NiSX/carbon black hybrids for efficient electrochemical oxidation of 5-hydroxymethyfurfural to 2,5-furandicarboxylic acid

Abstract

NiS_X stands out in the electrochemical oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) due to the favorable conductivity and diverse chemical composition. However, NiS_X usually exhibits few exposed active sites and poor charge transfer kinetics. Moreover, during the electrochemical oxidation of HMF, the conductivity of the catalyst would decrease rapidly with the formation of oxidized Ni species, leading to a rapid decline in catalytic performance. Therefore, a series of NiS_X/carbon black (CB) hybrids (NiS_X/CB-n) were synthesized via a one-step solvent hydrothermal method in which NiS_X displayed a large cubic block structure assembled from small nanosheets. Among the prepared catalysts, NiS_X/CB-2, with the optimal amount of introduced CB, exhibited superior electrocatalytic activity for the oxidation of HMF, achieving 100% HMF conversion, 98% FDCA yield, and 100% Faradaic efficiency at 1.45 V (vs. RHE). The outstanding electrocatalytic activity of NiS_X/CB-2 was attributed to the suitable CB doping, which not only enhanced the conductivity of catalyst but also separated the small nanosheets, preventing the formation of densely packed NiS_X structure and increasing the specific surface area of catalyst, thereby exposing more active sites and improving the availability of material. Furthermore, the formation of C-S bonds facilitated charge interactions between NiS_X and CB, promoting the transfer of charges during the electrolysis process and enhancing electrocatalytic kinetics. Open circuit potential tests demonstrated that the introduction of CB also strengthened the adsorption capacity of catalyst for HMF, further benefiting its electrocatalytic activity.