A perspective on cathode materials for proton-conducting solid oxide fuel cells

Proton-conducting solid oxide fuel cells (PCFCs) offer enhanced operational efficiencies at low and intermediate temperatures (400-700 degrees C) compared to traditional oxygen-ion conducting solid oxide fuel cells, making them as highly attractive electrochemical devices. PCFCs prevent fuel dilution by efficiently converting hydrogen or hydrogen-containing fuels into electrical energy, producing water at the cathode. Nevertheless, reducing the operating temperature can lead to decreased ion mobility, reduced electrode reaction kinetics, and increased losses at the electrodes, particularly the cathode. This underscores the necessity to strategically design highperformance cathode materials and deepen the understanding of the conduction mechanisms underpinning PCFCs. This review comprehensively examines oxides employed in the PCFC cathode domain, with a special focus on composites exhibiting triple conduction properties (i.e., H+/O2-/e-). To guide future material development, the manuscript highlights proton absorption and conduction mechanisms, as well as explores the relationship between the microstructure and the corresponding properties, and evaluates the chemical stability of the cathode material for PCFC in environments containing H2O-CO2. By comparing the impacts of various types of cathode materials on application performance, the study establishes a robust foundation for material selection and optimization. Finally, the potential for developing high-performance PCFCs is projected.