Production of hydrogen peroxide as a sustainable solar fuel from water and dioxygen

Hydrogen peroxide was produced as a solar fuel from water and dioxygen using solar energy by combination of a water oxidation catalyst and a photocatalyst for two-electron reduction of O-2 in acidic aqueous solutions. Photocatalytic production of H2O2 occurred under photoirradiation of [Ru-II(Me(2)phen)(3)](2+) (Me(2)phen = 4,7-dimethyl-1,10-phenanthroline) used as a photocatalyst with visible light in the presence of Ir(OH)(3) acting as a water oxidation catalyst in an O-2-saturated H2SO4 aqueous solution. Photoinduced electron transfer from the excited state of [Ru-II(Me(2)phen)(3)](2+) to O-2 results in the formation of [Ru-III(Me(2)phen)(3)](3+) and a superoxide radical anion (O-2(center dot-)) which is protonated to produce H2O2 via disproportionation of HO2 center dot in competition with back electron transfer (BET) from O-2(center dot-) to [Ru-III(Me(2)phen)(3)](3+). [Ru-III(Me(2)phen)(3)](3+) oxidises water with the aid of catalysis of Ir(OH) 3 to produce O-2. The photocatalytic reactivity of H2O2 production was improved by replacing Ir(OH)(3) nanoparticles by [Co-III(Cp*)(bpy)(H2O)](2+) in the presence of Sc(NO3)(3) in water. The optimised quantum yield of the photocatalytic H2O2 production at lambda = 450 nm was determined using a ferrioxalate actinometer to be 37%. The value of conversion efficiency from solar energy to chemical energy was also determined to be 0.25%.