Artificial Photosynthesis of H2O2 through Reversible Photoredox Transformation between Catechol and o-Benzoquinone on Polydopamine-Coated CdS

Artificial photosynthesis of H2O2 from water and O2 only is a prospective alternative to the industrial anthraquinone process, which requires the development of cheap, efficient, and stable photocatalysts working without sacrificial reagents. Inspired by the industrial strategy, polydopamine (PDA)-coated CdS was designed for the photosynthesis of H2O2 and achieved a yield of 3.84 mM in 24 h under visible light from water and dioxygen, which is 13.7 times higher than that of CdS. The dehydrogenation of catechol to o-benzoquinone in PDA is coupled with two-electron O2 reduction to produce H2O2, while the photoreductive hydrogenation of o-benzoquinone regenerates catechol in PDA concurrently. The reversible redox transformation between catechol and the o-benzoquinone moiety in PDA under visible light markedly increases both the production yield and the selectivity of H2O2 (from 30% on CdS to 82% on CdS–PDA). In addition, PDA coating increases the O2 adsorption capacity, inhibits H2O2 decomposition, and enhances the stability of CdS against photocorrosion. This structural design enables artificial photosynthesis of H2O2 without sacrificial reagents.