Electrosynthesis of hydrogen peroxide (H₂O₂) through oxygen reduction reaction (ORR) is an environment-friendly and sustainable route for obtaining a fundamental product in the chemical industry. Co-N₄ single-atom catalysts (SAC) have sparkled attention for being highly active in both 2e^- ORR, leading to H₂O₂ and 4e^- ORR, in which H₂O is the main product. However, there is still a lack of fundamental insights into the structure-function relationship between CoN₄ and the ORR mechanism over this family of catalysts. Here, by combining theoretical simulation and experiments, we unveil that pyrrole-type CoN₄ (Co-N SAC_Dp) is mainly responsible for the 2e^- ORR, while pyridine-type CoN₄ catalyzes the 4e^- ORR. Indeed, Co-N SAC_Dp exhibits a remarkable H₂O₂ selectivity of 94% and a superb H₂O₂ yield of 2032 mg for 90 h in a flow cell, outperforming most reported catalysts in acid media. Theoretical analysis and experimental investigations confirm that Co-N SAC_Dp─with weakening O₂/HOO* interaction─boosts the H₂O₂ production.

Single-site cocatalysts engineered on supports offer a cost-efficient pathway to utilize precious metals, yet improving the performance further with minimal catalyst loading is still highly desirable. Here we have conducted a photochemical reaction to stabilize ultralow Pt co-catalysts (0.26 wt%) onto the basal plane of hexagonal ZnIn₂S₄ nanosheets (Pt_SS-ZIS) to form a Pt-S₃ protrusion tetrahedron coordination structure. Compared with the traditional defect-trapped Pt single-site counterparts, the protruding Pt single-sites on h-ZIS photocatalyst enhance the H₂ evolution yield rate by a factor of 2.2, which could reach 17.5 mmol g⁻¹ h⁻¹ under visible light irradiation. Importantly, through simple drop-casting, a thin Pt_SS-ZIS film is prepared, and large amount of observable H₂ bubbles are generated, providing great potential for practical solar-light-driven H₂ production. The protruding single Pt atoms in Pt_SS-ZIS could inhibit the recombination of electron-hole pairs and cause a tip effect to optimize the adsorption/desorption behavior of H through effective proton mass transfer, which synergistically promote reaction thermodynamics and kinetics.