A surface regulation strategy to fabricate Cu-Nx sites of high homogeneity with countable activity towards oxygen reduction

Carbon catalysts with transition metal atoms anchored via nitrogen coordination have emerged as promising alternatives to Pt in catalyzing oxygen reduction reaction (ORR). However, the intangible evolution of structure in popular synthetic routes containing pyrolysis leads to discrete and irregular M-Nx sites, resulting in limited descriptors and thus ambiguous understandings of structure-activity relationships. We report here a facile method to synthesize Cu-Nx sites of high homogeneity anchored on carbon substrates through deposition and carbonization of glycoluril on metallic copper surface. The Cu-Nx sites take shape under the surface regulation of metallic copper and preferentially exposed after removal of excess Cu. The optimal catalyst presents efficient activity towards ORR with a half-wave potential of 0.84 V (vs. RHE). More importantly, linear relationships over the catalyst between current densities and electrochemical active surface areas (ECSAs) are derived, suggesting activities countable by ECSAs. The correlation clearly demonstrates the high homogeneity and catalytic accessibility of surface-regulated Cu-Nx sites. The well-elucidated structure-activity relationship identifies Cu-Nx sites as originates of catalytic ORR at an experimental level and sheds light on rational engineering of catalysts containing M-Nx sites.