Electrophoretic deposition of YSZ layers on pyrolytic graphite and a porous anode substrate based on NiO-YSZ published by Ural Federal University eISSN2411-1414; chimicatechnoacta.ru LETTER 2022, vol. 9(4), No. 20229425 DOI: 10.15826/chimtech.2022.9.4.25 1 of 6 Electrophoretic deposition of YSZ layers on pyrolytic graphite and a porous anode substrate based on NiO–YSZ Artem V. Solovev a* , George N. Starostin ab , Inna A. Zvonareva ab , Stanislav S. Tulenin a , Vyacheslav F. Markov ac a: Ural Federal University named after the First President of Russia B. N. Yeltsin, Ekaterinburg 620002, Russia b: Institute of High Temperature Electrochemistry, Ekaterinburg 620660, Russia c: Ural Institute of the State Fire Service of the Ministry of Emergency Situations of Russia, Ekaterinburg 620062, Russia * Corresponding author: tom1799@yandex.ru This paper belongs to a Regular Issue. © 2022, the Authors. This article is published in open access under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). 1. Introduction Currently, there is an increased interest in the development of novel electrical energy storage and production facilities, in particular, power plants based on solid oxide fuel cells (SOFC) [1, 2]. The advantages of such devices are the absence of harmful emissions and thermal pollution, higher efficiency, scalability, noiselessness in operation, and low energy consumption [3–5]. However, the mass production and use of solid oxide fuel cells are constrained by their high operating temperatures (1073–1273 К), at which the conductivity of the main component of the SOFC – the oxygen–ion electrolyte – reaches a sufficient level. At high temperatures, degradation processes and chemical inter- actions among components in the membrane-electrode block of fuel cells are accelerated [6]. All this imposes strict requirements on the materials used, causes a high cost of SOFCs, and significantly limits their further production [7]. Application of a thin-film electrolyte based on zirconium dioxide stabilized with 3 to 10 mol.% of yttrium oxide is an effective solution to the problem of reducing the operating temperature of the SOFC since decreasing the thickness of the electrolyte leads to a decrease in the internal resistance of the element and an increase in its power [8, 9]. One of the most rapidly expanding fields in electrochemistry right now is the development of fuel cells using a thin-film solid oxide electrolyte [10, 11]. The electrophoretic deposition (EPD) of a solid electrolyte on the surface of the anode or cathode appears to be the most appealing among the potential techniques for producing such films because it is cost-effective and does not require complicated hardware design [12–14]. The cost of obtaining ceramic layers of YSZ will be significantly reduced by using precursors from Abstract Solid oxide fuel cells are promising hydrogen energy devices. The goal of this research was to create ceramic layers for SOFCs based on yttria- stabilized zirconia (YSZ) and to investigate their parameters. YSZ ceramic layers with a thickness of 5.14 μm on a porous NiO–YSZ substrate and 7 μm on pyrolytic graphite were obtained by electrophoretic deposition. X-ray diffraction and electron microscopy were used to determine the composition, structure, and morphological features of ceramic layers. The effects of the substrate's nature, the degree of dispersion of the initial YSZ powder, and the heat treatment conditions on the properties of the ceramic layer YSZ were considered. Keywords zirconium dioxide yttrium oxide hydrogen energy solid oxide fuel cell electrophoretic deposition YSZ Received: 05.11.22 Revised: 01.12.22 Accepted: 02.12.22 Available online: 09.12.22 Key findings ● Ceramic layers based on zirconium dioxide stabilized with yttrium oxide were obtained by electrophoretic deposition. ● The thickness of the obtained ceramic layers was 5.14 μm on a porous NiO–YSZ anode substrate and 7 μm on pyrolytic graphite. ● The dependence of the EPD process efficiency on the precursor dispersion degree was established. http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2022.9.4.25 mailto:tom1799@yandex.ru http://creativecommons.org/licenses/by/4.0/ https://orcid.org/0000-0003-0269-1119 https://orcid.org/0000-0001-9836-0896 https://orcid.org/0000-0002-9793-1375 https://orcid.org/0000-0003-3941-4748 https://orcid.org/0000-0003-0758-2958 https://crossmark.crossref.org/dialog/?doi=https://doi.org/10.15826/chimtech.2022.9.4.25&domain=pdf&date_stamp=2022-12-09 Chimica Techno Acta 2022, vol. 9(4), No. 20229425 LETTER 2 of 6 domestic production, such as high-quality powder of the DCI-1 brand with an affordable price and large volumes of industrial production. The EPD method allows controlling the morphology and output parameters of the resulting ceramic coatings and obtaining layers with good adhesive properties and with a higher density compared to coatings obtained by other methods [15, 16]. The purpose of this research was to obtain ceramic layers of YSZ and analyze their morphology and crystal structure. Electrophoretic deposition was carried out on pyrolytic graphite and a porous NiO–YSZ anode substrate. 2. Experimental The EPD process includes three main stages. The first stage is the preparation of a stable suspension of the applied oxide material in a suitable liquid dispersion medium. The second one is the application of an electric field to the suspension, causing the movement of the particles to the electrode and their deposition on it. The last one is the drying and sintering of the resulting coating. 2.1. Preparation of the suspension A 1:1 mixture of acetylacetone СН₃СОСН₂СОСН₃ (p.a.) and isopropanol CH₃CH(OH)CH₃ (puriss) was used as the starting reagent for the preparation of a stable suspension. As a polymer binder that prevents cracking, a BMA-5 (butyl methacrylate-methacrylic acid copolymer, SRI Polymers, Russia) copolymer was added to the prepared mixture, which was dissolved in the mixture for 48 h. Commercial zirconium dioxide powder stabilized with yttrium oxide (Zr0.97Y0.03O2–δ) grade DCI-1, (JSC ChMP, Russia), with an average particle size of 75 μm, was milled in a planetary mill, FRITSCH PULVERISETTE 7, for 4 h at 500 rpm. Grinding with zirconium dioxide balls was carried out in an acetone environment. During the grinding process, 4 samples of YSZ powder were taken at an interval of 1 h. Figure S1 shows the X-ray diffraction pattern of the commercial powder DCI-1. Then, a portion of the milled powder in the amount of 65 g·l–1 was added to the prepared dispersion medium and dispersed on a submersible ultrasonic disperser UZDN-A at an emitter frequency of 22 kHz for 15 min. 2.2. Used substrate material Pyrolytic graphite and porous anode substrates based on NiO–YSZ with a nickel foil sublayer were used as substrate materials for electrophoretic deposition. A nickel substrate in the form of a foil with a thickness of 100 μm provided the conductive paths, since NiO–YSZ is a non-conductive substrate [17] (Figure 1a). Pyrolytic graphite substrates were obtained by chemical vapor deposition (CVD). The thickness of the substrates was 1 mm. The ohmic resistance of the material was 2±0.4 Ω. Graphite substrates were used to study the influence of the nature of the substrate material on the morphology of the ceramic coating. The multilayer joint rolling of films method was used to create porous anodic NiO–YSZ substrates (mass ratio of precursors NiO:YSZ:starch = 60:40:20). The thickness of NiO–YSZ was 0.87 mm. 2.3. Electrophoretic deposition of YSZ Electrophoretic deposition was carried out at 298 K with a voltage of 60 V applied between the electrodes in two cycles of 10 minutes. The cathode and anode were fixed in a specially designed holder at a distance of 10 mm from each other and immersed in a reactor with a prepared suspension (Figure 1b). Pyrolytic graphite was used as a counter electrode. The resulting coatings underwent heat treatments at 973 K, 1173 K, and 1573 K for 2 h. X-ray phase analysis was performed on a Rigaku D/MAX-2200VL diffractometer. The survey was conducted in Cu Kα radiation at 10° ≤ 2θ ≤ 90°. On a JEOL JSM-5900 LV microscope, morphological characteristics of the obtained YSZ layers were examined using scanning electron microscopy (SEM). The MEASURER software was used to process the obtained SEM data in order to establish the average particle size. Figure 1 Electric field distribution scheme on the NiO–YSZ surface (a), where 1 – nickel foil, 2 – porous anode substrate based on NiO– YSZ, 3 – electric field lines, 4 – charged ceramic YSZ particles. Schematic diagram of an installation for electrophoretic deposition (b), where 1 – reactor, 2 – counter electrode, 3 – porous anode substrate based on NiO–YSZ, 4 – suspension, 5 – electric current source. Chimica Techno Acta 2022, vol. 9(4), No. 20229425 LETTER 3 of 6 3. Results and Discussion One of the main aspects of obtaining a high-quality coating in the EPD process is the presence of a stable dispersion of YSZ. The formation of a dense, well-anchored coating is possible only if the EPD proceeds in sedimentationally and aggregatively stable suspensions [18–20]. The stability of the suspension is influenced by the choice of the dispersion medium and the ratio of the initial components. According to [21–24], it is preferable to carry out electrophoretic deposition in non-aqueous organic media, as alcohols, ketones, and their mixtures are most often used. When conducting EPD in aqueous media, electrochemical reactions occur that are accompanied by the release of gasses that significantly affect the process [25]. For this reason, an anhydrous dispersion medium consisting of acetylacetone and isopropanol has proven itself in the best way. This is due to the fact that isopropanol is less hygroscopic than ethanol, which ensures the stability of the physicochemical characteristics of the suspension. Acetylacetone contains the carbonyl group, which is capable of donor-acceptor interaction with the surface of the oxides [26]. Indeed, the stability of such suspensions, according to light transmission data at wavelengths of 540, 800, and 1000 nm, was at least 50 h. The spectral methods, in particular, spectrophotometry, quite accurately indicate the beginning of the sedimentation process in the suspension volume, which is caused by the aggregation and coagulation of particles over time. The gradual removal of small particles from the suspension leads to an increase in transmission at the beginning at small wavelengths, with the gradual settling of large particles at large wavelengths. Figure 2a shows a plot of the stability of the suspension over time. An important condition for successful EPD is the size of the YSZ particles in the suspension and the absence of aggregation of these particles in the dispersion medium. It is worth noting that with a size of less than 1 μm, particles can remain in suspension for a long time due to Brownian motion [27]. Also, for a positive result in conducting EPD, it is necessary that the YSZ powder has a narrow particle size distribution. To achieve this, grinding in planetary mills and ultrasonic dispersion are used. According to the results, an increase in the powder grinding time leads to a decrease in the average particle size from 4 μm to 0.9 μm with a single-modal distribution (Figure 2b). The percentage of particles with a size of from 2.5 to 7.5 μm after 1 h of grinding was 84%, but after 4 h of grinding, 90% of particles were from 0.5 to 2 μm (Figure 2c). After dispersing the ground ceramic particles from their suspensions by the EPD method, YSZ-based layers with a thickness of up to 7 μm on pyrolytic graphite were successfully obtained. However, the high-quality coatings without cracks and with a small particle size distribution were obtained from suspensions containing powder ground in a planetary mill for 4 h on NiO–YSZ substrates up to 5.14 μm thick. The X-ray phase analysis showed that the formed ceramic coating consists of two phases: zirconium dioxide stabilized with yttrium oxide in an amount of 3 mol.% (95.68%) and zirconium dioxide in an amount of 4.32%, which is apparently due to the presence of residual ZrO2 in the initial commercial powder DCI-1. Figure 3 shows the X-ray diffraction pattern of the YSZ sample deposited on a porous NiO-YSZ anode substrate. According to the XRD data, zirconium dioxide, stabilized by 3 mol.% yttrium oxide, has a tetragonal structure with crystal lattice parameters a = 3.6249(3) Å, c = 5.1275(1) Å with a predominant growth direction (101). The phase of individual zirconium dioxide has a cubic lattice with a parameter a = 5.1522(1) Å and a predominant growth direction (111). Figure 2 Dependence of the light transmission of the suspension on time, at wavelength (a), nm: 540 (1), 800 (2), 1000 (3). Average YSZ particle sizes with grinding time (b), in h: 1, 2, 3, 4. A histogram of the distribution of YSZ particles by size. The grinding time of the precursor was 4 h (c). Chimica Techno Acta 2022, vol. 9(4), No. 20229425 LETTER 4 of 6 Pyrolytic graphite and a porous anode substrate NiO– YSZ with a nickel foil sublayer were used as the substrates for the deposition of YSZ in order to study the impact of the substrate material on the coating structure. It was possible to create a uniform coating made of zirconium dioxide with a thickness of up to 7 μm thanks to the higher conductivity of graphite substrates. After drying for 24 h at room temperature, the ceramic layer was fixed and free of visible cracks. However, following heat treatment at temperatures between 973 and 1173 K, the YSZ layer peeled off the substrate material and microcracks as large as 3 μm in width appeared. This phenomenon can be attributed to significant variations in the thermal expansion coefficients of graphite and YSZ [28]. In addition, thin layers of graphite deform at high temperatures, and the graphite substrate collapses, which leads to direct deformation and cracking of the deposited layer of zirconium dioxide stabilized with yttrium oxide on this substrate material. Deposition of YSZ on porous anode substrates based on NiO–YSZ gave different results. The high porosity of the material allowed YSZ particles to penetrate into the near- surface layer during electrophoretic deposition and fix themselves on the substrate. The surface of the ceramic YSZ layer that was deposited on a non-conductive NiO–YSZ coating is depicted in the SEM image in Figure 4a. Since in the course of thermal studies it was found that the temperature of 1173 K is not sufficient for sintering the deposited layer consisting mainly of irregularly shaped particles, due to the higher melting point of the NiO–YSZ anode substrate [29], the YSZ functional layers were annealed at a temperature of 1573 K for 2 h. Figures 4b and 4c show SEM images of the surface of the ceramic layer and the end part of the YSZ layer on the NiO–YSZ substrate after heat treatment. The resulting layer had a thickness of 5.14 μm. The YSZ particles can be seen to have started to sinter with one another, losing the distinct grain boundaries, and there is also no evidence of the particle aggregation that was seen during the deposition on graphite. 4. Conclusions In this work, YSZ suspensions based on an isopropanol, acetylacetone, and BMA-5 copolymer mixture were successfully produced. It was discovered that as the initial YSZ powder was ground for longer periods of time, the suspensions became more stable as the average particle size decreased from 4 to 0.9 μm and the quality of the ceramic coatings that were deposited improved. The prepared suspension's stability time exceeded 50 h. By using the EPD method, ceramic layers on NiO–YSZ and pyrolytic graphite substrates were successfully produced. The obtained YSZ layers have the crystal lattice parameters a = 3.6249(3) Å, c = 5.1275(1) Å and are composed of tetragonal zirconium dioxide stabilized by 3 mol.% yttrium oxide. Figure 3 X-ray diffraction pattern of the YSZ layer deposited on a porous NiO–YSZ anode substrate. Figure 4 SEM images of the obtained YSZ layer on a Ni–YSZ substrate before (a) and after heat treatment at 1573 K (b). SEM image of the end of the YSZ layer; the heat treatment temperature was 1573 K (c). Chimica Techno Acta 2022, vol. 9(4), No. 20229425 LETTER 5 of 6 It was determined that the EPD of YSZ undergoes successfully on a porous NiO–YSZ anode substrate with a nickel foil sublayer, ensuring that the deposited layers of YSZ are up to 5.14 μm thick. The thickness of the YSZ layers obtained on graphite was 7 μm. The EPD method can be used to apply ceramic layers on non-conductive substrates by using a nickel plate as a sublayer of NiO–YSZ. The use of EPD and inexpensive commercial powders greatly simplifies and reduces the cost of the process of obtaining ceramic coatings, which allows better integration into the green energy agenda. Supplementary materials This manuscript contains supplementary materials, which are available on a corresponding online page. Funding The research funding from the Ministry of Science and Higher Education of the Russian Federation (Ural Federal University project within the Priority-2030 Program) is gratefully acknowledged. Acknowledgments None. Author contributions Conceptualization: V.F.M. Data curation: A.V.S., S.S.T. Formal Analysis: A.V.S., S.S.T. Funding acquisition: A.V.S. Investigation: G.N.S., I.A.Z. Methodology: A.V.S., S.S.T. Project administration: V.F.M. Resources: A.V.S. Software: A.V.S., G.N.S., I.A.Z. Supervision: S.S.T., V.F.M. Validation: S.S.T. Visualization: A.V.S. Writing – original draft: A.V.S. Writing – review & editing: S.S.T., V.F.M. Conflict of interest The authors declare no conflict of interest. Additional information Author IDs: George N. Starostin, Scopus ID 57882347600; Inna A. Zvonareva, Scopus ID 57209229327; Stanislav S. Tulenin, Scopus ID 55189942200; Vyacheslav F. Markov, Scopus ID 7201577312. Websites: Ural Federal University, https://urfu.ru/ru; Institute of High Temperature Electrochemistry, http://www.ihte.uran.ru Ural Institute of the State Fire Service of the Ministry of Emergency Situations of Russia, https://uigps.ru/ob-institute. References 1. Proskuryakova L. Foresight for the ‘energy’priority of the Russian Science and Technology Strategy. Energy Strateg Rev. 2019;26:100378. doi:10.1016/j.esr.2019.100378 2. Yang B, Li Y, Li J, Shu H, Zhao X, Ren Y. Comprehensive summary of solid oxide fuel cell control: a state-of-the-art review. Protect Control Modern Power Systems. 2022;7(1):1– 31. doi:10.1186/s41601-022-00251-0 3. Giorgi L, Leccese F. Fuel cells: Technologies and applications. Open Fuel Cells J. 2013;6(1):1–20. doi:10.2174/1875932720130719001 4. Connor P. Solid oxide fuels cells: facts and figures. Springer. 2013;163–180. doi:10.1007/978-1-4471-4456-4_1 5. Choudhury A, Chandra H, Arora A. Application of solid oxide fuel cell technology for power generation – A review. Renewable Sustainable Energy Rev. 2013;20:430–442. doi:10.1016/j.rser.2012.11.031 6. Savignat SB., Chiron M., Barthet C. Tape casting of new electrolyte and anode materials for SOFCs operated at intermediate temperature. J Eur Ceram Soc. 2007;27(2– 3):673–678. doi:10.1016/j.jeurceramsoc.2006.04.049 7. Dunyshkina LA. Vvedenie v metody polucheniya plenochnykh elektrolitov dlya tverdooksidnykh toplivnykh elementov: monografiya. Ekaterinburg: UrO RAS; 2015. 125 p. Russian. 8. Gao Z, Mogni LV, Miller EC, Railsback JG, Barnett SA. A perspective on low-temperature solid oxide fuel cells. Energy Environment Sci. 2016;9(5):1602–1644. doi:10.1039/C5EE03858H 9. Cooper SJ, Brandon NP. Solid oxide fuel cell lifetime and reliability: critical challenges in fuel cells. London: Academic Press. 2017; 223 p. 10. Ramadhani F, Hussain MA, Mokhlis H, Hajimolana S. Optimization strategies for Solid Oxide Fuel Cell (SOFC) application: A literature survey. Renewable Sustainable Energy Rev. 2017;76:460–484. doi:10.1016/j.rser.2017.03.052 11. Singh B, Ghosh S, Aich S, Roy B. Low temperature solid oxide electrolytes (LT-SOE): A review. J Power Sources. 2019;339:103–135. doi:10.1016/j.jpowsour.2016.11.019 12. Kalinina EG, Pikalova EY. New trends in the development of electrophoretic deposition method in the solid oxide fuel cell technology: theoretical approaches, experimental solutions and development prospects. Russ Chem Rev. 2019;88(12):1179. doi:10.1070/RCR4889 13. Pikalova EY, Kalinina EG. Place of electrophoretic deposition among thin-film methods adapted to the solid oxide fuel cell technology: A short review. Int J Energy Prod Manag. 2019;4(1):1–27. doi:10.2495/EQ-V4-N1-1-27 14. Kalinina EY, Pikalova EG. Opportunities, challenges and prospects for electrodeposition of thin-film functional layers in solid oxide fuel cell technology. Mater. 2021;14(19):5584. doi:10.3390/ma14195584 15. Kalinina EG, Pikalova EY, Kolchugin AA, Pikalov SM, Kaigorodov AS. Cyclic electrophoretic deposition of electrolyte thin-films on the porous cathode substrate utilizing stable suspensions of nanopowders. Solid State Ionics. 2017;302:126–132. doi:10.1016/j.ssi.2017.01.016 16. Das D, Basu RN. Suspension chemistry and electrophoretic deposition of zirconia electrolyte on conducting and non- conducting substrates. Mater Res Bull. 2013;48(9):3254– 3261. doi:10.1016/j.materresbull.2013.05.034 https://www.scopus.com/authid/detail.uri?authorId=57882347600 https://www.scopus.com/authid/detail.uri?authorId=57209229327 https://www.scopus.com/authid/detail.uri?authorId=55189942200 https://www.scopus.com/authid/detail.uri?authorId=7201577312 https://urfu.ru/ru http://www.ihte.uran.ru/?page_id=3106 https://doi.org/10.1016/j.esr.2019.100378 https://doi.org/10.1186/s41601-022-00251-0 https://doi.org/10.2174/1875932720130719001 https://doi.org/10.1007/978-1-4471-4456-4_1 https://doi.org/10.1016/j.rser.2012.11.031 https://doi.org/10.1016/j.jeurceramsoc.2006.04.049 https://doi.org/10.1039/C5EE03858H https://doi.org/10.1016/j.rser.2017.03.052 https://doi.org/10.1016/j.jpowsour.2016.11.019 https://doi.org/10.1070/RCR4889 https://doi.org/10.2495/EQ-V4-N1-1-27 https://doi.org/10.3390/ma14195584 https://doi.org/10.1016/j.ssi.2017.01.016 https://doi.org/10.1016/j.materresbull.2013.05.034 Chimica Techno Acta 2022, vol. 9(4), No. 20229425 LETTER 6 of 6 17. Besra L, Compson C, Liu M. Electrophoretic deposition on non-conducting substrates: the case of YSZ film on NiO–YSZ composite substrates for solid oxide fuel cell application. J Power Sources. 2007;173(1):130–136. doi:10.1016/j.jpowsour.2007.04.061 18. Besra L, Liu M. A review on fundamentals and applications of electrophoretic deposition (EPD). Prog Mater Sci. 2007;52(1):1–61. doi:10.1016/j.pmatsci.2006.07.001 19. Corni I, Ryan MP, Boccaccini AR. Electrophoretic deposition: From traditional ceramics to nanotechnology. Journal of the Eur Ceram Soc. 2008;28(7):1353–1367. doi:10.1016/j.jeurceramsoc.2007.12.011 20. Kalinina EG, Pikalova EY, Safronov AP. A study of the electrophoretic deposition of thin-film coatings based on barium cerate nanopowder produced by laser evaporation. Russ J Appl Chem. 2017;90(5):701–707. doi:10.1134/S1070427217050056 21. Pikalova EY, Kalinina EG. Electrophoretic deposition in the solid oxide fuel cell technology: Fundamentals and recent advances. Renewable Sustain Energy Rev. 2019;116:109440. doi:10.1016/j.rser.2019.109440 22. Negishi H, Yamaji K, Sakai N, Horita T, Yanagishita H. Electrophoretic deposition of YSZ powders for solid oxide fuel cells. J Mater Sci. 2004;39(3):833–838. doi:10.1023/B:JMSC.0000012911.86185.13 23. Kalinina EG, Samatov OM, Safronov AP. Stable suspensions of doped ceria nanopowders for electrophoretic deposition of coatings for solid oxide fuel cells. Inorg Mater. 2016;52(8):858–864. doi:10.1134/S0020168516080094 24. Das D, Basu RN. Organic acids as electrostatic dispersing agents to prepare high quality particulate thin film. J Alloys Compd. 2017;729:71–83. doi:10.1016/j.jallcom.2017.09.097 25. Ferrari B, Moreno R. Zirconia thick films deposited on nickel by aqueous electrophoretic deposition. J Electrochem Soc. 2000;147(8):2987. doi:10.1149/1.1393636 26. Fukada YN, Nagarajan W, Mekky W. Electrophoretic deposition—mechanisms, myths and materials. J Mater Sci. 2004;39(3):787–801. doi:10.1023/B:JMSC.0000012906.70457.df 27. Sánchez-Miranda MJ, Sarmiento-Gómez E, Arauz-Lara JL. Brownian motion of optically anisotropic spherical particles in polymeric suspensions. Eur Phys J E. 2015;38(1):1–6. doi:10.1140/epje/i2015-15003-x 28. Kostikova VI, Eremeeva ZhV. Technology of composite materials. Vologda: Infra-Engineering; 2021. 484 p. Russian. 29. Das D, Bagchi B, Basu RN. Nanostructured zirconia thin film fabricated by electrophoretic deposition technique. J Alloys Compd. 2017;693:220–1230. doi:10.1016/j.jallcom.2016.10.088 https://doi.org/10.1016/j.jpowsour.2007.04.061 https://doi.org/10.1016/j.pmatsci.2006.07.001 https://doi.org/10.1016/j.jeurceramsoc.2007.12.011 https://doi.org/10.1134/S1070427217050056 https://doi.org/10.1016/j.rser.2019.109440 https://doi.org/10.1023/B:JMSC.0000012911.86185.13 https://doi.org/10.1134/S0020168516080094 https://doi.org/10.1016/j.jallcom.2017.09.097 https://doi.org/10.1149/1.1393636 https://link.springer.com/article/10.1023/B:JMSC.0000012906.70457.df#auth-N_-Nagarajan https://link.springer.com/article/10.1023/B:JMSC.0000012906.70457.df#auth-W_-Mekky https://doi.org/10.1023/B:JMSC.0000012906.70457.df https://doi.org/10.1140/epje/i2015-15003-x https://doi.org/10.1016/j.jallcom.2016.10.088