Photoelectrochemical‐Unassisted Glycerol Oxidation Coupled with CO 2 Reduction to Value‐Added Chemicals

Abstract Photoelectrodes based on earth‐abundant elements, FTO|BiVO 4 and Ni foam |Cu 2 O/CuO/TiO 2 , were assembled in a parallel‐configured flow photoelectrochemical (PEC) electrolyser and provided unassisted conversion of glycerol and CO 2 into value‐added chemicals under solar‐simulated irradiation. The photoelectrodes PEC properties were firstly evaluated in aqueous NaHCO 3 electrolyte, using platinum as auxiliary electrode, for determination of wavelength‐resolved light harvesting, flat band potential, conduction and valence band edges, charge‐separation and injection efficiencies. Comparison of Ni foam |Cu 2 O, Ni foam |Cu 2 O/CuO and Ni foam |Cu 2 O/CuO/TiO 2 for PEC CO 2 reduction revealed that Cu 2 O/CuO improved light harvesting and selectivity for ethanol production, while TiO 2 protected the photocathode against photodegradation. Under illumination, the PEC flow electrolyser assembled with FTO|BiVO 4 and Ni foam |Cu 2 O/CuO/TiO 2 exhibited + 0.56 V of open‐circuit photovoltage and a spontaneous short‐circuit photocurrent (1.7 to 1 mA in 2 h), attributed to the suitable alignment of the band edges of these photoelectrodes. After 2 h PEC electrolysis, formate (229 µg cm −2 h −1 ) and glycolate (58.5 µg cm −2 h −1 ) were produced in the anodic compartment with faradaic efficiencies of 69% and 13%, respectively. The cathodic compartment generated 26 µg cm −2 h −1 of ethanol (FE = 32%). This flow PEC electrolyser demonstrates a proof‐of‐concept for a practical solar‐to‐chemicals production using industrial by‐products as feedstocks.