Undervalued role of metal-carbon junction in selective generation of H2O2: An example of the zinc-carbon junction edge providing asymmetric active sites for efficient oxygen reduction

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The spontaneous oxygen reduction is a potential technology for in-situ H2O2 production, which gets rid of the dependence on electricity and solar energy. Previous some metal–carbon compounds reported are feasible to trigger oxygen reduction. These reports always claim the high H2O2 generation ability of metal–carbon composites, while rarely discuss the contribution of carbon and the carbon–metal junction to the oxygen reduction process. Inspired by the dual active sites, we infer that the role of interfacial carbon in metal–carbon composites is underestimated. By a heat treatment of the co-precipitate of zinc and glucose, the Zn-C junction is constructed in Zn-gc to achieve a spontaneous selective reduction of O2 to H2O2. The Zn-C interface edge is active site, where an asymmetric activation is achieved by bonding two O atoms from O2 to C and Zn, respectively. The Zn traction to one of the O atoms is mainly in xy plane, while the C traction to the other O atom is parallel to z-axis. The yield of H2O2 produced per gram of Zn increases from 27.89 mg to 122.21 mg, an improvement of 4.38 times. And the inertness of Zn and its oxygen-containing compounds towards H2O2 enables Zn-gc/O2 system to stabilize H2O2 over a long period of time. This work reveals the crucial role of neglected junction interfaces in oxygen reduction reactions in metal–carbon composites.