Capturing Visible Light in Low‐Band‐Gap C4N‐Derived Responsive Bifunctional Air Electrodes for Solar Energy Conversion and Storage

Abstract We report facile synthesis of low‐band‐gap mesoporous C 4 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‐C 3 N 4 , C 4 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 C 4 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 C 4 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 C 4 N are separate carbon sites near pyrazine‐nitrogen atoms and photogenerated energetic holes can activate OER for improved reaction kinetics.