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　Co1-xZnxFe2xGa2–2xO4　(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　Co1-xZnxFe2xGa2–2xO4　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　Co1-xZnxFe2xGa2–2xO4　solid　solutions　enhanced　the　effective　photoreduction　of　CO2.　This　design　results　in　high　conversion　efficiencies　for　producing　solar　fuels　through　CO2　reduction　with　H2O.　©　2024　Wiley-VCH　GmbH.