Fabrication and optimization of perovskite-based photoanodes for solar-driven CO2 photoelectroreduction to formate

The photoelectrochemical reduction of CO2 to value-added products represents a promising strategy for mitigating CO2 emissions. However, further research efforts need to be undertaken to enable the technology for scaleup, including the design and fabrication of efficient photoelectrodes capable of yielding substantial photogenerated current densities. In this work, a photoanode combining a commercial calcium titanate perovskite (CaTiO3) and BiVO4 layers coated onto a transparent FTO substrate by automated spray pyrolysis is proposed. Different photoanode configurations are tested, with the most favourable results achieved when BiVO4 is positioned as the top layer with back illumination. The optimization of the catalytic loading is also assessed, finding an optimal at 1 mg cm -2 of CaTiO3 and 3 mg cm -2 of BiVO4, resulting in an impressive current density of -71 mA cm -2 at -1.8 V vs. Ag/AgCl. This optimal photoanode is then integrated into an electrolyzer for continuous visible light-driven CO2 reduction in the gas phase to formate, obtaining a concentration of 63.8 g L-1, with a Faradaic Efficiency of 79.1 %, and solar-to-fuel conversion efficiency of 7.6 %. These results represent a significant advancement in the development of photoanodes, offering promise for the future scalability of photoelectrochemical CO2 reduction processes.