Coupling of CuO@NiBiO x Catalyzed Glycerol Oxidation to Carbon Dioxide Reduction Reaction for Enhanced Energy Efficiency

Glycerol electrooxidation reaction (GEOR) is a promising alternative to the oxygen evolution reaction (OER) in electrolyzers, overcoming the inherent challenges of high energy demand and low-value output of water oxidation. Here, we designed a non-noble metal-based electrocatalyst (CuO@NiBiO_x, CNBO) for selective and efficient GEOR. The CNBO catalyst demonstrated high selectivity and achieved nearly 100% GEOR Faradaic efficiency (FE), 80%-90% of which is conveyed into formic acid (FA). Bismuth incorporation modified the structure of the mixed oxide, increasing the surface concentration of Ni(III) species and enhancing the GEOR activity. In situ studies confirmed the formation of NiOOH, which is identified as the active site for GEOR and suggests an indirect GEOR mechanism. This study demonstrates the potential of GEOR to replace OER in Carbon dioxide reduction reaction (CO₂RR) electrolyzers. Depending on the selected CO₂RR catalyst (Ag or Sn), we could obtain either an easy-to-separate mixture of high-added value products (CO and FA) or a single product (FA) with FE_FA > 85% at both electrodes. Moreover, we demonstrate that replacing OER with GEOR in a CO₂RR-electrolyzer can save up to 25% of the electrolysis energy input, while the co-production of FA at both electrodes halves the energy per mole required for its electrosynthesis.