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

• Different BiVO 4 -based photoanodes with alternative structures are electrodeposited. • The photoanode with improved FTO-BiVO 4 interface presents the best PEC performance. • 56 g L −1 and FE of 96 % to formate can be reached with the best-performance photoanode. • The energy consumption improves under illumination, reducing EC by 40% • A solar concentration of 2.5 suns enhances the EE to formate by 12 % The development of efficient photoanodes that reduce external energy requirements for the electrochemical conversion of CO 2 to formate is essential for the future implementation of this technology. In this work, we explore different photoanode structures based on electrodeposited BiVO 4 onto transparent FTO substrates to achieve a more efficient PEC reduction of CO 2 . Among the tested structures, the photoanode incorporating a Bi 2 O 3 underlayer, which enhances the BiVO 4 -FTO interface by reducing electron-hole recombination, exhibits the best PEC performance. Integrating this photoanode into a CO 2 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 CO 2 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 CO 2 to formate conversion in PEC systems, marking a step toward the industrial application of CO 2 conversion technology.