Collaborative Electrochemical Oxidation of the Alcohol and Aldehyde Groups of 5‑Hydroxymethylfurfural by NiOOH and Cu(OH)₂ for Superior 2,5-Furandicarboxylic Acid Production

Electrochemical alcohol oxidation is considered a promising alternative to the oxygen evolution reaction due to the production of high-value products and early onset potential. Herein, we analyze the different reactivities of NiOOH and Cu­(OH)₂ toward the electrochemical oxidation of alcohol and aldehyde on the furan ring and utilize their characteristics synergistically to enhance the performance of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) conversion. We discovered that Cu­(OH)₂ has higher reactivity for the oxidation of aldehyde to carboxylic acid than NiOOH, while NiOOH exhibited excellent reactivity toward the oxidation of alcohol to aldehyde. Furthermore, NiOOH–Cu­(OH)₂ mixed electrodes showed higher activity and faster conversion of HMF to FDCA than individual NiOOH or Cu­(OH)₂ electrodes. The alcohol oxidation of HMF is initiated by NiOOH, and Cu­(OH)₂ quickly converts the remaining aldehydes to carboxylic acids at the NiOOH/Cu­(OH)₂ interface. Further enhancement of the HMF oxidation kinetics of NiOOH/Cu­(OH)₂ was achieved by preparing a nanofoam structure comprising nanoscale pores and nanodendritic frames, showing instantaneous conversion to FDCA without producing unreacted intermediates.