From catalyst structure design to electrode fabrication of platinum-free electrocatalysts in proton exchange membrane fuel cells: A review

[Display omitted] The development of low-cost fuel cell technology has involved substantial research on platinum-free or non-platinum group metal (non-PGM) catalysts for oxygen reduction reactions (ORR) in proton exchange membrane fuel cells. However, due to macroscale degradation and flooding issues in fuel cell systems, catalyst development has faced significant challenges in rapid active site degradation over a short time. This review presents the impacts of the non-PGM catalyst structure on the ORR activity and single-cell performance. A balance in the micropores, mesopores and macropores is sought to ensure high accessibility to the active sites, a high active site density, and good water management at the electrode layer to prevent active site blockage. The unsatisfactory single-cell performance of non-PGM electrodes also potentially arises from the conventional catalyst ink-casting technique. This review also provides insight into the necessary strategies for producing non-PGM MEAs via proper porous architecture and innovative catalyst casting techniques to develop promising low-cost PEMFC technology.