An electrocatalytic strategy for biomass upgrading: highly selective conversion of glycerol to formic acid via NiMoO4@CuO/CF catalysis

Abstract

The electrochemical oxidation of low-cost glycerol to value-added chemicals such as formic acid is expected to meet the future energy demand as formic acid can be used as a direct or indirect fuel for formic acid fuel cells. In this work, we prepared Ni–Mo–Cu oxide catalysts by a simple hydrothermal treatment followed by calcination, yielding self-supported monolithic electrodes with markedly improved electrocatalytic properties. The optimized material comprises CuO nanowire arrays grown in situ on copper foam and coated with NiMoO₄ nanosheets (NiMoO₄@CuO/CF), and it was evaluated for application in the glycerol electrooxidation reaction (GOR). The optimized NiMoO₄@CuO/CF electrode requires a low overpotential of 1.295 V (vs. RHE) to achieve a current density of 10 mA cm⁻² and complete glycerol conversion (∼100%), along with a formic acid (FA) selectivity of 84.3% and high formic acid faradaic efficiency of 90.3%. The improved electrocatalytic performance was studied through various characterization techniques, including in situ Raman spectroscopy, operando impedance spectroscopy, open circuit potential measurements, and activation energy analysis. The experimental results indicate that the synergistic effect of CuO and NiMoO₄ is key to improving catalyst performance. CuO has a better ability to adsorb and activate glycerol, and the adsorbed glycerol can be rapidly oxidized by NiOOH active species generated in situ by electrochemical processes, promoting the cleavage of C–C bonds to obtain FA. In addition, the advanced hierarchical three-dimensional heterostructure combined with the conductive and porous NiMoO₄@CuO/CF skeleton ensures extensive exposure of active sites and rapid charge/mass transfer. These findings create an opportunity to explore Earth-abundant, non-precious electrocatalysts for the selective and efficient oxidation of glycerol into formic acid or other value-added products.