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Journal Food and Environment Safety of the Suceava University – FOOD ENGINEERING, 
Year IX, No1 - 2010 

 

 64 

STUDIES REGARDING THE EFFICIENCY OF A DIRECT METHANOL FUEL 
CELL (DMFC) 

 
Violeta VASILACHE  

 

Stefan cel Mare University of Suceava, Faculty of Food Engineering. 13 th University Street, 720229, Romania, 
E-mail adress: violetav@usv.ro  

 
 

 
Abstract: Combustion cells are devices which transform chemical energy into electric and thermal 
energy. There could be an acceptable solution to the problem of alternative sources of energy, for a lot 
of practical applications. DMFC combustion cell (DMFC – direct methanol fuel cell) uses methanol, 
instead of hydrogen, so it works safely. More, the storage of combustible does not represent a difficult 
problem, like the hydrogen storage presents. A reforming device is not necessary, because the cell 
itself transforms methanol into hydrogen protons, free electrons and CO2. The absence of reforming 
device make this type of cell more adapted for automotive applications where the objective is to have a 
simple source of electric power. A polymeric membrane which could conduct protons is used as 
electrolyte. The technology DMFC (direct methanol fuel cell) is in fact a variant of PEMFC (polymer 
electrolyte membrane fuel cell) technology, which was developed having hydrogen as combustible. 
Using chemical reactions, the efficiency was calculated theoretically to find the possibilities of 
increasing it. Thermodynamic considerations were also used to complete the efficiency study. Finally, 
using scientific data, a calculus was performed. 

 
Keywords: methanol fuel cell, material and energy balance, thermodynamic  

 
 
 
 

Introduction (actual state of research) 
 

Surampidi and co. have studied the effect 
of temperature and of the methanol 
concentration through efficiency in a 
DMFC. The performances were measured 
at 30ºC, 60ºC and 90°C respectively, and 
the results prove an increase of 
performances with increasing the 
temperature. They worked with 
concentrations of 0,5, 2,0 and 4,0 M;  
higher voltage was obtained for 2,0 M 
concentration when the current density was 
higher too. Optimal concentration was 
between 0,5 and 2,0 M. Jung and co. 
studied the effect of working temperature 
for the range 60-120°C and of the 
methanol concentration for the range 0,5-
4,0 M. The methanol flow on anode was 9 
ml/min and the pure oxygen flow was 105 

sccm. The results also confirmed the fact 
that performances of the cell are increasing 
with temperature and the optimal 
concentration was 2,5 M. Nakagawa and 
Xiu studied a cell in the temperatures range 
from 30ºC to 100°C and the effect of 
proportion of oxidant gas (air and pure 
oxygen respectively)[1,2,3,4]. 
Recent studies at Los Alamos National 
Laboratory (LANL) focalized on possible 
applications of DMFC as principal and 
auxiliary power source for vehicles and as 
a portable power source for the range 1-
100 W. The conditions in exploitation force 
some restrictions, so working temperatures 
have not to be higher than 100°C and the 
consumption of precious metals has to be 
reduced at minimum. For portable power 
sources the temperature should not exceed 
80°C, but the power demands are reduced, 



Journal Food and Environment Safety of the Suceava University – FOOD ENGINEERING, 
Year IX, No1 - 2010 

 

 65 

fact that imposes a decreasing of 
consumption of noble metals [5,6]. 

 
Theory, studies, results and discussion 

 
Function of a DMFC is based on next 
phases: 
Phase1. Those two gases, oxygen (air) and 
methanol, maintained in two separated 
tanks – oxygen on the cathode side and 
methanol on anode side, flow from tank to 
catalyzer. 
Phase2. Methanol (CH3OH) reacts with 
water forming carbon dioxide and 
hydrogen. At catalyzer side, hydrogen is 
decomposed into two atoms of H+ 
(protons) and every atom yields its electron 
in this process[7,8]. 
Phase3. Protons pass through electrolyte 
(polymeric membrane capable to conduct 
protons) and displace to cathode. 
Phase4. Electrons migrate from anode to 
cathode and generate an electric current 
(electric power). 
Phase5. At contact with cathode, four 
electrons always recombine with an 
oxygen molecule. 
Phase6. Just formed oxygen ions have a 
negative electric charge, and furthermore 
react with protons forming water. 
The chemical reactions occurring are: 
At anode side: 

CH3OH + H2O → CO2 + 6H+ + 6e-  
(oxidation)  (1) 

At cathode side: 
3/2O2 + 6H+ + 6e- → 3H2O 

 (reduction)  (2) 
Total reaction: 

CH3OH + 3/2O2 →  CO2 + 2H2O
    (3) 

The efficiency of a combustion cell can be 
measured by measuring the potential curve 
V(I). Generally the next relation should be 
taken into consideration: 

 
V(I)=ε0 – ηact(I) – ηohm(I) – ηconc(I),      (4) 

 
where ε0 is a constant term which 

represents the value of potential difference 
of the cell in open circuit (I=0); ηact(I) is a 
logarithmic term (activation over-
potential), which represents a lose 
connected with the activation energy for 
starting electrochemical reactions, 
important for lower values of the current 
density; ηohm(I) is a linear term, 
representing potential drop due to the ohm 
resistance of the electrolyte, electrodes and 
conductors; ηconc(I) is an exponential term 
(diffusion or concentration over-potential), 
which represents the lose due to reactants 
reactivity variation on interface, important 
for high values of current density. 

 

 
 

Figure.1. Image of a DMFC: water, methanol and 
protons change membrane (PEM) 

 
For a thermal engine the maximum 
theoretic efficiency is that of a Carnot 
cycle: 

ηC=1 – T2/T1,              (5) 
where T1 and T2 are absolute temperatures 
of hot source and cold source respectively; 
for combustion cell, maximum efficiency 
is expressed by the ratio between free 
energy Gibbs (ΔG) and the variation of 
free enthalpy (ΔH) in electrochemical 
reaction: 

ηpc= ΔG/ ΔH .             (6) 
The global conversion efficiency of a 
combustion cell is superior to that of a 



Journal Food and Environment Safety of the Suceava University – FOOD ENGINEERING, 
Year IX, No1 - 2010 

 

 66 

thermal engine. 
 

Thermodynamics of transformations 
chemical energy – electric energy give: 

– ΔG = Lutil,      ΔG = ΔH – TΔS    (7) 

The work-function of the electrical charge 
is giving by relation: 

Lutil = nFΔE          or      –ΔG = nFΔE (8) 
where, n=number of electrons  
participating in reaction, E = e.m.f. (V) 
(electromotive force), F = Faraday’s 
constant. 
The heat produced is given by the relation:  

Q = TΔS = ΔH – ΔG.           (9) 
For a general chemical reaction: 

   
   ba

dc

BA
DC

RTGG ln0   (10) 

which could be written for an ideal gas,  
 
  i

i

reactpart

prodpart
RTGG








..

..
ln0 (11) 

where ΔG0 is Gibbs free energy in standard 
conditions (P=760mmHg, T=25C°C), νi 
are stoichiometric coefficients of reaction. 

Assuming that: – ΔG = nFΔE, on 
obtains: 

 
 


i

i

partprod

partreact
RTEE





.

.
ln0  (12) 

For standard conditions it follows, E = E0. 
In irreversible thermodynamics there are 
loses due to: 1. Ohmic polarization – due 
to resistance phenomena when ions pass 
through electrolyte and electrons pass 
through interface. 2. Concentration 
polarization – due to quickly consumption 
of reactants on electrodes surface and 
appearing of concentration gradients. 3. 
Activation polarization – refers to surpass 
of a initial threshold potential ΔVact similar 
with the case of concentration polarization. 
The efficiency is defined after the relation: 

LHV

elel

E
E

nFLHV
nFL

LHV
L

      (13) 

LHV represents the heat obtained by 
combustion of a mol of combustible (J/mol 
combustible). ELHV represents the electric 
equivalent of caloric inferior power of the 
combustible. 
Then the potential difference of the cell is: 

 
Vc=E – ΔVohm – ΔVconc – ΔVact .   (14) 

 
Here, ΔVohm represents potential drop due 
to electric resistance of the cell, ΔVconc 
potential drop due to concentration 
variation and ΔVact potential drop due to 
initial activation processes. Subsequent 
sources of losing are bonded by the way of 
using combustible and air. 

inH

consH
comb m

m
U

,

,

2

2              or        (15) 

inOHCH

consOHCH
comb m

m
U

,

,

3

3   .               (16) 

Here Ucomb is the ratio which describes the 
efficiency of combustible utilization, and 
m are masses of combustibles consumed, 
and initial masses respectively. It follows 
that:  

LHV

combc

E
UV

   .                 (17) 

If one particularizes electrochemical 
oxidation of methanol, it follows assuming 
that a=1, b=3/2, c=1 and d=2, 

   
    232

1
3

2
2

1
20 ln

OOHCH
OHCO

RTGG    

(18) 
fact which diminishes ΔG comparing with 
ΔG0, and consequently a decreasing of 
efficiency. As a general rule, valid for 
combustion cells, the removal of formed 
water should be ensured, because it 
induces a decrease of methanol solution 
concentration. In this case, of direct 
methanol fuel cell, it works with totally 
immersed electrodes, which simplify the 
problem from the mechanical point of 
view. Ideal condition consists of complete 
penetration of electrolyte into porosity of 



Journal Food and Environment Safety of the Suceava University – FOOD ENGINEERING, 
Year IX, No1 - 2010 

 

 67 

the electrode. It is pointed to obtain a 
higher percent of volume porosity, pores-
free. The dimension of particles have to be 
chosen to obtain a good contact through 
them and with support layer, in order to 
facilitate electronic conductibility in all 
electrode volume [9,10,11]. 
The reaction rate in the pores of the 
electrode, in every point, is dependent by 
interface potential, current density which 
flows through interface electrode-
electrolyte; by the concentration of 
reactant species which arrive in pores, and 
by nature of electro-catalyzer deposited on 
electrode. These local conditions are 
depended by mass transfer of reactant 
species and by current transport to a 
specified point and by this point to another 
interface. So, to make a complete 
characterization of the porous electrode it 
is necessary to know the distribution of 
reaction in all electrode volume. 

A calculus example is presented here: 
Global reaction:  
 
 CH3OH + 3/2 O2 → CO2 + 2H2O 
 
For ideal conditions: 

Kmol/Kg32M OH3CH = ;

Kmol/Kg32M
2O

=  
On anode:  
CH3OH + H2O → CO2 + 6H+ + 6e- 
So, every CH3OH molecule produces 

6e-. 
1Kmol CH3OH : 

6eNQ A ••= ;   
Q = 5,78208 . 108C 
Total produced energy is (U=1,21V) 
W = Q.U = 6,99....108J       Or,  
W = 194,3 kWh 
For real conditions:  
 U = 0,82 V (from literature) 
5% lost by intermediate reactions, so 

the efficiency, %95oltanme   

C10...492,595,06eNQ 8A =•••=  

kWh125J105,4

82,010...492,5UQW
8

8

=•=

==•=
 

%64
kWh3,194

kWh125
W
W

ideal

real
energetic ===η  

 
References 

 
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engineering of the direct methanol fuel cell, J. 
Power Sources 86 (2000), pp. 469–477 
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Performance of a direct methanol polymer 
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