P doped Ni3S2 and Ni heterojunction bifunctional catalysts for electrocatalytic 5-hydroxymethylfurfural oxidation coupled hydrogen evolution reaction

The biomass electrochemical oxidation coupled with hydrogen evolution reaction has received widespread attention due to its carbon-neutral and sustainable properties. The electrosynthesis of 2,5-furanodicarboxylic acid (FDCA) from 5-hydroxymethylfurfural (HMF) oxidation is one of the most promising means for the production of bioplastic monomers. In this work, we constructed a novel P-doped Ni₃S₂ and Ni heterojunction on nickel foam (P-Ni₃S₂/Ni/NF) using electrodeposition methods and thermal sulfuration techniques as a bifunctional catalyst for the simultaneous anodic oxidation of HMF to FDCA (HMFOR) and the cathodic hydrogen evolution reaction (HER). On one hand, the synergistic promotion of P doping and the heterojunction of Ni₃S₂ and Ni accelerated electron transfer, and on the other hand, the structure of three-dimensional microsphere stacking on NF surface to form macropores enhances the exposure of catalytically active sites. The prepared P-Ni₃S₂/Ni/NF exhibited remarkable performance with high HMF conversion (99.2 %), FDCA yield (98.1 %), and Faraday efficiency (98.8 %), and excellent stability with good product selectivity for 7 consecutive cycles, which stands at a higher level than majority of previously published electrocatalysts. Furthermore, P-Ni₃S₂/Ni/NF also shows a significant response in HER. By using HMFOR and HER as the anodic reaction and cathodic reaction, respectively, the biomass upgrading and hydrogen production can be carried out simultaneously. The synthesized P-Ni₃S₂/Ni/NF only need a voltage of 1.31 V to achieve a current density of 10 mA/cm² in a two-electrode system of HMFOR and HER, which is much lower than that of 1.48 V in OER and HER process, thus potentially reducing the cost of this process.