Performance study on electrocatalytic oxidation of 5-hydroxymethylfurfural by Nickel-Cobalt-Manganese sulfide

As countries’ demand for fossil fuels and resources continues to increase, it is particularly critical to reduce dependence on these energy sources and actively promote new green renewable resources. 5-Hydroxymethylfurfural (HMF) has been identified as one of the important biomass platform chemicals, which can be converted into a series of valuable chemicals through reaction. Its typical oxidation product, 2,5-furanediformic acid (FDCA), can replace petroleum-based terephthalic acid (TPA), and also has important applications in metal-organic framework materials, chemical synthesis, etc. This is essential for mitigating the global fossil resource crisis and achieving carbon peaking and carbon neutrality goals. However, traditional HMF thermochemical oxidation typically requires reactions under harsh conditions to achieve high HMF conversion and FDCA yield. In comparison, the electrocatalytic oxidation of 5-hydroxymethylfurfural (HMFOR) is a clean and environmentally friendly method with mild reaction conditions, simple operation, and high energy efficiency. Its theoretical oxidation potential is 0.3 V, which is lower than the kinetic slow OER (1.23 V). It can replace OER in anodic reactions and generate H₂ and high value-added chemicals at the same time, improving energy efficiency. Therefore, it is of great significance to design electrocatalysts with high catalytic activity, high energy utilization and low cost. Transition metal sulfides have attracted much attention due to their abundant raw material storage, simple preparation methods, and high electrical conductivity. Previous studies have shown that transition metal sulfides form layered structures under the influence of van der Waals forces, which can expose more activity check points and increase the specific surface area of activity to participate in the reaction, thereby improving the electrocatalytic performance. Studies have shown that multi-component metal sulfides tend to exhibit higher HMFOR activity than single metal sulfides, due to the synergistic effect of multiple metal ions and the promotion of multiple oxidation-reduction reactions by multiple valence states. Compared with the adhesive required for powder catalysts, the catalyst can be directly grown on conductive substrates such as nickel foam (NF), carbon cloth (CC), and copper foam (CF) with high specific surface area, so that the catalyst can be exposed to more active sites and is more stable. Based on this, NiCoMn_x/NF precursors with different Ni/Co ratios were prepared by hydrothermal method using three-dimensional nickel foam as the substrate, and then they were hydrothermally vulcanized to obtain NiCoMn_x-S_y/NF sulfides at different concentrations. The catalysts were tested by linear scanning voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and open circuit potential test (OCPT). The catalysts were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and specific surface area analysis (BET). The results of electrochemical analysis show that NiCoMn₄/NF has relatively better HMFOR performance, and NiCoMn₄/NF with better comprehensive performance is selected for the next vulcanization process. NiCoMn₄-S_0.10/NF with vulcanization concentration of 10 mmol/L has excellent HMFOR performance, and HMFOR reaction is carried out at 300 r/min rotational speed and 1.37 V voltage. The conversion rate of HMF, the yield of FDCA and FE can reach 99.41%, 98.84% and 97.31%, respectively. And after 10 consecutive HMF electrolytic oxidation experiments, the catalytic efficiency did not decrease significantly, indicating that NiCoMn₄-S_0.10/NF has good cycle durability. The results of catalyst characterization showed that the conductivity and specific surface area of the catalyst increased greatly after vulcanization. The surface reconfiguration of the sulfide on the catalyst surface to (Ni, Co)OOH occurs, and (Ni, Co)OOH is the true active site of HMFOR. At the same time, Mn doping can add a new adsorption site for HMF oxidation, and promote the adsorption of HMF molecules on the surface of NiCoMn₄-S_0.10/NF, which makes NiCoMn₄-S_0.10/NF have excellent HMFOR performance.