Photo-enhanced Co single-atom catalyst with a staggered p-n heterojunction: unraveling its high oxygen catalytic performance in zinc-air batteries and fuel cells

The sluggish kinetics of the oxygen reduction reaction (ORR) and high over potential of oxygen evolution reaction (OER) are big challenges in the development of high-performance zinc-air batteries (ZABs) and fuel cells. In this work, we report a rational design and a simple fabrication strategy of a photo-enhanced Co single-atom catalyst (SAC) comprising g-C₃N₄ coupled with cobalt-nitrogen-doped hierarchical mesoporous carbon (Co-N/MPC), forming a staggered p-n heterojunction that effectively improves charge separation and enhances electrocatalytic activity. The incorporation of Co SACs and g-C₃N₄ synergistically optimizes the photogenerated electron-hole pair separation, significantly boosting the intrinsic ORR-OER duplex activity. Under illumination, g-C₃N₄@Co-N/MPC exhibits an outstanding ORR half-wave potential (E_1/2) of 0.841 V (vs. RHE) in 0.1 mol L^–1 KOH and a low OER overpotential of 497.4 mV (vs. RHE) at 10 mA cm^–2 in 1 mol L^–1 KOH. Notably, the catalyst achieves an exceptional peak power density of 850.7 mW cm^–2 in ZABs and of 411 mW cm^–2 even in H₂-air fuel cell. In addition, g-C₃N₄@Co-N/MPC-based ZABs also show remarkable cycling stability exceeding 250 h. The advanced photo-induced charge separation at the p-n heterojunction facilitates faster electron transfer kinetics, and the mass transport owing to hierarchical mesoporous structure of Co-N-C, thereby reducing the overpotential and enhancing the overall energy conversion efficiency. This work provides a new perspective on designing next-generation of single-atom dispersed oxygen reaction catalysts, paving the way for high-performance photo-enhanced energy storage and conversion systems.