We report facile synthesis of low-band-gap mesoporous C4 N particles and their use as responsive bifunctional oxygen catalysts for visible-light-sensitive (VLS) rechargeable Zn-air battery (RZAB) and polymer-air battery (RPAB). Compared to widely studied g-C3 N4 , C4 N shows a smaller band gap of 1.99 eV, with a larger photocurrent response, and it can function as visible-light-harvesting antenna and bifunctional oxygen reduction/evolution (ORR/OER) catalysts, enabling effective photocoupling to tune oxygen catalysis. The C4 N-enabled VLS-RZAB displays a low charge voltage of 1.35 V under visible light, which is below the theoretical RZAB voltage of 1.65 V, corresponding to a high energy efficiency of 97.78 %. Pairing a C4 N cathode with a polymer anode also endows an VLS-RPAB with light-boosted charge performance. It is revealed that the ORR and OER active sites in C4 N are separate carbon sites near pyrazine-nitrogen atoms and photogenerated energetic holes can activate OER for improved reaction kinetics.
Keywords: oxygen evolution reaction; oxygen reduction reaction; photocoupled batteries; rechargeable air batteries; solar energy conversion and storage.
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