1e:T43c,Hydrogen peroxide (H₂O₂) synthesis generally requires substantial postreaction purification. Here, we report a direct electrosynthesis strategy that delivers separate hydrogen (H₂) and oxygen (O₂) streams to an anode and cathode separated by a porous solid electrolyte, wherein the electrochemically generated H⁺ and HO₂ ^- recombine to form pure aqueous H₂O₂ solutions. By optimizing a functionalized carbon black catalyst for two-electron oxygen reduction, we achieved >90% selectivity for pure H₂O₂ at current densities up to 200 milliamperes per square centimeter, which represents an H₂O₂ productivity of 3.4 millimoles per square centimeter per hour (3660 moles per kilogram of catalyst per hour). A wide range of concentrations of pure H₂O₂ solutions up to 20 weight % could be obtained by tuning the water flow rate through the solid electrolyte, and the catalyst retained activity and selectivity for 100 hours.1f:T510,Synthesizing H₂ O₂ from water and air via a photocatalytic approach is ideal for efficient production of this chemical at small-scale. However, the poor activity and selectivity of the 2 e^- water oxidation reaction (WOR) greatly restricts the efficiency of photocatalytic H₂ O₂ production. Herein we prepare a bipyridine-based covalent organic framework photocatalyst (denoted as COF-TfpBpy) for H₂ O₂ production from water and air. The solar-to-chemical conversion (SCC) efficiency at 298 K and 333 K is 0.57 % and 1.08 %, respectively, which are higher than the current reported highest value. The resulting H₂ O₂ solution is capable of degrading pollutants. A mechanistic study revealed that the excellent photocatalytic activity of COF-TfpBpy is due to the protonation of bipyridine monomer, which promotes the rate-determining reaction (2 e^- WOR) and then enhances Yeager-type oxygen adsorption to accelerate 2 e^- one-step oxygen reduction. This work demonstrates, for the first time, the COF-catalyzed photosynthesis of H₂ O₂ from water and air; and paves the way for wastewater treatment using photocatalytic H₂ O₂ solution.20:T4c3,Photocatalytic selective oxidation reactions hold great promise for the design of high-value-added organic intermediates, but many of these reactions suffer from low conversion efficiency and selectivity due to uncontrollable oxidation processes. In view of using photogenerated reactive oxygen species as the key oxidant in a selective oxidation reaction, we propose that a highly selective oxidation reaction can be achieved by modulating the corresponding photocatalytic molecular oxygen (O₂) activation processes. Using cubic indium sulfide (β-In₂S₃) nanosheets as a model system, we show that the charge carriers involved in O₂ activation can be optimized with the introduction of surface S vacancies. Benefiting from the enhanced charge separation and transfer processes, the In₂S₃ nanosheets with S vacancies could simultaneously activate O₂ into superoxide radicals via electron transfer under visible-light irradiation to display outstanding activity for the selective oxidation of alcohols to aldehydes with high conversion and selectivity. This study offers a new strategy to optimize photocatalytic selective oxidation reactions.

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