Synthesis of Aliphatic Acids from CO2 and Water at Efficiencies Close to the Photosynthesis Limit Using Mixed Copper and Iron Oxide Films

The photocatalytic conversion of CO2 and water into value-added chemicals remains a great challenge. This study shows that uniformly mixed copper and iron oxide (CuO/CuFeO2; CFO) bulky heterojunction films are capable of converting CO2 and water into C1–C6 aliphatic acid anions and O2 at a solar-to-chemical energy conversion (STC) efficiency close to 3% under simulated sunlight in the absence of any sacrificial chemicals or electrical biases. When the CFO film is simply wired to a Pt foil, C1 (formate, with selectivity of 100%) and O2 are produced at a near-stoichiometric ratio at an STC efficiency of ∼5% via the Z-scheme charge transfer mechanism. The CFO films are durable over 1 week and recyclable over 5 weeks under continuous irradiation. The addition of chloride enhances formate production, with an STC efficiency of 10%, while inhibiting the deformation of CFOs. Density functional theory computations support the observed selectivity and durability.