Highly durable Cu–N–C active sites towards efficient oxygen reduction for zinc-air battery: Carbon matrix effect, reaction mechanism and pathways

The thorough understanding of ORR mechanism provides insights into the design of efficient ORR catalysts. Despite remarkable progress has been made in the development of Cu–N–C ORR catalysts, fundamental understanding of molecular governing factors is still lacking. The carbon matrix with varying π-electron delocalization degree can modulate electron density at the metal ion center rather than merely acting as the electron-conducting path. A volcano relationship is established between oxygen-reduction intrinsic activity and full-width at half-maxima (FWHM) of C 1s photoemission spectra (depicting electron donating/withdrawing capability of carbon matrix to metal ion center). The mechanistic origin of ORR on carbon matrix, N–C sites, and Cu sites in Cu–N–C catalyst in different reaction regions is also illuminated. This work will be likely to offer a new insight in the development of more selective and durable Cu–N–C catalysts for zinc-air batteries.