Transition Metal Sulfides Supported on Sulfonated CNT-Chitosan Derived Carbon Aerogel for Efficient Electrooxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

In this study, we present a straightforward synthesis strategy to prepare transition metal sulfide electrocatalysts supported on sulfonated carbon nanotube-chitosan-derived carbon aerogel. Highly dispersed Ni 3 S 2 @CNT, Cu 7 S 4 @CNT, and Co 4 S 3 @CNT were successfully fabricated and applied for 5-hydroxymethylfurfural (HMF) electrooxidation to 2,5-furandicarboxylic acid (FDCA). Among them, Co 4 S 3 @CNT exhibited remarkable electrocatalytic activity, delivering a current density of 100 mA cm –2 at a low potential of 1.367 V (vs RHE) while attaining 99.82% HMF conversion, 99.97% FDCA selectivity and a Faradaic efficiency of 83.75%. Electrochemical measurements revealed that Co 4 S 3 @CNT possesses an electrochemical active surface area (ECSA) of 0.781 μF cm –2 , which is higher than those of Ni 3 S 2 @CNT and Cu 7 S 4 @CNT, implying an increased population of active sites and enhanced catalytic activity. In-situ Raman spectroscopy reveals that Co 4 S 3 @CNT undergoes a progressive reconstruction from Co(OH) 2 to CoOOH under anodic conditions, with CoOOH formation being significantly delayed in the presence of HMF, confirming its role as the active phase. Density functional theory (DFT) calculations further indicate that the excellent performance of Co 4 S 3 @CNT originates from the lowest energy barrier (1.84 eV) for the rate-determining catalyst activation dehydrogenation step, coupled with its pronounced charge-polarization capability that facilitates HMF preactivation. This work gives a promising design approach for developing efficient nonprecious metal electrochemical catalysts toward biomass valorization.