Multiscale cathode design for high-temperature proton exchange membrane fuel cells

High temperature proton exchange membrane fuel cells (HT-PEMFCs) are highly promising energy conversion devices featuring the benefits of their superior reaction kinetics, simplified water and thermal management systems, tolerance to CO-containing reactant gases, and being compatible with hydrogen production via industrial fuel reforming processes. However, due to the phosphoric acid (PA)-doped membranes being the primary proton exchange membranes (PEMs) used in HT-PEMFCs, the PA leaching from the membrane during the operation degrades platinum (Pt)-based oxygen reduction reaction (ORR) catalysts and the cathode catalyst layer, causing insufficient performance of HT-PEMFCs, which hinders their application. Although extensive research has been conducted to enhance the activity and durability of HT-PEMFCs, there remains a significant gap toward practical implementation, which stems from incomplete fundamental understanding of atomic-scale catalysts, reaction interfacial kinetics, and catalyst layer structure engineering. To fill the aforementioned research gap, this review summarizes recent developments in cathode catalysts, catalytic interface, and catalyst layers from a multiscale view of HT-PEMFCs. Beginning with the fundamental principles, the theoretical insights into PA-induced catalyst poisoning and catalyst layer degradation are first provided. Innovative design in ORR catalysts and catalytic interfaces with enhanced PA resistance and reaction kinetics is then presented. Additionally, approaches to optimizing the cathode catalyst layer are discussed from a practical application perspective. Finally, an outlook on the remaining challenges and prospects in this field is provided, aiming to facilitate the advancement of HT-PEMFCs.