A facile synthesis of CuFeO₂ and CuO composite photocatalyst films for the production of liquid formate from CO₂ and water over a month

The development of low-cost photocatalysts capable of selectively producing liquid chemicals from CO₂ and water with efficiency and durability comparable to typical photosynthetic values remains a great challenge. Herein, we report a facile, environmentally benign synthesis of CuFeO₂ and CuO binary films by electrodeposition, and demonstrate that these binary films produce only liquid formate from aqueous CO₂ at ∼1% energy efficiency, while driving O₂ evolution from water on a wired Pt plate under continuous irradiation of simulated sunlight (AM 1.5G; 100 mW cm^-2) over 24 h. The formate production is confirmed by quantitative analysis of H¹³CO₂^- produced from ¹³CO₂. A time-resolved photoluminescence study reveals the sub-nanosecond charge transfer in binary CuFeO₂ and CuO films, wherein the aqueous CO₂ is adsorbed. An as-synthesized photocatalyst film with a three dimensional, double layer configuration shows the continued production of formate for over 17 d. However, the crystalline structure and elemental state of the used photocatalysts undergo gradual chemical reduction. Such a deformation can be thermally healed by recycling the weekly used samples via oxidative annealing. Thus, a single photocatalyst sample produces formate continuously for 35 d.