One-step in-situ synthesis of nickel–cobalt sulfide catalysts for ultra-efficient electrooxidation of 5-hydroxymethylfurfural

This study presents Ni₇Co₃-S achieving 99.2 % HMF conversion, 96.1 % FDCA yield, and 98.5 % Faradaic efficiency at 1.45 V, with FDCA rates at 266.7 µmol cm^-2h⁻¹ in a 30 mL, 20 mM HMF electrolyte. At the same operational potential, this catalyst achieved a current density of 105 mA cm⁻² in 1 M KOH with 20 mM HMF, outperforming 26mA cm⁻² of Ni₇Co₃-O. Linear sweep voltammetry (LSV) analysis reveals that Ni₇Co₃-S has an onset potential of 1.16 V, which is 90 mV lower than Ni₇Co₃-O. With a Tafel slope of 89.1 mV dec^-1, versus 110.3 mV dec^-1 for Ni₇Co₃-O, Ni₇Co₃-S exhibits quicker reaction kinetics. Additionally, Ni₇Co₃-S boasts double-layer capacitance twice that of Ni₇Co₃-O, while sulfidation decreases in Ni²⁺ and Co³⁺ alongside an increase in Ni³⁺ and Co²⁺, suggesting enhanced electron transfer from Ni to Co. These insights offer a strategy for developing high-performance, non-precious catalysts for HMF electrooxidation.