Mapping Transition Metal-Nitrogen-Carbon Catalysts Performance on the Critical Descriptors Diagram

PGM-free electrocatalysts, and in particular transition metal-nitrogen-carbon (M-N-C) catalysts are becoming interesting candidates as cheap alternatives to Pt-based catalysts for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFC). Unified activity-stability correlations are needed in order to provide practical guidelines for a rational catalyst design. A discussion of different characterization techniques for studying possible activity descriptors is presented, with a specific focus on active-site density (SD) and turn-over frequency (TOF). These descriptors will be associated to the morphology of the various M-N-C electrocatalysts investigated in the recent literature. The underlined correlation for this class of PGM-free electrocatalysts offers important insights required for the development of the next-generation of catalytic materials with enhanced stability, that can solve the main activity and durability barriers needed for the replacement of Pt-based counterparts.