Delafossite CuFeO2 Photocathodes Grown by Direct Liquid Injection Chemical Vapor Deposition for Efficient Photoelectrochemical Water Reduction

Abstract

Delafossite CuFeO2 (CFO) thin film photocathodes are fabricated by a direct liquid injection chemical vapor deposition (DLI-CVD) technique. CFO photocathodes grown on fluorine-doped tin oxide (FTO) substrates are investigated for photoelectrochemical (PEC) water reduction for hydrogen generation. CFO photocathode fabricated at 550°C with an optimal film thickness of ∼150 nm exhibit a maximum photocurrent density of ∼0.71 mA cm−2 at 0.6 V vs. RHE under a standard 1 SUN illumination (AM 1.5G, 100 mW cm−2) in 1 M NaOH electrolyte (pH 13.5) under ambient conditions. The performance is further improved in a O2-saturated solution yielding higher photocurrent density as high as ∼1.3 mA cm−2 at 0.6 V vs. RHE, with O2 serving as a sacrificial agent. CFO film absorbs over the entire visible wavelength range and delivers maximum incident photon-to-current conversion efficiency (IPCE) values of ∼18% and ∼28% at 0.6 V vs. RHE (at 400 nm) in unpurged and O2-saturated NaOH solution, respectively. The enhancement in PEC and IPCE with O2 purging is due to combined effects of water reduction and oxygen reduction reaction (ORR). Mott-Schottky study demonstrate an improvement in onset potential with higher carrier density for the CFO films as compared to previous reports. Overall, the enhanced PEC performance is attributed to the high-quality growth of crystalline CFO thin films on FTO substrates by DLI-CVD technique, exhibiting good stability in different electro-chemical environments.