Oxidase-Inspired Selective 2e/4e Reduction of Oxygen on Electron-Deficient Cu

Development of low-cost and efficient (electro)catalysts with tunable 2e/4e oxygen reduction reaction (ORR) selectivity toward energy conversion, biomimetic catalysis, and biosensing has attracted growing interest. Herein, we reported that carbon nanohybrids with O- or N-coordinated Cu (Cu–OC or Cu–NC) showed superior activity for 2e and 4e electrocatalytic ORR with selectivities of 84.0% and 97.2%, respectively. Experimental evidence demonstrated that the strong electron-rich O-doped carbon in Cu–OC donated electrons to Cu2+, weakening the binding strength of H2O2 at Cu–O centers and facilitating the 2e ORR pathway for selective production of H2O2. However, the poor electron-donor ability of the N-doped carbon in Cu–NC made Cu–N sites more electron deficient due to the reduced electron transfer from N-doped carbon to Cu2+, promoting 4e ORR by enhancing adsorption of O2 and the ORR intermediates. The high 4e ORR activity of Cu–NC rendered its potential for application in a Zn–air battery and oxidase-mimicking activity for 3,3′,5,5′-tetramethylbenzidine (TMB) and ascorbic acid (AA) oxidation. The maximal velocity (Vmax) of TMB and AA oxidation over Cu–NC was higher than some natural oxidases and noble-metal-based artificial enzymes. The lower activation energy for AA oxidation over Cu–NC resulted in a 263-fold higher oxidative rate than TMB, further prompting nonenzymatic sensing of AA by the competitive oxidation strategy.