Photoelectrochemical behaviors and photocatalytic activities of mixed CuO and CuFeO₂ films with Ti and Ni underlayers for CO₂ conversion

This study synthesizes heterojunction CuO and CuFeO₂ (CFO) films via electrodeposition on Ti and Ni-deposited transparent conducting substrates and examines their photoelectrochemical behavior and unassisted photocatalytic activities for CO₂ conversion in aqueous bicarbonate solutions at circumneutral pH. Deposition of 15 nm and 50 nm-thick metal layers increases the electrical conductivity of the substrate, improving the deposition kinetics of the CFO precursors and establishing firm contact between CFO and the substrate. CFO films with Ti and Ni underlayers (Ti/CFO and Ni/CFO) exhibit higher photocurrent generation than bare CFO, owing to the rapid charge transfer and low interfacial charge-transfer resistance. Despite comparable apparent solar-to-chemical conversion (STC) efficiencies (∼1%), the C1 chemical (formate) is the sole product in the bare CFO film, whereas mixed C1–C4 chemicals are produced in Ti- and Ni-underlayered CFO films. When estimated based on transmitted light, the Ti/CFO and Ni/CFO films exhibit STCs of ∼7% and 3%, respectively.