Electrodeposited BiVO4-based photoanodes for an energy-efficient photo-assisted CO2-to-formate conversion

Abstract

The development of efficient photoanodes that reduce external energy requirements for the electrochemical conversion of CO2 to formate is essential for the future implementation of this technology. In this work, we explore different photoanode structures based on electrodeposited BiVO4 onto transparent FTO substrates to achieve a more efficient PEC reduction of CO2. Among the tested structures, the photoanode incorporating a Bi2O3 underlayer, which enhances the BiVO4-FTO interface by reducing electron-hole recombination, exhibits the best PEC performance. Integrating this photoanode into a CO2 photoelectrolyzer with back visible light illumination achieves an impressive current density of −29 mA cm−2 at constant −1.8 V (vs. Ag/AgCl). Using a Bi/C GDE as the cathode, the system produces up to 56.2 g L−1 of formate with a Faradaic efficiency of 96 %. In terms of energy performance, illuminating the photoanode reduces energy consumption by nearly 40 %, bringing it down to 317 kWh kmol−1, with an energy efficiency of 38 %. The external bias can be further decreased by increasing the irradiation intensity to 2.5 suns using concentrated solar light, resulting in an additional 10 % reduction in energy consumption (290 kWh kmol−1), while maintaining high conversion efficiencies for CO2 to formate (over 95 % Faradaic efficiency). Besides, energy efficiency improves by 12 %, as the cathodic potential is reduced to −1.65 V (vs. Ag/AgCl). These results represent significant progress in reducing the external bias required for CO2 to formate conversion in PEC systems, marking a step toward the industrial application of CO2 conversion technology.