Recent breakthroughs in cathode of protonic ceramic fuel cells: Materials, functionalization, and future perspectives

Abstract

Hydrogen stands as a promising energy carrier that plays a pivotal role in addressing global sustainability and achieving carbon neutrality. The conversion of hydrogen energy through fuel cells has emerged as a central technology in this pursuit. Notably, protonic ceramic fuel cells (PCFCs) hold potential for the future hydrogen energy ecosystem, owing to their impressive energy conversion efficiencies at low-to-intermediate temperatures (300–750°C). It is becoming increasingly evident that the development of PCFC technology relies on advancements in the cathode, as oxygen-involved reactions often exhibit sluggish kinetics. In this comprehensive review, we aim to provide an overview of the current state of knowledge concerning the design of advanced cathodes for PCFCs. This includes discussing key descriptors for cathodes, methods for characterizing material properties, and functionalization techniques to enhance electrode performance. Finally, we present insights into future research directions.

Keywords

cathode / electrode functionalization / protonic ceramic fuel cell / triple-conducting oxides

References

[1] Wang Y, Liu T, Lei L, Chen F. High temperature solid oxide H₂O/CO₂ co-electrolysis for syngas production. Fuel Process Technol. 2017; 161: 248-258.

[2] Liu S, Jiang Y, Wang M, et al. Awakening (220) as one more active facet of PtMo alloy via single-atom doping to boost ammonia electrooxidation in direct ammonia fuel cell. Adv Funct Mater. 2023; 33(47): 2306204.

[3] Huan Y, Jiang Y, Wang M, et al. Enhanced alkaline ammonia oxidation reaction activity using PtW alloy catalysts with tungsten as built-in competitor reservoir. Chem Eng J. 2023; 475: 146027.

[4] Tang C, Yao Y, Wang N, et al. Green hydrogen production by intermediate-temperature protonic solid oxide electrolysis cells: advances, challenges, and perspectives. InfoMat. 2024; 6(3): e12515.

[5] Tsvetkov N, Kim D, Jeong I, et al. Advances in materials and interface understanding in protonic ceramic fuel cells. Adv Mater Technol. 2023; 8(20): 2201075.

[6] Duan C, Tong J, Shang M, et al. Readily processed protonic ceramic fuel cells with high performance at low temperatures. Science. 2015; 349(6254): 1321-1326.

[7] Lee JG, Park JH, Shul YG. Tailoring gadolinium-doped ceria-based solid oxide fuel cells to achieve 2 W cm⁻² at 550°C. Nat Commun. 2014; 5(1): 4045.

[8] Song Y, Liu J, Wang Y, et al. Nanocomposites: a new opportunity for developing highly active and durable bifunctional air electrodes for reversible protonic ceramic cells. Adv Energy Mater. 2021; 11(36): 2101899.

[9] Yamazaki Y, Hernandez-Sanchez R, Haile SM. High total proton conductivity in large-grained yttrium-doped barium zirconate. Chem Mater. 2009; 21(13): 2755-2762.

[10] Medvedev DA, Lyagaeva JG, Gorbova EV, Demin AK, Tsiakaras P. Advanced materials for SOFC application: strategies for the development of highly conductive and stable solid oxide proton electrolytes. Prog Mater Sci. 2016; 75: 38-79.

[11] Song Y, Chen Y, Wang W, et al. Self-assembled triple-conducting nanocomposite as a superior protonic ceramic fuel cell cathode. Joule. 2019; 3(11): 2842-2853.

[12] Yang L, Liu Z, Wang S, Choi Y, Zuo C, Liu M. A mixed proton, oxygen ion, and electron conducting cathode for SOFCs based on oxide proton conductors. J Power Sources. 2010; 195(2): 471-474.

[13] Hu B, Aphale AN, Reisert M, et al. Solid oxide electrolysis for hydrogen production: from oxygen ion to proton conducting cells. ECS Trans. 2018; 85(10): 13-20.

[14] Lei L, Tao Z, Wang X, Lemmon JP, Chen F. Intermediate-temperature solid oxide electrolysis cells with thin proton-conducting electrolyte and a robust air electrode. J Mater Chem A Mater. 2017; 5(44): 22945-22951.

[15] Peng R, Wu T, Liu W, Liu X, Meng G. Cathode processes and materials for solid oxide fuel cells with proton conductors as electrolytes. J Mater Chem. 2010; 20(30): 6218-6225.

[16] Ren R, Wang Z, Xu C, et al. Tuning the defects of the triple conducting oxide BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3−δ perovskite toward enhanced cathode activity of protonic ceramic fuel cells. J Mater Chem A Mater. 2019; 7(31): 18365-18372.

[17] Steele BCH. Material science and engineering: the enabling technology for the commercialisation of fuel cell systems. J Mater Sci. 2001; 36(5): 1053-1068.

[18] Adler SB. Factors governing oxygen reduction in solid oxide fuel cell cathodes. Chem Rev. 2004; 104(10): 4791-4844.

[19] Bastidas DM, Tao S, Irvine JTS. A symmetrical solid oxide fuel cell demonstrating redox stable perovskite electrodes. J Mater Chem. 2006; 16(17): 1603-1605.

[20] Wachsman ED, Lee KT. Lowering the temperature of solid oxide fuel cells. Science (1979). 2011; 334(6058): 935-939.

[21] Kreuer KD. Proton conductivity: materials and applications. Chem Mater. 1996; 8(3): 610-641.

[22] Shim JH. Ceramics breakthrough. Nat Energy. 2018; 3(3): 168-169.

[23] Wang N, Tang C, Du L, et al. Advanced cathode materials for protonic ceramic fuel cells: recent progress and future perspectives. Adv Energy Mater. 2022; 12(34): 2201882.

[24] Graves C, Ebbesen SD, Jensen SH, Simonsen SB, Mogensen MB. Eliminating degradation in solid oxide electrochemical cells by reversible operation. Nat Mater. 2015; 14(2): 239-244.

[25] Zheng Y, Wang J, Yu B, et al. A review of high temperature co-electrolysis of H₂O and CO₂ to produce sustainable fuels using solid oxide electrolysis cells (SOECs): advanced materials and technology. Chem Soc Rev. 2017; 46(5): 1427-1463.

[26] Murray EP, Tsai T, Barnett SA. Oxygen transfer processes in (La, Sr) MnO₃/Y₂O₃-stabilized ZrO₂ cathodes: an impedance spectroscopy study. Solid State Ionics. 1998; 110(3-4): 235-243.

[27] Mizusaki J, Yonemura Y, Kamata H, et al. Electronic conductivity, Seebeck coefficient, defect and electronic structure of nonstoichiometric La_1−xSr_xMnO₃. Solid State Ionics. 2000; 132(3-4): 167-180.

[28] Jiang SP. Issues on development of (La, Sr) MnO₃ cathode for solid oxide fuel cells. J Power Sources. 2003; 124(2): 390-402.

[29] Morel B, Roberge R, Savoie S, Napporn TW, Meunier M. Catalytic activity and performance of LSM cathode materials in single chamber SOFC. Appl Catal A Gen. 2007; 323: 181-187.

[30] De Souza R, Harrington G. Revisiting point defects in ionic solids and semiconductors. Nat Mater. 2023; 22(7): 794-797.

[31] Hwang HJ, Moon JW, Lee S, Lee EA. Electrochemical performance of LSCF-based composite cathodes for intermediate temperature SOFCs. J Power Sources. 2005; 145(2): 243-248.

[32] Tietz F, Haanappel VAC, Mai A, Mertens J, Stöver D. Performance of LSCF cathodes in cell tests. J Power Sources. 2006; 156(1): 20-22.

[33] Leng Y, Chan SH, Liu Q. Development of LSCF-GDC composite cathodes for low-temperature solid oxide fuel cells with thin film GDC electrolyte. Int J Hydrog Energy. 2008; 33(14): 3808-3817.

[34] Choi S, Kucharczyk CJ, Liang Y, et al. Exceptional power density and stability at intermediate temperatures in protonic ceramic fuel cells. Nat Energy. 2018; 3(3): 202-210.

[35] Zohourian R, Merkle R, Raimondi G, Maier J. Mixed-conducting perovskites as cathode materials for protonic ceramic fuel cells: understanding the trends in proton uptake. Adv Funct Mater. 2018; 28(35): 1801241.

[36] Poetzsch D, Merkle R, Maier J. Proton uptake in the H+-SOFC cathode material Ba_0.5Sr_0.5Fe_0.8Zn_0.2O_3−δ: transition from hydration to hydrogenation with increasing oxygen partial pressure. Faraday Discuss. 2015; 182: 129-143.

[37] Ni M, Shao Z. Fuel cells that operate at 300 to 500°C. Science (1979). 2020; 369(6500): 138-139.

[38] Kreuer KD. Aspects of the formation and mobility of protonic charge carriers and the stability of perovskite-type oxides. Solid State Ionics. 1999; 125(1-4): 285-302.

[39] Zohourian R, Merkle R, Maier J. Bulk defect chemistry of PCFC cathode materials: discussion of defect interactions. ECS Trans. 2017; 77(10): 133-138.

[40] Kim JH, Jang K, Lim DK, et al. Self-assembled nano-composite perovskites as highly efficient and robust hybrid cathodes for solid oxide fuel cells. J Mater Chem A. 2022; 10(5): 2496-2508.

[41] Poetzsch D, Merkle R, Maier J. Oxygen reduction at dense thin-film microelectrodes on a proton-conducting electrolyte: I. Considerations on reaction mechanism and electronic leakage effects. J Electrochem Soc. 2015; 162(9): F939-F950.

[42] Papac M, Stevanović V, Zakutayev A, O'Hayre R. Triple ionic-electronic conducting oxides for next-generation electrochemical devices. Nat Mater. 2021; 20(3): 301-313.

[43] Suntivich J, Gasteiger HA, Yabuuchi N, Nakanishi H, Goodenough JB, Shao-Horn Y. Design principles for oxygen-reduction activity on perovskite oxide catalysts for fuel cells and metal-air batteries. Nat Chem. 2011; 3(7): 546-550.

[44] Cherry M, Islam MS, Catlow CRA. Oxygen ion migration in perovskite-type oxides. J Solid State Chem. 1995; 118(1): 125-132.

[45] Chroneos A, Yildiz B, Tarancón A, Parfitt D, Kilner JA. Oxygen diffusion in solid oxide fuel cell cathode and electrolyte materials: mechanistic insights from atomistic simulations. Energy Environ Sci. 2011; 4(8): 2774-2789.

[46] De Souza RA. Limits to the rate of oxygen transport in mixed-conducting oxides. J Mater Chem A. 2017; 5(38): 20334-20350.

[47] Hwang J, Rao RR, Giordano L, Katayama Y, Yu Y, Shao-Horn Y. Perovskites in catalysis and electrocatalysis. Science. 2017; 358(6364): 751-756.

[48] Tai LW, Nasrallah MM, Anderson HU, Sparlin DM, Sehlin SR. Structure and electrical properties of La_1−xSr_xCo_1−yFe_yO₃. Part 1. The system La_0.8Sr_0.2Co_1−yFe_yO₃. Solid State Ionics. 1995; 76(3-4): 259-271.

[49] Raffaelle R, Anderson HU, Sparlin DM, Parris PE. Evidence for a crossover from multiple trapping to percolation in the high-temperature electrical conductivity of Mn-doped LaCrO₃. Phys Rev Lett. 1990; 65(11): 1383-1386.

[50] Liu X, Zhao H, Yang J, et al. Lattice characteristics, structure stability and oxygen permeability of BaFe_1−xY_xO_3−δ ceramic membranes. J Membr Sci. 2011; 383(1-2): 235-240.

[51] Kirkpatrick S. Percolation and conduction. Rev Mod Phys. 1973; 45(4): 574-588.

[52] Kim D, Miyoshi S, Tsuchiya T, Yamaguchi S. Percolation conductivity in BaZrO₃-BaFeO₃ solid solutions. Solid State Ionics. 2014; 262: 875-878.

[53] Grimaud A, May KJ, Carlton CE, et al. Double perovskites as a family of highly active catalysts for oxygen evolution in alkaline solution. Nat Commun. 2013; 4(1): 2439.

[54] Lee YL, Kleis J, Rossmeisl J, Shao-Horn Y, Morgan D. Prediction of solid oxide fuel cell cathode activity with first-principles descriptors. Energy Environ Sci. 2011; 4(10): 3966-3970.

[55] Chen Y, Choi Y, Yoo S, et al. A highly efficient multi-phase catalyst dramatically enhances the rate of oxygen reduction. Joule. 2018; 2(5): 938-949.

[56] Hayashi H, Inaba H, Matsuyama M, Lan NG, Dokiya M, Tagawa H. Structural consideration on the ionic conductivity of perovskite-type oxides. Solid State Ionics. 1999; 122(1-4): 1-15.

[57] Kilner JA, Brook RJ. A study of oxygen ion conductivity in doped non-stoichiometric oxides. Solid State Ionics. 1982; 6(3): 237-252.

[58] Kim JH, Kim D, Ahn S, et al. An universal oxygen electrode for reversible solid oxide electrochemical cells at reduced temperatures. Energy Environ Sci. 2023; 16(9): 3803-3814.

[59] Parfitt D, Chroneos A, Tarancón A, Kilner JA. Oxygen ion diffusion in cation ordered/disordered GdBaCo₂O_5+δ. J Mater Chem. 2011; 21(7): 2183-2186.

[60] Choi S, Yoo S, Kim J, et al. Highly efficient and robust cathode materials for low-temperature solid oxide fuel cells: PrBa_0.5Sr_0.5Co_2−xFe_xO_5+δ. Sci Rep. 2013; 3(1): 2426.

[61] Ding H, Wu W, Jiang C, et al. Self-sustainable protonic ceramic electrochemical cells using a triple conducting electrode for hydrogen and power production. Nat Commun. 2020; 11(1): 1907.

[62] Bian W, Wu W, Wang B, et al. Revitalizing interface in protonic ceramic cells by acid etch. Nature. 2022; 604(7906): 479-485.

[63] Chambers MS, McCombie KS, Auckett JE, et al. Hexagonal perovskite related oxide ion conductor Ba₃NbMoO_8.5: phase transition, temperature evolution of the local structure and properties. J Mater Chem A. 2019; 7(44): 25503-25510.

[64] Fop S, McCombie KS, Wildman EJ, et al. High oxide ion and proton conductivity in a disordered hexagonal perovskite. Nat Mater. 2020; 19(7): 752-757.

[65] Yashima M, Tsujiguchi T, Sakuda Y, et al. High oxide-ion conductivity through the interstitial oxygen site in Ba₇Nb₄MoO₂₀-based hexagonal perovskite related oxides. Nat Commun. 2021; 12(1): 556.

[66] Poetzsch D, Merkle R, Maier J. Stoichiometry variation in materials with three mobile carriers—thermodynamics and transport kinetics exemplified for protons, oxygen vacancies, and holes. Adv Funct Mater. 2015; 25(10): 1542-1557.

[67] Poetzsch D, Merkle R, Maier J. Proton conductivity in mixed-conducting BSFZ perovskite from thermogravimetric relaxation. Phys Chem Chem Phys. 2014; 16(31): 16446-16453.

[68] Yu JH, Lee J, Maier J. Peculiar nonmonotonic water incorporation in oxides detected by local in situ optical absorption spectroscopy. Angew Chem Int Ed Engl. 2007; 46(47): 8992-8994.

[69] Duan C, Kee R, Zhu H, et al. Highly efficient reversible protonic ceramic electrochemical cells for power generation and fuel production. Nat Energy. 2019; 4(3): 230-240.

[70] Gao J, Meng Y, Lee S, Tong J, Brinkman KS. Effect of infiltration of barium carbonate nanoparticles on the electrochemical performance of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ cathodes for protonic ceramic fuel cells. JOM. 2019; 71(1): 90-95.

[71] Bae K, Jang DY, Choi HJ, et al. Demonstrating the potential of yttrium-doped barium zirconate electrolyte for high-performance fuel cells. Nat Commun. 2017; 8(1): 14553.

[72] Miao L, Hou J, Gong Z, Jin Z, Liu W. A high-performance cobalt-free Ruddlesden-Popper phase cathode La_1.2Sr_0.8Ni_0.6Fe_0.4O_4+δ for low temperature proton-conducting solid oxide fuel cells. Int J Hydrog Energy. 2019; 44(14): 7531-7537.

[73] Gu CY, Wu XS, Cao JF, et al. High performance Ca-containing La_2−xCa_xNiO_4+δ (0 ≤ x ≤ 0.75) cathode for proton-conducting solid oxide fuel cells. Int J Hydrog Energy. 2020; 45(43): 23422-23432.

[74] Wang Z, Wang Y, Wang J, et al. Rational design of perovskite ferrites as high-performance proton-conducting fuel cell cathodes. Nat Catal. 2022; 5(9): 777-787.

[75] Kim J, Sengodan S, Kwon G, et al. Triple-conducting layered perovskites as cathode materials for proton-conducting solid oxide fuel cells. ChemSusChem. 2014; 7(10): 2811-2815.

[76] Zhou C, Sunarso J, Song Y, et al. New reduced-temperature ceramic fuel cells with dual-ion conducting electrolyte and triple-conducting double perovskite cathode. J Mater Chem A Mater. 2019; 7(21): 13265-13274.

[77] Xia Y, Jin Z, Wang H, et al. A novel cobalt-free cathode with triple-conduction for proton-conducting solid oxide fuel cells with unprecedented performance. J Mater Chem A Mater. 2019; 7(27): 16136-16148.

[78] Zhang X, Jiang Y, Hu X, Sun L, Ling Y. High performance proton-conducting solid oxide fuel cells with a layered perovskite GdBaCuCoO_5+x cathode. Electron Mater Lett. 2018; 14(2): 147-153.

[79] Wang Q, Hou J, Fan Y, et al. Pr₂BaNiMnO_7−δ double-layered Ruddlesden-Popper perovskite oxides as efficient cathode electrocatalysts for low temperature proton conducting solid oxide fuel cells. J Mater Chem A. 2020; 8(16): 7704-7712.

[80] Zhang H, Xu K, He F, et al. Surface regulating of a double-perovskite electrode for protonic ceramic fuel cells to enhance oxygen reduction activity and contaminants poisoning tolerance. Adv Energy Mater. 2022; 12(26): 2200761.

[81] Xu K, Zhang H, Xu Y, et al. An efficient steam-induced Heterostructured air electrode for protonic ceramic electrochemical cells. Adv Funct Mater. 2022; 32(23): 2110998.

[82] Bian W, Wu W, Gao Y, et al. Regulation of cathode mass and charge transfer by structural 3D engineering for protonic ceramic fuel cell at 400°C. Adv Funct Mater. 2021; 31(33): 2s102907.

[83] Ding P, Li W, Zhao H, et al. Review on Ruddlesden-Popper perovskites as cathode for solid oxide fuel cells. J Phys Mater. 2021; 4(2): 22002.

[84] Inprasit T, Limthongkul P, Wongkasemjit S. Sol-gel and solid-state synthesis and property study of La_2−xSr_xNiO₄ (x ≤ 0.8). J Electrochem Soc. 2010; 157(11): B1726.

[85] Gilev AR, Kiselev EA, Cherepanov VA. Oxygen transport phenomena in (La, Sr)₂(Ni, Fe)O₄ materials. J Mater Chem A. 2018; 6(13): 5304-5312.

[86] Saqib M, Choi IG, Bae H, et al. Transition from perovskite to misfit-layered structure materials: a highly oxygen deficient and stable oxygen electrode catalyst. Energy Environ Sci. 2021; 14(4): 2472-2484.

[87] Park K, Bae H, Kim H, et al. Understanding the highly electrocatalytic active mixed triple conducting Na_xCa_3-xCo₄O_9-δ oxygen electrode materials. Adv Energy Mater. 2023; 13(2): 2202999.

[88] Wang N, Hinokuma S, Ina T, Zhu C, Habazaki H, Aoki Y. Mixed proton-electron-oxide ion triple conducting manganite as an efficient cobalt-free cathode for protonic ceramic fuel cells. J Mater Chem A. 2020; 8(21): 11043-11055.

[89] Wang Z, Lv P, Yang L, et al. Ba_0.95La_0.05Fe_0.8Zn_0.2O_3−δ cobalt-free perovskite as a triple-conducting cathode for proton-conducting solid oxide fuel cells. Ceram Int. 2020; 46(11): 18216-18223.

[90] De Blasio C, De Blasio C. Thermogravimetric analysis (TGA). Fundamentals of Biofuels Engineering and Technology; Springer. 2019: 91-102.

[91] Seong A, Jeong D, Kim M, Choi S, Kim G. Performance comparison of composite cathode: mixed ionic and electronic conductor and triple ionic and electronic conductor with BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3−δ for highly efficient protonic ceramic fuel cells. J Power Sources. 2022; 530: 231241.

[92] Acuna W, Tellez JF, Macias MA, Roussel P, Ricote S, Gauthier GH. Synthesis and characterization of BaGa₂O₄ and Ba₃Co₂O₆(CO₃)_0.6 compounds in the search of alternative materials for proton ceramic fuel cell (PCFC). Solid State Sci. 2017; 71: 61-68.

[93] Kim JH, Yoo S, Murphy R, et al. Promotion of oxygen reduction reaction on a double perovskite electrode by a water-induced surface modification. Energy Environ Sci. 2021; 14(3): 1506-1516.

[94] Liang M, He F, Zhou C, et al. Nickel-doped BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3−δ as a new high-performance cathode for both oxygen-ion and proton conducting fuel cells. Chem Eng J. 2021; 420: 127717.

[95] He F, Liang M, Wang W, et al. High-performance proton-conducting fuel cell with b-site-deficient perovskites for all cell components. Energy Fuel. 2020; 34(9): 11464-11471.

[96] Wang X, Li W, Zhou C, et al. Enhanced proton conduction with low oxygen vacancy concentration and favorable hydration for protonic ceramic fuel cells cathode. ACS Appl Mater Interfaces. 2022; 15(1): 1339-1347.

[97] Zhou C, Sunarso J, Dai J, et al. Realizing stable high hydrogen permeation flux through BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3−δ membrane using a thin Pd film protection strategy. J Membr Sci. 2020; 596: 117709.

[98] Seong A, Kim J, Jeong D, et al. Electrokinetic proton transport in triple (H⁺/O²⁻/e⁻) conducting oxides as a key descriptor for highly efficient protonic ceramic fuel cells. Adv Sci. 2021; 8(11): 2004099.

[99] Slodczyk A, Colomban P, Willemin S, Lacroix O, Sala B. Indirect Raman identification of the proton insertion in the high-temperature [Ba/Sr][Zr/Ti]O₃-modified perovskite protonic conductors. J Raman Spectrosc. 2009; 40(5): 513-521.

[100] Colomban P, Zaafrani O, Slodczyk A. Proton content and nature in perovskite ceramic membranes for medium temperature fuel cells and electrolysers. Membranes (Basel). 2012; 2(3): 493-509.

[101] Kim JH, Chern ZY, Yoo S, Deglee B, Wang J, Liu M. Unraveling the mechanism of water-mediated sulfur tolerance via operando surface-enhanced Raman spectroscopy. ACS Appl Mater Interfaces. 2019; 12(2): 2370-2379.

[102] Tang W, Ding H, Bian W, et al. An unbalanced battle in excellence: revealing effect of Ni/Co occupancy on water splitting and oxygen reduction reactions in triple-conducting oxides for protonic ceramic electrochemical cells. Small. 2022; 18(30): 2201953.

[103] Han B, Stoerzinger KA, Tileli V, Gamalski AD, Stach EA, Shao-Horn Y. Nanoscale structural oscillations in perovskite oxides induced by oxygen evolution. Nat Mater. 2017; 16(1): 121-126.

[104] Neagu D, Tsekouras G, Miller DN, Ménard H, Irvine JTS. In situ growth of nanoparticles through control of non-stoichiometry. Nat Chem. 2013; 5(11): 916-923.

[105] Oh D, Colombo F, Nodari L, et al. Rocking chair-like movement of ex-solved nanoparticles on the Ni-Co doped La_0.6Ca_0.4FeO_3−δ oxygen carrier during chemical looping reforming coupled with CO₂ splitting. Appl Catal B. 2023; 332: 122745.

[106] Neagu D, Oh TS, Miller DN, et al. Nano-socketed nickel particles with enhanced coking resistance grown in situ by redox exsolution. Nat Commun. 2015; 6(1): 8120.

[107] Tsekouras G, Neagu D, Irvine JTS. Step-change in high temperature steam electrolysis performance of perovskite oxide cathodes with exsolution of B-site dopants. Energy Environ Sci. 2013; 6(1): 256-266.

[108] Kim KJ, Han H, Defferriere T, et al. Facet-dependent in situ growth of nanoparticles in epitaxial thin films: the role of interfacial energy. J Am Chem Soc. 2019; 141(18): 7509-7517.

[109] Kim JH, Kim JK, Liu J, et al. Nanoparticle ex-solution for supported catalysts: materials design, mechanism and future perspectives. ACS Nano. 2020; 15(1): 81-110.

[110] Kousi K, Tang C, Metcalfe IS, Neagu D. Emergence and future of exsolved materials. Small. 2021; 17(21): 2006479.

[111] Kwon O, Joo S, Choi S, Sengodan S, Kim G. Review on exsolution and its driving forces in perovskites. J Phys Energy. 2020; 2(3): 32001.

[112] Jeong H, Kim YH, Won BR, Jeon H, Park CH, Ha MJ. Emerging exsolution materials for diverse energy applications: design, mechanism, and future prospects. Chem Mater. 2023; 35(10): 3745-3764.

[113] Liang M, Zhu Y, Song Y, et al. A new durable surface nanoparticles-modified perovskite cathode for protonic ceramic fuel cells from selective cation exsolution under oxidizing atmosphere. Adv Mater. 2022; 34(10): 2106379.

[114] Kim JH, Hong J, Lim DK, et al. Water as a hole-predatory instrument to create metal nanoparticles on triple-conducting oxides. Energy Environ Sci. 2022; 15(3): 1097-1105.

[115] Park K, Saqib M, Lee H, et al. Water-mediated exsolution of nanoparticles in alkali metal-doped perovskite structured triple-conducting oxygen electrocatalysts for reversible cells. Energy Environ Sci. 2024; 17(3): 1175-1188.

[116] Ding D, Li X, Lai SY, Gerdes K, Liu M. Enhancing SOFC cathode performance by surface modification through infiltration. Energy Environ Sci. 2014; 7(2): 552-575.

[117] Menezes PW, Indra A, González-Flores D, et al. High-performance oxygen redox catalysis with multifunctional cobalt oxide nanochains: morphology-dependent activity. ACS Catal. 2015; 5(4): 2017-2027.

[118] Kumar K, Canaff C, Rousseau J, et al. Effect of the oxide-carbon heterointerface on the activity of Co₃O₄/NRGO nanocomposites toward ORR and OER. J Phys Chem C. 2016; 120(15): 7949-7958.

[119] Liu F, Sang Y, Ma H, Li Z, Gao Z. Nickel oxide as an effective catalyst for catalytic combustion of methane. J Nat Gas Sci Eng. 2017; 41: 1-6.

[120] Lee H, Jung H, Kim C, et al. Enhanced electrochemical performance and durability of the BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3−δ composite cathode of protonic ceramic fuel cells via forming nickel oxide nanoparticles. ACS Appl Energy Mater. 2021; 4(10): 11564-11573.

[121] Lu X, Yang Z, Zhang J, et al. A cobalt-free Pr₆O₁₁-BaCe_0.2Fe_0.8O_3−δ composite cathode for protonic ceramic fuel cells with promising oxygen reduction activity and hydration ability. J Power Sources. 2024; 599: 234233.

[122] Saqib M, Lee JI, Shin JS, et al. Modification of oxygen-ionic transport barrier of BaCo_0.4Zr_0.1Fe_0.4Y_0.1O₃ steam (air) electrode by impregnating samarium-doped ceria nanoparticles for proton-conducting reversible solid oxide cells. J Electrochem Soc. 2019; 166(12): F746-F754.

[123] Liu B, Jia L, Chi B, Pu J, Li J. A novel PrBaCo₂O_5+σ-BaZr_0.1Ce_0.7Y_0.1Yb_0.1O₃ composite cathode for proton-conducting solid oxide fuel cells. Compos Part B Eng. 2020; 191: 107936.

[124] Cargnello M, Doan-Nguyen VVT, Gordon TR, et al. Control of metal nanocrystal size reveals metal-support interface role for ceria catalysts. Science. 2013; 341(6147): 771-773.

[125] Lee S, Ha H, Bae KT, et al. A measure of active interfaces in supported catalysts for high-temperature reactions. Chem. 2022; 8(3): 815-835.

[126] Subbaraman R, Tripkovic D, Strmcnik D, et al. Enhancing hydrogen evolution activity in water splitting by tailoring Li⁺-Ni(OH)₂-Pt interfaces. Science. 2011; 334(6060): 1256-1260.

[127] Joo S, Seong A, Kwon O, et al. Highly active dry methane reforming catalysts with boosted in situ grown Ni-Fe nanoparticles on perovskite via atomic layer deposition. Sci Adv. 2020; 6(35): eabb1573.

[128] Zhang Y, Chen B, Guan D, et al. Thermal-expansion offset for high-performance fuel cell cathodes. Nature. 2021; 591(7849): 246-251.

[129] Shin JF, Xu W, Zanella M, et al. Self-assembled dynamic perovskite composite cathodes for intermediate temperature solid oxide fuel cells. Nat Energy. 2017; 2(3): 1-7.

[130] Demont A, Sayers R, Tsiamtsouri MA, et al. Single sublattice endotaxial phase separation driven by charge frustration in a complex oxide. J Am Chem Soc. 2013; 135(27): 10114-10123.

[131] Qi H, Zhao Z, Wang X, Tu B, Cheng M. Self-assembled cubic-hexagonal perovskite nanocomposite as intermediate-temperature solid oxide fuel cell cathode. Ceram Int. 2020; 46(14): 22282-22289.

[132] Qi H, Zhang T, Liu D, Cheng M, Tu B. Investigation of a self-assembled Sr_0.74La_0.26CoO_3−δ-SrZr_0.79Co_0.21O_3−δ composite with hierarchical structure as intermediate-temperature solid oxide fuel cell cathode. J Power Sources. 2021; 506: 230230.

[133] Liu F, Deng H, Diercks D, et al. Lowering the operating temperature of protonic ceramic electrochemical cells to <450°C. Nat Energy. 2023; 8(10): 1145-1157.

[134] Chen Y, Yoo S, Choi Y, et al. A highly active, CO₂-tolerant electrode for the oxygen reduction reaction. Energy Environ Sci. 2018; 11(9): 2458-2466.

[135] Zhang Y, Chen Y, Chen F. In-situ quantification of solid oxide fuel cell electrode microstructure by electrochemical impedance spectroscopy. J Power Sources. 2015; 277: 277-285.

[136] Kim JD, Kim GD, Moon JW, et al. Characterization of LSM-YSZ composite electrode by AC impedance spectroscopy. Solid State Ionics. 2001; 143(3-4): 379-389.

[137] Hayd J, Ivers-Tiffée E. Detailed electrochemical study on nanoscaled La_0.6Sr_0.4CoO_3−δ SOFC thin-film cathodes in dry, humid and CO₂-containing atmospheres. J Electrochem Soc. 2013; 160(11): F1197-F1206.

[138] Leonide A, Sonn V, Weber A, Ivers-Tiffée E. Evaluation and modeling of the cell resistance in anode-supported solid oxide fuel cells. J Electrochem Soc. 2007; 155(1): B36.

[139] Chen Y, Bu Y, Zhang Y, et al. A highly efficient and robust nanofiber cathode for solid oxide fuel cells. Adv Energy Mater. 2016; 7(6): 1601890.

[140] Choi Y, Cho HJ, Kim J, et al. Nanofiber composites as highly active and robust anodes for direct-hydrocarbon solid oxide fuel cells. ACS Nano. 2022; 16(9): 14517-14526.

[141] Wu W, Ding H, Zhang Y, et al. 3D self-architectured steam electrode enabled efficient and durable hydrogen production in a proton-conducting solid oxide electrolysis cell at temperatures lower than 600 C. Adv Sci. 2018; 5(11): 1800360.

[142] Goldschmidt VM. Die gesetze der krystallochemie. Naturwissenschaften. 1926; 14(21): 477-485.

[143] Bartel CJ, Sutton C, Goldsmith BR, et al. New tolerance factor to predict the stability of perovskite oxides and halides. Sci Adv. 2019; 5(2): eaav0693.

[144] Kronmüller H. Handbook of Magnetism and Advanced Magnetic Materials; John Wiley & Sons. 2007.

[145] Cook RL, Sammells AF. On the systematic selection of perovskite solid electrolytes for intermediate temperature fuel cells. Solid State Ionics. 1991; 45(3-4): 311-321.

[146] Li Z, Yang M, Park JS, Wei SH, Berry JJ, Zhu K. Stabilizing perovskite structures by tuning tolerance factor: formation of formamidinium and cesium lead iodide solid-state alloys. Chem Mater. 2016; 28(1): 284-292.

[147] Balachandran J, Lin L, Anchell JS, Bridges CA, Ganesh P. Defect genome of cubic perovskites for fuel cell applications. J Phys Chem C. 2017; 121(48): 26637-26647.

[148] Jacobson AJ, Hutchison JL. An investigation of the structure of 12HBaCoO_2.6 by electron microscopy and powder neutron diffraction. J Solid State Chem. 1980; 35(3): 334-340.

[149] Koo B, Kim K, Kim JK, Kwon H, Han JW, Jung W. Sr segregation in perovskite oxides: why it happens and how it exists. Joule. 2018; 2(8): 1476-1499.

[150] Nielsen J, Hagen A, Liu YL. Effect of cathode gas humidification on performance and durability of solid oxide fuel cells. Solid State Ionics. 2010; 181(11-12): 517-524.

[151] Lee W, Han JW, Chen Y, Cai Z, Yildiz B. Cation size mismatch and charge interactions drive dopant segregation at the surfaces of manganite perovskites. J Am Chem Soc. 2013; 135(21): 7909-7925.

[152] Cai Z, Kubicek M, Fleig J, Yildiz B. Chemical Heterogeneities on La_0.6Sr_0.4CoO_3−δ thin films correlations to cathode surface activity and stability. Chem Mater. 2012; 24(6): 1116-1127.

[153] Sharma V, Mahapatra MK, Krishnan S, et al. Effects of moisture on (La, A) MnO₃ (a = Ca, Sr, and Ba) solid oxide fuel cell cathodes: a first-principles and experimental study. J Mater Chem A. 2016; 4(15): 5605-5615.

[154] Niania M, Podor R, Britton TB, et al. In situ study of strontium segregation in La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ in ambient atmospheres using high-temperature environmental scanning electron microscopy. J Mater Chem A. 2018; 6(29): 14120-14135.

[155] An H, Lee HW, Kim BK, et al. A 5 × 5 cm² protonic ceramic fuel cell with a power density of 1.3 W cm⁻² at 600°C. Nat Energy. 2018; 3(10): 870-875.

[156] Seo HG, Staerz A, Kim DS, et al. Reactivation of chromia poisoned oxygen exchange kinetics in mixed conducting solid oxide fuel cell electrodes by serial infiltration of lithia. Energy Environ Sci. 2022; 15(10): 4038-4047.

[157] Kurokawa H, Jacobson CP, DeJonghe LC, Visco SJ. Chromium vaporization of bare and of coated iron-chromium alloys at 1073 K. Solid State Ionics. 2007; 178(3-4): 287-296.

[158] Sachitanand R, Sattari M, Svensson JE, Froitzheim J. Evaluation of the oxidation and Cr evaporation properties of selected FeCr alloys used as SOFC interconnects. Int J Hydrog Energy. 2013; 38(35): 15328-15334.

[159] Le LQ, Hernandez CH, Rodriguez MH, et al. Proton-conducting ceramic fuel cells: scale up and stack integration. J Power Sources. 2021; 482: 228868.

[160] Zhu Y, Zhou W, Ran R, Chen Y, Shao Z, Liu M. Promotion of oxygen reduction by exsolved silver nanoparticles on a perovskite scaffold for low-temperature solid oxide fuel cells. Nano Lett. 2016; 16(1): 512-518.

[161] Kim JH, Kim JK, Seo HG, et al. Ex-solved Ag nanocatalysts on a Sr-free parent scaffold authorize a highly efficient route of oxygen reduction. Adv Funct Mater. 2020; 30(27): 2001326.

[162] Guo Y, Ran R, Shao Z, Liu S. Effect of Ba nonstoichiometry on the phase structure, sintering, electrical conductivity and phase stability of Ba_1±xCe_0.4Zr_0.4Y_0.2O_3−δ (0 ≤ x ≤ 0.20) proton conductors. Int J Hydrog Energy. 2011; 36(14): 8450-8460.

[163] Ge L, Zhou W, Ran R, et al. Properties and performance of A-site deficient (Ba_0.5Sr_0.5)_1−xCo_0.8Fe_0.2O_3−δ for oxygen permeating membrane. J Membr Sci. 2007; 306(1-2): 318-328.

[164] Hardy JS, Stevenson JW, Singh P. Effects of Humidity on Solid Oxide Fuel Cell Cathodes. Pacific Northwest National Lab (PNNL); 2015.

[165] Ebbesen SD, Graves C, Hauch A, Jensen SH, Mogensen M. Poisoning of solid oxide electrolysis cells by impurities. J Electrochem Soc. 2010; 157(10): B1419.

[166] Lai SY, Ding D, Liu M, Liu M, Alamgir FM. Operando and in situ x-ray spectroscopies of degradation in La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ thin film cathodes in fuel cells. ChemSusChem. 2014; 7(11): 3078-3087.

[167] Benson SJ, Waller D, Kilner JA. Degradation of La_0.6Sr_0.4Fe_0.8Co_0.2O_3−δ in carbon dioxide and water atmospheres. J Electrochem Soc. 1999; 146(4): 1305-1309.

[168] Zhou Y, Liu E, Chen Y, et al. An active and robust air electrode for reversible protonic ceramic electrochemical cells. ACS Energy Lett. 2021; 6(4): 1511-1520.

[169] Zhai S, Xie H, Cui P, et al. A combined ionic Lewis acid descriptor and machine-learning approach to prediction of efficient oxygen reduction electrodes for ceramic fuel cells. Nat Energy. 2022; 7(9): 866-875.

[170] Bello IT, Guan D, Yu N, et al. Revolutionizing material design for protonic ceramic fuel cells: bridging the limitations of conventional experimental screening and machine learning methods. Chem Eng J. 2023; 477: 147098.

[171] Wang N, Yuan B, Tang C, et al. Machine-learning-accelerated development of efficient mixed protonic-electronic conducting oxides as the air electrodes for protonic ceramic cells. Adv Mater. 2022; 34(51): 2203446.

[172] Han X, Ling Y, Yang Y, et al. Utilizing high entropy effects for developing chromium-tolerance cobalt-free cathode for solid oxide fuel cells. Adv Funct Mater. 2023; 33(43): 2304728.

[173] Nicollet C, Toparli C, Harrington GF, Defferriere T, Yildiz B, Tuller HL. Acidity of surface-infiltrated binary oxides as a sensitive descriptor of oxygen exchange kinetics in mixed conducting oxides. Nat Catal. 2020; 3(11): 913-920.

[174] Hu X, Zhou Y, Luo Z, et al. Data-driven discovery of electrode materials for protonic ceramic cells. Energy Environ Sci. 2024; 17(23): 9335-9345.

[175] Liu Z, Tang Z, Song Y, et al. High-entropy perovskite oxide: a new opportunity for developing highly active and durable air electrode for reversible protonic ceramic electrochemical cells. Nano Lett. 2022; 14(1): 217.

[176] Cheng QY, Wang MF, Ni JJ, et al. High-entropy alloys for accessing hydrogen economy via sustainable production of fuels and direct application in fuel cells. Rare Metals. 2023; 42(11): 3553-3569.

[177] He F, Zhou Y, Hu T, et al. An efficient high-entropy perovskite-type air electrode for reversible oxygen reduction and water splitting in protonic ceramic cells. Adv Mater. 2023; 35(16): 2209469.

[178] Wang Y, Robson MJ, Manzotti A, Ciucci F. High-entropy perovskites materials for next-generation energy applications. Joule. 2023; 7(5): 848-854.

[179] Yang C, Li J, Yang C, et al. A highly active and robust air electrode for reversible protonic ceramic cells: advanced performance achieved by low-Lewis-acid-strength cation doping strategy. ACS Mater Lett. 2024; 6(8): 3540-3547.

[180] Seo HG, Staerz A, Kim DS, LeBeau JM, Tuller HL. Tuning surface acidity of mixed conducting electrodes: recovery of Si-induced degradation of oxygen exchange rate and area specific resistance. Adv Mater. 2023; 35(8): 2208182.

[181] Seo HG, Kim H, Jung W, Tuller HL. Reversal of chronic surface degradation of Sr(Ti, Fe)O₃ perovskite-based fuel cell cathodes by surface acid/base engineering. Appl Catal B Environ Energy. 2024; 355: 124172.

[182] Smith DW. An acidity scale for binary oxides. J Chem Educ. 1987; 64(6): 480.

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