Sustainable carbon-based catalysts for oxygen reduction-enhanced FDCA production at ultra-low cell voltage.

The electrochemical oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) offers a sustainable pathway for bio-based polyester production. While extensive studies have focused on electrocatalyst development for this reaction, the integration of the oxygen reduction reaction (ORR) with HMF oxidation (HMFOR) remains largely underexplored. This study presents a novel electrochemical system that synergistically combines ORR with HMFOR, utilizing a tea leaf-derived carbon cathode and a nickel foam anode. The carbonization temperature of tea leaf waste was systematically optimized to finely tune the microstructure, electronic properties, and chemical compositions of the carbon electrodes. The optimal temperature of 800 °C produced a metal-free carbon catalyst with high activity and selectivity for the 2-electron ORR to HO, enabling efficient gas diffusion electrode fabrication. In a membrane-free flow cell, coupling ORR with HMFOR significantly enhanced FDCA production, achieving an 82% yield at a cell voltage as low as 1 V, compared to 72% at 2.75 V under N. Interestingly, HO did not significantly enhance HMFOR, suggesting that O primarily lowers the reaction potential rather than directly contributing to oxidation. Notably, the tea leaf-derived carbon outperformed commercial Pt/C as a cathodic catalyst for HMFOR application, delivering a higher FDCA yield at similarly low cell voltages. Our reaction design concept demonstrates a sustainable and cost-effective approach to FDCA production by utilizing biomass-derived catalysts, reducing material costs and energy requirements while enhancing scalability and efficiency.