Electrocatalytic Oxidation of Glycerol to Formic Acid by CuCo₂O₄Spinel Oxide Nanostructure Catalysts

The electrochemical oxidation of abundantly available glycerol for the production of value-added chemicals, such as formic acid, could be a promising approach to utilize glycerol more effectively and to meet the future demand for formic acid as a fuel for direct or indirect formic acid fuel cells. Here we report a comparative study of a series of earth-abundant cobalt-based spinel oxide (MCo2O4, M = Mn, Fe, Co, Ni, Cu, and Zn) nanostructures as robust electrocatalysts for the glycerol oxidation to selectively produce formic acid. Their intrinsic catalytic activities in alkaline solution follow the sequence of CuCo2O4 > NiCo2O4 > CoCo2O4 > FeCo2O4 > ZnCo2O4 > MnCo2O4. Using the best-performing CuCo2O4 catalyst directly integrated onto carbon fiber paper electrodes for the bulk electrolysis reaction of glycerol oxidation (pH = 13) at the constant potential of 1.30 V vs reversible hydrogen electrode (RHE), a high selectivity of 80.6% for formic acid production and an overall Faradaic efficiency of 89.1% toward all value-added products were achieved with a high glycerol conversion of 79.7%. Various structural characterization techniques confirm the stability of the CuCo2O4 catalyst after electrochemical testing. These results open up opportunities for studying earth-abundant electrocatalysts for efficient and selective oxidation of glycerol to produce formic acid or other value-added chemicals.