Introducing highly polarizable cation in M-N-C type catalysts to boost their oxygen reduction reaction performance

The metal-nitrogen-carbon (M-N-C) type oxygen reduction reaction (ORR) catalysts are promising for hydroxide exchange membrane fuel cells, but catalysts with further improved performance are challenging. Here, we report the efficient improvement of the ORR activity of M-N-C catalysts by employing highly polarizable metal cation Ag⁺. Ag, Fe single atomic sites embedded in concave nitrogen doped carbon (Ag₁Fe₁/CNC) is successfully synthesized and shows high performance towards ORR, indicating by both the ultra-high half-wave potential of 0.917 V and membrane electrolyte assembly performance of peak power density up to 1.26 W cm⁻². The binding energy of the ORR intermediates on the highly polarizable Ag site in Ag₁Fe₁/CNC was significantly tuned by the adjacent Fe site by more than 0.2 eV, and thus leading to a low theoretical ORR overpotential of only 0.398 V. The employment of the highly polarizable metal cation brings a novel and efficient approach to construct highly active catalysts.