Retreat in Order to Advance: Dual-Electrode Refinery of 5-Hydroxymethylfurfural toward 2,5-Furandicarboxylic Acid with High Carbon Efficiency

Electro-refinery of 5-hydroxymethylfurfural (HMF) is an ecofriendly route to upgrade biomass feedstock under ambient conditions, producing high-value-added 2,5-furandicarboxylic acid (FDCA) and 2,5-bis(hydroxymethyl)furan (BHMF). However, FDCA electrosynthesis suffers from serious carbon loss due to HMF self-polymerization in the conventional alkaline electrolyte, emphasizing the protection of HMF via hydrogenation to robust BHMF for subsequent oxidation. Herein, dual-electrode HMF tandem refinery (DEHTR) integrated via cathodic protection and anodic oxidation, as the strategy of “retreat in order to advance” for FDCA electrosynthesis, was proposed. We developed a series of Cu-based cathodic/anodic catalysts by the alternating electrochemical treatments of copper foam, precisely regulating the active site amount/structure to accomplish the efficient HMF electro-hydrogenation (90.3% HMF conversion, 94.3% BHMF selectivity, and 86.3% FE) as well as BHMF electro-oxidation (99.3% FDCA yield and 95.5% FE). On this basis, DEHTR was finely constructed over an optimized Cu-based cathode/anode, which was expanded to a membrane-free flow electrolysis system, acquiring a higher FDCA yield and a carbon balance of 95.1% (vs 65.2% in direct HMF electro-oxidation) even at a large HMF concentration (100 mM). Moreover, gram-scale FDCA powder with 99.1% purity was simply separated from the DEHTR flow system. This work sheds light on the development of biomass electro-refinery with high carbon efficiency by collaboratively integrating dual-electrode procedures on cost-efficient electrocatalysts.