Accelerating charge separation in p-n heterojunction photocathode for photoelectrochemical oxygen reduction and evolution in photo-enhanced zinc-air battery

For the first time, we constructed a band-matched ZnO/NiO staggered p-n heterojunction photoelectrochemical (PEC) catalyst with superior charge separation and transfer efficiency to optimize the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics demands of a photo-enhanced zinc-air battery (PZAB). The ingenious design of heterojunction architecture effectively stimulates an internal self-built electric field (BEF), thus accelerating charge separation and migration during PEC catalysis. Upon illumination, the photocathode not only endows a promoted PEC catalytic competence to drive ORR and OER, but also reduces the charge–discharge voltage gap of PZAB. Density functional theory (DFT) calculations further disentangled the PEC catalysis activity origins by substantiating the strongly decreased Gibbs free energy potently for generating the essential intermediates *OH and *OOH during ORR and OER, respectively, and visualized the charge densities in photocathode to illustrate the authentic separation of photogenerated carriers. Remarkably, our work experimentally and theoretically sheds lights on engineering innovative and efficient bifunctional PEC catalysts to drive PZABs with photo-enhancement.