Unassisted Photoelectrochemical CO₂ Conversion into Liquid Products by a Light-Responsive Gas-Diffusion Electrode

The combination of suitable semiconductors as photoelectrodes could sustainably provide unassisted CO₂ conversion using sunlight; however, few reports describe such achievement at this time. Herein, ethanol and formate were produced in a photoreactor assembled with a photoresponsive gas-diffusion electrode (GDE) containing Cu₂WO₄. The energy diagram, built from band gap energy and flat band potential (<i>E</i>_FB) values, shows that the position of the Cu₂WO₄ conduction band edge is suitable to promote CO₂ reduction in different products. BiVO₄ deposited on titanium foil was used as the photoanode; large-area Ti|BiVO₄ was successfully synthesized from the Ti|BiOI template; additional deposition of FeOOH/NiOOH decreased EFB and charge recombination, improving the photoanode performance for the O₂ evolution reaction. The CO₂-fed GDE/Cu₂WO₄ (7.5 cm²) photocathode and the Ti|BiVO₄/FeOOH/NiOOH (9.0 cm²) photoanode were assembled in a H-type reactor containing NaHCO3 aqueous solution. Under irradiation, these associated photoelectrodes supplied the thermodynamic requirements for a spontaneous current flow of 0.7 mA and, without any external bias, produced formate (16.5 μg h^–1 cm^–2) and ethanol (1.9 μg h^–1 cm^–2) at the cathode with solar-to-fuel efficiency of 0.07 and 0.005%, respectively. This photoreactor can be an inspiration for designing sustainable devices for CO₂ valorization using sunlight.<br/><br/>