Electrochemical Oxidation of 5-Hydroxymethylfurfural on Nickel Nitride/Carbon Nanosheets: Reaction Pathway Determined by In Situ Sum Frequency Generation Vibrational Spectroscopy

2,5-Furandicarboxylic acid was obtained from the electrooxidation of 5-hydroxymethylfurfural (HMF) with non-noble metal-based catalysts. Moreover, combining the biomass oxidation with the hydrogen evolution reaction (HER) increased the energy conversion efficiency of an electrolyzer and also generated value-added products at both electrodes. Here, the reaction pathway on the surface of a carbon-coupled nickel nitride nanosheet (Ni3N@C) electrode was evaluated by surface-selective vibrational spectroscopy using sum frequency generation (SFG) during the electrochemical oxidation. The Ni3N@C electrode shows catalytic activities for HMF oxidation and the HER. As the first in situ SFG study on transition-metal nitride for the electrooxidation upgrade of HMF, this work not only demonstrates that the reaction pathway of electrochemical oxidation but also provides an opportunity for nonprecious metal nitrides to simultaneously upgrade biomass and produce H-2 under ambient conditions.