Construction of Co1-xZnxFe2xGa2-2xO4 (0<x≤0.6) Solid Solutions for Improving Solar Fuels Production in Photocatalytic CO2 Reduction by H2O Vapour

Abstract

Solid solutions are garnering substantial attention in the realm of solar energy utilization due to their tunable electronic properties, encompassing band edge positions and charge-carrier mobilities. In this study, we designed and synthesized Co_1-xZn_xFe_2xGa_2-2xO₄ (0<x≤0.6) as a photocatalyst for CO₂ conversion using H₂O. Careful optical and photo/electrochemical characterizations unveiled that the relative content of CoGa₂O₄ and ZnFe₂O₄ not only substantially influences light absorption in the full solar spectrum but also modulates valence and conduction band positions. We thoroughly assessed the photocatalytic activity of Co_1-xZn_xFe_2xGa_2-2xO₄ and found that when x=0.35, the solid-solution catalyst achieved a remarkable CO₂ reduction rate to CH₄ and CO (31.5 μmol g^-1 h^-1). Furthermore, this optimized solid-solution catalyst demonstrated impressive photostability. Characterization and DFT calculations revealed that the formation of a solid solution not only reduces the band gap and promotes the separation of electron-hole pairs to accelerate efficient CO₂ photoreduction, but also the introduction of more FeO₆ octahedral active sites in Co_1-xZn_xFe_2xGa_2-2xO₄ solid solutions enhanced the effective photoreduction of CO₂. This design results in high conversion efficiencies for producing solar fuels through CO₂ reduction with H₂O.

Keywords: CO2 conversion; Co1-xZnxFe2xGa2–2xO4; Solid solution; molten salts; photosynthesis.