Synthesizing H2O2 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 H2O2 production. Herein we prepare a bipyridine‐based covalent organic framework photocatalyst (denoted as COF‐TfpBpy) for H2O2 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 H2O2 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 H2O2 from water and air; and paves the way for wastewater treatment using photocatalytic H2O2 solution.

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The application of Cu2O catalysts in CO2 photocatalytic reduction has attracted much attention due to the capacity to generate high-calorific-value hydrocarbon fuels with pre-eminent selectivity. However, the origin of the high selectivity remains unclear. In this study, the (111) facet of Cu2O was verified as the origin of selectivity for CH4 (the simplest hydrocarbon) formation by comparing the photocatalytic CO2 reduction behaviors of Cu2O catalysts with varied active facets. Results showed that Cu2O-100 produced negligible CH4 (selectivity = 0%), whereas the yield of CH4 on Cu2O-111 was 12.24 μmol·g–1·h–1 with a substantially high selectivity of 91.4%. After decoration with zero-valent copper on the surface of Cu2O-111 (Cu2O-111-Cu0), the yield of CH4 reached 78.4 μmol·g–1·h–1, affording a selectivity of CH4 as high as 97%. In situ FT-IR and theoretical calculations showed that the (111) facet has stronger CO absorption capacity and electron reduction capacity for highly selective photocatalytic CO2 conversion. Moreover, the presence of Cu0 on the (111) facet could accelerate the carrier separation efficiency, thus providing more electrons for efficient hydrocarbon formation. This work provides a promising idea to design Cu2O catalysts for the conversion of CO2 into high value-added hydrocarbon products with high activity and selectivity.

Hydrogen peroxide (H2O2) is an important green oxidizing agent for environmental protection and chemical production. In comparison to the traditional anthraquinone method, photosynthesis is a green and energy‐saving process for H2O2 production. To improve the stability and practical application value of the H2O2 synthesized by photocatalysis, the H2O2 photosynthesis should be conducted in pure water without involving any sacrificial reagents. In this regard, organic semiconducting catalysts pose as a suitable candidate for photocatalytic H2O2 synthesis owing to their metal‐free nature to prevent H2O2 decomposition by the metal ions. In this Perspective, the H2O2 photosynthesis history is firstly introduced, followed by a review of the organic semiconductor photocatalysts reported to date. Finally, the main problems to thwart the advances of current pure H2O‐to‐H2O2 photosynthesis are discussed, followed by proposed solutions to address these issues in order to pave new ways for the development of highly efficient metal‐free organic photocatalysts for sustainable pure H2O‐to‐H2O2 conversion.

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