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

The conversion of CO 2 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 ZnGa 2 O 4 solid solutions. Introducing ZnFe 2 O 4 and Zn 2 GeO 4 into ZnGa 2 O 4 can effectively expand the light-harvesting wavelength range to improve the ability of photocatalyst in CO 2 reduction and H 2 O 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 CO 2 and H 2 O in kinetics. This approach is developed to achieving smaller bandgap values and a closer bracketing of the CO 2 /reduced-H 2 O/oxidized redox couples to drive the overall conversion of CO 2 and H 2 O.