Mg-Doped CuFeO₂ Photocathodes for Photoelectrochemical Reduction of Carbon Dioxide

Mg-doped CuFeO₂ delafossite is reported to be photoelectrochemically active for CO₂ reduction. The material was prepared via conventional solid-state methods, and subsequently assembled into an electrode as a pressed pellet. Addition of a Mg²⁺ dopant is found to substantially improve the conductivity of the material, with 0.05% Mg-doped CuFeO₂ electrodes displaying photocathodic currents under visible irradiation. Photocurrent is found to onset at irradiation wavelengths of ~800 nm with the incident photon-to-current efficiency reaching a value of 14% at 340 nm using an applied electrode potential of –0.4 V vs SCE. Photoelectrodes were determined to have a –1.1 V vs SCE conduction band edge and were found capable of the reduction of CO₂ to formate at 400 mV of underpotential. The conversion efficiency is maximized at –0.9 V vs SCE, with H₂ production contributing as a considerable side reaction. Lastly, these results highlight the potential to produce Mg-doped p-type metal oxide photocathodes with a band structure tuned to optimize CO₂ reduction.