Germanium and iron double-substituted ZnGa2O4 solid-solution photocatalysts with modulated band structure for boosting photocatalytic CO2 reduction with H2O

Abstract

The conversion of CO2 into renewable fuels by artificial photosynthesis is an attractive solution for storing solar energy in the form of chemical fuel. Herein, we presented a general molten-salt route to synthesize spinel germanium and iron double-substituted ZnGa2O4 solid solutions. Introducing ZnFe2O4 and Zn2GeO4 into ZnGa2O4 can effectively expand the light-harvesting wavelength range to improve the ability of photocatalyst in CO2 reduction and H2O oxidation. The solid solutions provide a larger effective mass of holes compared with electrons through the introduction of Fe3d, Ge4s and Ge4p orbitals according to DFT analysis. This leads to a great difference in the mobility between the electrons and holes to lessen the electron–hole recombination rate, and enhance the conversion of CO2 and H2O in kinetics. This approach is developed to achieving smaller bandgap values and a closer bracketing of the CO2/reduced-H2O/oxidized redox couples to drive the overall conversion of CO2 and H2O.