figure 19. The basic methods of green hydrogen technology [131] 

11. Photovoltaic (PV) systems with electrolyzers 
a. One cutting-edge method of producing and storing energy 

is a PV system that incorporates an electrolyzer. 
b. This system harnesses solar power to produce electricity, 

which is then used by the electrolyzer to split water into 
hydrogen and oxygen. 

c. A research examines photovoltaic (PV) on-grid systems 
that include electrolyzer technology. The paper presents a 
techno-economic model for PV-linked electrolysis facilities 
that takes into account the dynamics of the system. 

d. Water electrolysis-coupled PV off-grid systems are 
efficient. 

11.1 Solar-powered water-splitting system 
a. Three state-of-the-art PEMELs with a total area of 730 cm² 

and a bifacial (SHJ) solar module make up a dependable 
solar-powered water purification system. 

b. The system parameters, including the cell count, 
inclination, and elevation of the solar panel, were fine-
tuned for optimal performance. 

c. At an irradiation level of 1000 W/m², the system achieves 
an 11.55% efficiency in converting solar energy to 
hydrogen. 

12. Wind turbines with electrolyzers 
a. Wind turbines are a promising renewable energy source, 

but their intermittent nature poses challenges. 
b. Wind turbines generate extra power that electrolyzers may 

store and utilize as fuel. 
c. This technique improves wind energy dependability and 

efficiency, enabling clean energy transition. 
d. Electrolysis wind turbines produce green hydrogen and 

sell excess energy to the grid when hydrogen storage is full. 
e. Factors affecting wind energy production include wind 

speed at the site, tower height, and blade diameter. 
f. Frequent wind power fluctuations can cause electrolyzers 

(AEL) to start up and shut down frequently, reducing 
hydrogen production. 

g. Supercapacitors can be integrated into a wind/hydrogen 
(W/H₂) grid-tied system for attenuating wind power 
variations. 

13. Hybrid Microgrid (HµG) 
a. The proposed hybrid microgrid comprises three 

distributed generation (DG) units: two that are wind-and 
solar-powered, and remaining using Proton Exchange 
Membrane Fuel Cell (PEMFC) technology (Figure 20). 

b. The AEL in the system balances the variable renewable 
energy sources (VRES) by producing hydrogen. 

 
 

 
 
 

c. When there is excess generation, hydrogen is stored in a 
hydrogen tank and used to feed the fuel cell during low 
generation periods. 

d. The hydrogen microgrid demonstrates the benefits of using 
hydrogen to store energy produced by sun and wind 
systems, enhancing system self-sufficiency [133–136]. 

 
14. Policy and Regulatory Framework 

The World Bank Group is actively advancing green 
hydrogen initiatives in Latin America, with countries such as 
Brazil, Costa Rica, Colombia, Panama, and Chile actively 
exploring its potential for fuel and energy storage. This 
renewable energy option is gaining attention on a global scale, 
with Australia, China, India, Japan, Bangladesh, and Germany 
all emphasizing its significance in their energy shifts [137]. 
It's worth noting that Sub-Saharan Africa holds the greatest 
potential for producing green hydrogen (2715 EJ), followed 
by the Middle East and North Africa (2023 EJ), North America 
(1314 EJ), and Oceania (1272 EJ). India's National Hydrogen 
Mission exemplifies this global focus. The recently unveiled 
initial phase of its Green Hydrogen Policy aims to position the 
country as a leader in this domain. Targeting a production 
capacity of 5 million metric tons per annum (MMTPA) by 
2030, the policy also emphasizes boosting renewable energy 
sources and offering incentives to attract investment in green 
hydrogen and ammonia production. This initiative comes 
amid projections of India's hydrogen consumption doubling 
to 6.7 million tonnes per year by 2030 [138]. Currently, most 
hydrogen is utilized by industries like steel mills, fertilizer 
plants, and oil refineries as a process fuel. The challenge? 
While green hydrogen boasts a lower environmental impact, 
it is not yet cost-competitive with its "grey" counterpart 
derived from valuable fossil fuel sources like natural gas or 
naphtha, despite its decreasing costs of renewable electricity 
[139]. Looking towards the future, Japan's Ministry of 
Economy, Trade and Industry (METI) is outlining a roadmap 
for establishing a global hydrogen supply chain by 2030. 
Their Strategic Roadmap and Basic Hydrogen Plan for 
Hydrogen and Fuel Cell highlight the potential of NH3 as a 
low-carbon fuel option. Bangladesh is expanding its energy 
diversification efforts with a hydrogen research facility, 
emphasizing a cost-efficient solar-wind hybrid power plant 
model along its coastline [140]. Germany's forward-looking 
hydrogen policy involves significant state funding for green 
hydrogen initiatives, alongside research into low-carbon 
hydrogen options, positioning the country as a leader in 
technology development and international partnerships to 
ensure energy security [141].  

 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

36 

 

 
Figure 20. Hybrid system for green hydrogen production 

China's 2021–2035 hydrogen energy plan aims to 
establish a robust industry by 2025 and scale up renewable 
hydrogen production, targeting significant carbon emissions 
reductions. By 2035, China plans to rely heavily on renewable 
hydrogen to advance its transition to sustainable energy 
sources [142]. The UK is working to build a hydrogen 
economy with flexible guidelines focused on long-term 
decarbonization and economic benefits, in alignment with 
national goals.  

 

 

 

 

By 2030, it aims to lead in low-carbon hydrogen 
production, supporting both carbon reduction and economic 
growth. The strategy emphasizes adaptability to market 
changes and explores various technologies to meet Carbon 
Budget 6 and net zero targets by 2050 [143]. 

15. Future directions and research gaps 
 Future research should prioritize advancing green 

hydrogen technologies to TRL 5–6. Researchers need to 

improve production methods, industries must develop better 

systems for storage, transportation, and distribution, and 

governments should create policies that support a 

sustainable and secure energy future. Addressing the high 

costs and infrastructure limitations is crucial for making 

green hydrogen a viable energy source [125]. Governments in 

every country depend significantly on importing carbon-

neutral and zero-carbon hydrogen to meet their domestic 

needs. The effectiveness of hydrogen energy systems in the 

future hinges on competitive market conditions and demand. 

Challenges such as insufficient refueling infrastructure and 

expensive hydrogen refueling costs are barriers to the 

widespread use of fuel cell vehicles at present, but increased 

demand could drive down costs as economies of scale come 

into play [126]. While traditional hydrogen applications, like 

making methanol and refining oil, are expected to grow 

slowly by 2050, the future looks bright for its use as a fuel. 

Demand in this sector is predicted to skyrocket after 2030, 

accounting for a significant portion (35%) of total hydrogen 

demand by mid-century [127]. However, transitioning our 

energy infrastructure to accommodate this shift is a complex 

undertaking, potentially spanning decades. The challenge lies 

in adapting existing systems and navigating competition from 

other energy sources. Economic hurdles, like the recent 

COVID-19 pandemic, could further slow down this progress. 

To address these obstacles, policymakers must find cost-

effective transition strategies and encourage collaboration 

between the hydrogen and natural gas sectors (Figure 21). 

 

 

 

 

Figure 21. To ensure the successful development of green hydrogen, it is crucial for the government, hydrogen producers, and researchers to 

work together actively [118] 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

37 

 

16. Conclusion 

Green hydrogen is at the forefront of the global energy 

transition, presenting a versatile and sustainable alternative 

to conventional fossil fuels. This comprehensive review has 

elucidated the multifaceted approaches to green hydrogen 

production, including water electrolysis, biomass gasification, 

and thermochemical processes. Among these, water 

electrolysis stands out due to its maturity and scalability, 

particularly through the use of alkaline and PEM 

electrolyzers. However, the efficiency and cost-effectiveness 

of these technologies remain challenges that require 

continued research and development. Significant 

advancements in electrocatalysts and electrode materials 

have shown promise in enhancing the efficiency of hydrogen 

production. For instance, the development of bifunctional 

electrocatalysts and heterostructured interfaces has led to 

lower overpotentials and increased stability, crucial for both 

hydrogen evolution reactions (HER) and oxygen evolution 

reactions (OER). Additionally, the integration of renewable 

energy sources, such as solar and wind, with hydrogen 

production systems offers a pathway to further reduce 

environmental impacts and improve energy security. The 

importance of green hydrogen extends beyond energy 

production; it is integral to decarbonizing sectors like 

transportation, industry, and power generation. This 

transition is critical as nations worldwide strive to meet their 

climate goals, particularly the ambitious goal of reaching zero 

emissions by the year 2050. The successful implementation of 

green hydrogen technologies can significantly mitigate CO2 

emissions, combat climate change, and foster sustainable 

economic growth. Despite the progress, several research gaps 

and commercial limitations need to be addressed. Key areas 

for future research include improving the efficiency of 

electrolysis processes, developing low-cost and durable 

materials, and enhancing hydrogen storage and distribution 

systems. Policy support and strategic investments are 

essential to accelerate the deployment of green hydrogen 

technologies and realize their full potential in the energy 

transition. 

Ethical issue 
The authors are aware of and comply with best practices in 
publication ethics, specifically concerning authorship 
(avoidance of guest authorship), dual submission, 
manipulation of figures, competing interests, and compliance 
with policies on research ethics. The authors adhere to 
publication requirements that the submitted work is original 
and has not been published elsewhere in any language. 

Data availability statement 
Data sharing does not apply to this article as no datasets were 

generated or analyzed during the current study.  

Conflict of interest 

The authors declare no potential conflict of interest. 

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MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

44 

 

Appendix I 

Table 3. Latest innovations in green hydrogen production [118] 

Process Sources Process and range Advantages Challenges TRL Cost of production Ref. 

Solid oxide 
electrolyser cells 
(SOECs) 

Steam heat 
sources include: 
1. Utilization of 
thermal energy 
waste from 
industry. 
2. Harnessing 
heat energy 
from solar and 
geothermal 
systems. 
3. Generation of 
heat through 
nuclear power. 

1202–1832 ◦ F, <25 bar 1. Able to maintain 
very high rates of 
electrochemical 
reactions, with current 
densities greater than 
1 A/cm². 
2.Demonstrates 
excellent load-
following ability, thus 
well-suited for use with 
intermittent renewable 
energy. 
3.Produces compact 
systems that take up 
less space than those 
using liquid-alkaline 
electrolytes. 
4.Perfect for on-site 
usage. 
5.Less-cost materials, 
utilizing ceramics for 
the electrolyte. 
6.Can function in alter 
mode. 

1. Cellular constituent 
parts deterioration. 
2.The gasket or 
electrolyte fails, 
allowing the gas to 
escape. 
 3. Unstable mechanical 
conditions caused by 
thermal stress. 
 
 4. Extended start-up 
and break-in durations. 

6–7 Capital expenditures 
for solid oxide 
electrolysers are 
estimated to be around 
$2,000/kW based on 
Irena's estimations for 
2020. 

[102,103] 

Methane pyrolysis/ 
splitting 

Source of 
energy: 
Electricity 
Feedstock: 
Methane 

>1472 ◦ F 1.Straight CO2 
emissions are 
absent. 

2.Forms solid carbon, 
resulting in carbon 
black. 

1. Significant heat 
wastages may impair its 
efficiency. 
 2. Needs high-
temperature plasma. 

3–6 Hydrogen 
produced by 
methane 
pyrolysis 
now costs 
between 
$2,600 and 
$3,200 per 
metric ton, 
with the 
exact amount 
dependent on 
the price of 
carbon. 

  

[104] 

Electrified steam 
methane reforming 
(ESMR) 

(Methane) 
extracted from 
natural gas 

1. The 
formative 
years 
 2.Reforming 
3.Shift change 
4.CO2 removal 
5.Compression 
and 
purification 

6.Utilisation 

1.Amenable 
to 
incorporating 
carbon 
capture, 
utilization, 
and maintain 
(CCUS) to 
lower CO2 
emissions. 

2.Can decrease the cost 
of decarbonizing H2 
production. 

1. As of right 
now, the 
procedure 
costs more 
than 
conventional 
SMR. 
 2. The 
possibility of 
methane 
seepage. 

  

3–4 A particular 
investment 
cost of about 
422 
Euros/kW 
net 
equivalent is 
associated 
with 
traditional 
steam 
reforming 
that does not 
use CCS. 

  

[105] 

Anion exchange 
membranes (AEMs) 

Membrane: 
solid polymer 
electrolyte 

Using  catalyst of 
transition metals (CeO2–
La2O) 

1.Doesn’t rely 
on Pt. 

2.Utilizes an 
AEM to serve 
as a solid 
electrolyte, 
thereby 
obstructing 
damage from 
corrosive 
electrolytes. 

3.Operates 
effectively in 
acidic 
settings. 

1. Not as 
robust. 
 2. Not as 
steady. 
 3. Poor 
performance 
in hot and 
high pressure 
environments. 

  

6–7 (for 
lab 
scale 
system) 

Hydrogen 
generation 
costs utilizing 
AEM-based 
water 
electrolysis 
are 
anticipated to 
be $2 to 
$3/kg. The 
use of metals 
from the non-
platinum 
group and 
the 
effectiveness 
of the AEMs 
in facilitating 
hydroxide 
conduction 
and limiting 
fuel 

[106,107] 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

45 

 

4.Demonstrates 
reduced internal 
resistance and high 
levels of conductivity. 

crossover 
both 
contribute to 
the 
competitive 
cost and 
improve the 
electrolyzers' 
overall 
performance 
and 
durability. 

  
Hydroxide exchange 
membrane water 
electrolyzers 

Highly-purified 
water as the 
feedstock 

Make use of an 
electrolyte that is 
hydroxide exchange 
membrane to separate 
oxygen and hydrogen 
from water. 

1.Utilizes catalysts 
devoid of platinum 
group metals. 
2.Enables the use of 
economical stack 
components such as 
stainless steel, 
preserving the 
advantages of 
membrane-based 
technologies. 

1. In order to function, 
electrolytes must be 
supported, rather than 
liquid water. 
 2. The solid-state 
ionomers are immature. 
 3. Not very long-lasting.  
4. Not fully developed 
technology. 
 5. Ionomer breakdown 
occurs quickly. 

3-5 Depending on the 
exact configurations 
and operating 
circumstances used, 
the projected 
production cost of 
hydrogen utilizing 
HEME ranges from 
around $2.50 to $4.50 
per kilogram. Factors 
such as material cost, 
manufacturing size, 
and electrolyser 
efficiency determine 
this price range. 

[108–
110] 

Direct air 
electrolysis (DAE) 

External input: 
Such as solar 
panels, tidal, 
geothermal, or 
wind 
Water source: 
Water 
Oxygen source: 
Atmospheric air 
Electrolyte: 
Alkaline 
solution such as 
KOH 

Directly produce 
hydrogen from 
atmospheric CO2 using 
an electrochemical 
technique 

1.Harnesses renewable 
energy sources. 
2.Scalable in size. 
3.Demonstrates high 
efficiency. 
4.Cost-effective by 
eliminating the need 
for expensive 
membranes or 
electrodes. 

1. The expense of initial 
investment is great. 
 2. A number of 
variables, such as 
catalysts, pressure, and 
temperature, must be 
carefully controlled. 
 3. Hydrogen 
production is low. 

4-6 the cost of hydrogen 
production using DAE 
is estimated to be 
around $2.5 to $3 per 
kilogram of hydrogen. 
This cost is 
comparable to other 
environmentally 
friendly methods for 
producing hydrogen 
that harness 
renewable energy 

[111] 

Biophotovoltaics 
(BPV)/ 
Biophotoelectrolysis 
cell (BPE)/Microbial 
electrolysis cells 
(MEC) 

Employing 
photosynthetic 
microorganisms 
like algae and 
cyanobacteria 

By using biological 
photosynthetic 
materials, solar energy 
may be transformed into 
electrical current. 

1. Converts industrial 
CO2 waste into a feed 
for microorganisms, 
offering a sustainable 
and economical route 
for hydrogen 
production. 
2. The technology is 
environmentally sound 
and generates almost 
less harmful emissions 
or pollutants. 

1.The goal is to use 
microbial electron 
transport pathways to 
transfer electrons to a 
solid-state anode. 
2. The experimental 
setup lacks 
comparability and 
standardisation. 
3. The devices' current 
outputs are quite low. 

1-3 Hydrogen generation 
with BPE devices is 
now estimated to cost 
between $2.5 and 
$3/kg, which is 
competitive with other 
environmentally 
friendly ways of 
hydrogen 
production.Depending 
on the design and 
operating conditions, 
MECs can create 
hydrogen for $2.75 to 
$4.00 per kilogram, 
according to recent 
study. 

[102,112–
114] 

Membrane-less 
electrolysers 

Source: 
Different types 
of high-
conductivity 
aqueous 
electrolytes 

The electrodes that 
evolve H2 and O2 do not 
have a diaphragm or 
membrane divider. 

1. Requires fewer and 
simpler components 
(anode, cathode, and 
device body), leading 
to reduced 
manufacturing and 
assembly costs. 
2. Simplifies device 
complexity. 
3.Shows potential for 
robust devices that can 
withstand severe 
operating conditions 
without membrane 
damage, have high 
impurity tolerance, and 
long operational 
lifetimes. 
4.Capable of 
functioning with a 
variety of aqueous 
conductive 
electrolytes. 

1. The decreased 
voltage efficiency was 
caused by the high 
operational current 
densities (≥0.5 A cm-2) 
that resulted from the 
increased ohmic 
solution (IR) losses. The 
ohmic voltage loss is 
larger in most 
membrane-less 
electrolysers because 
the ion transport 
distance is longer, 
which increases the 
total ohmic resistance 
(Rs) of the electrolytic 
solution. 
2. It is difficult to 
produce and sustain a 
large enough pressure 
gradient between the 
electrodes to conduct 
electrochemical 
hydrogen compression. 

4.3 An estimated $2 to 
$2.5 per kilogram of 
hydrogen may be 
produced utilizing 
electrolysers that do 
not use membranes. 
 

[101,115] 



MFI Chowdhury et al. /Future Energy                                                                                 November 2024| Volume 03 | Issue 04| Pages 18-46 

46 

 

 No, it can't 
manufacture hydrogen 
with a purity level of 
99.99% when 
compared to PEM. 
 Fourthly, difficulties 
associated with 
materials. 
 5. Issues with scaling-
up. 

Redox decoupling Source: Water 
or solutions 
with alkaline 
properties 

1) Use electricity to 
separate water into its 
component hydrogen 
and oxygen. 
 Has a two-step process: 
(i) The OER is the 
process by which 
oxygen is formed; (ii) 
the HER is the process 
by which hydrogen is 
formed. 

1.Utilizes redox-
mediated reactions in 
dual electrochemical 
cycles to produce high-
purity hydrogen from 
alkaline solutions. 
2.Shows consistent and 
rapid hydrogen 
production with nearly 
perfect steady-state 
faradaic efficiency. 

Because of the inherent 
relationship between 
OER and HER, any 
changes or 
improvements to one 
will have an effect on 
the other. 

2-4 One method that might 
bring the price of 
hydrogen generation 
down to about $2/kg is 
an electrochemical and 
thermally-activated 
chemical (ETAC) cycle, 
which has shown an 
efficiency of 98.7 
percent. 

[116,117] 

 

 

 

 

 

 

 

 

 

 

 

 

 


