Solar-Driven Production of Hydrogen Peroxide from Water and Dioxygen.

Hydrogen peroxide, which is a green oxidant and fuel, is produced by a two-electron/two-proton reduction of dioxygen, two-electron/two-proton oxidation of water, or a combination of four-electron/four-proton or/and two-electron/two-proton oxidation of water and two-electron/two-proton reduction of dioxygen. There are many reports on electrocatalysts for selective two-electron/two-proton reduction of dioxygen to produce hydrogen peroxide instead of four-electron/four-proton reduction of dioxygen to produce water. As compared with the two-electron/two-proton reduction of dioxygen to produce hydrogen peroxide, fewer catalysts are known for the selective two-electron/two-proton oxidation of water to produce hydrogen peroxide instead of four-electron/four-proton oxidation of water to evolve dioxygen. Thus, solar-driven production of hydrogen peroxide mainly consists of the catalytic four-electron/four-proton oxidation of water and the catalytic two-electron/two-proton reduction of dioxygen. The overall reaction is the solar-driven oxidation of water by dioxygen to produce hydrogen peroxide. Either or both the four-electron/four-proton or/and the two-electron/two-proton oxidation of water and the two-electron/two-proton reduction of dioxygen requires photocatalysts. The yield of hydrogen peroxide is improved when the compartment for the photocatalytic four-electron/four-proton or/and two-electron/two-proton oxidation of water is separated from that for the catalytic two-electron/two-proton reduction of dioxygen using a two-compartment cell separated by a membrane. The overall solar-driven oxidation of water by dioxygen, which is the greenest oxidant, to produce hydrogen peroxide can be combined with catalytic oxidation of various substrates by hydrogen peroxide.