Synthesis of carbonate-intercalated copper–cobalt layered double hydroxide for efficient electrochemical conversion of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid

Abstract

Carbonate-intercalated copper–cobalt layered double hydroxide (CuCo–CO₃/LDH) was synthesized using a hydrothermal method. The synthesized catalyst was employed for the electrochemical conversion of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). The reaction was conducted in an H-type electrochemical cell separated by a Nafion membrane to ensure efficient product separation. The CuCo–CO₃/LDH catalyst demonstrated a significantly lower overpotential (1.34 V vs. RHE), for HMF oxidation compared to the oxygen evolution reaction (OER) (1.59 V vs. RHE), along with a higher current density in alkaline media. Electrochemical impedance spectroscopy (EIS) revealed a reduced charge transfer resistance of 0.82 Ω during the HMF oxidation reaction (HMFOR), further validating its enhanced electrocatalytic performance. Kinetic analysis showed that the exchange current density (j₀) for HMF oxidation was 1.25 × 10⁻³ A cm⁻², markedly higher than that of the OER (2.44 × 10⁻⁶ A cm⁻²), indicating superior reaction kinetics. The apparent rate constant (k) for the HMF oxidation pathway was calculated to be 2.23 × 10⁻² s⁻¹. The catalyst achieved a faradaic efficiency of 96.82% for HMF oxidation and an FDCA yield of 97.46%, while maintaining a high conversion efficiency (94.42%) and yield (92.2%) over three repeated cycles of use. These findings establish CuCo–CO₃/LDH as a robust, energy-efficient, and scalable electrocatalyst for green biomass valorization.