Abstract: Photoelectrochemical (PEC) systems offer a promising solar-driven approach to address the high energy demand of the oxygen evolution reaction (OER), which often limits conventional electrochemical reduction of CO2 to value-added products. In this context, replacing the anodic OER with the glycerol oxidation reaction (GOR) has emerged as an effective strategy to enhance the full energy efficiency (FEE) of PEC CO2 conversion systems, while enabling the simultaneous valorisation of biomass-derived feedstocks. In this work, advanced multilayered BiVO4/WO3/CaTiO3 (CWB) photoanodes decorated with Ni, Co, and Ni-Co nanoparticles are fabricated and applied to promote energy-efficient CO2 reduction to formate (HCOO-) coupled with glycerol photoelectrooxidation. The results show that the Ni-decorated photoanode (CWBNi) achieves a maximum HCOO- production rate of 2200 µmol m-2 s-1, with a cathodic Faradaic efficiency of 94.3%. Simultaneously, the GOR yields dihydroxyacetone (DHA), at a production rate of 184.8 µmol m-2 s-1, along with glyceraldehyde (GLAD) and acetate (CH3COO-) as the major oxidation products, at a current density of 45 mA cm-2 under visible light illumination (1 sun). Overall, a maximum FEE of 60% is achieved with the CWBNi photoanode, outperforming both the Ni/Co (50:50) and Co-based counterparts. These findings highlight the critical role of photoanode composition and architecture to enhance both FEE and operational stability in the simultaneous co-production of value-added chemicals.

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