Solar-to-chemical energy conversion is a challenging subject for renewable energy storage. In the past 40 years, overall water splitting into H2 and O2 by semiconductor photocatalysis has been studied extensively; however, they need noble metals and extreme care to avoid explosion of the mixed gases. Here we report that generating hydrogen peroxide (H2O2) from water and O2 by organic semiconductor photocatalysts could provide a new basis for clean energy storage without metal and explosion risk. We found that carbon nitride-aromatic diimide-graphene nanohybrids prepared by simple hydrothermal-calcination procedure produce H2O2 from pure water and O2 under visible light (λ > 420 nm). Photoexcitation of the semiconducting carbon nitride-aromatic diimide moiety transfers their conduction band electrons to graphene and enhances charge separation. The valence band holes on the semiconducting moiety oxidize water, while the electrons on the graphene moiety promote selective two-electron reduction of O2. This metal-free system produces H2O2 with solar-to-chemical energy conversion efficiency 0.20%, comparable to the highest levels achieved by powdered water-splitting photocatalysts.

Photocatalytic production of hydrogen peroxide (H2O2) from earth‐abundant water and O2 is a desirable artificial photosynthesis for solar fuel production. A metal‐free hybrid photocatalyst consisting of pyromellitic diimide‐doped carbon nitride (g‐C3N4/PDI), boron nitride (BN), and reduced graphene oxide (rGO) was prepared. The g‐C3N4/PDI‐BN‐rGO catalyst, when photoirradiated in water with O2 by visible light at room temperature, efficiently produces H2O2. The photoexcited g‐C3N4/PDI moiety transfers the conduction band electrons to rGO, leading to selective production of H2O2 via two‐electron reduction of O2 on the rGO surface. In contrast, the valence‐band holes photoformed on the g‐C3N4/PDI moieties are transferred to BN, leading to efficient oxidation of water. The electron–hole separation enhanced by the incorporation of rGO and BN significantly suppresses the charge recombination and exhibits high photocatalytic activity. The solar‐to‐chemical conversion (SCC) efficiency for H2O2 production on the hybrid catalyst is 0.27 %, which is higher than the highest efficiencies obtained by overall water splitting on powdered catalysts.

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