HMF electrooxidation on robust nickel-foam catalysts: effect of pH on electrolysis performance

Among biomass-derived compounds, 5-hydroxymethyl furfural (HMF) has substantial potential as a key platform chemical for producing value-added compounds. The electrochemical oxidation of HMF to 2,5-furandicarboxylic acid (FDCA), a crucial precursor for bio-based polyethylene furanoate plastics, has garnered particular attention as a green and efficient alternative to the conventional anode reactions of power-to-value electrolyser systems. On NiOOH-based electrocatalysts, studied in this paper, the electrochemical HMF oxidation reaction (HMFOR) already becomes at least partially transport-controlled, so that the availability of reactants (both OH – and HMF) at the electrode surface will have a crucial role in determining electrolysis performance. Voltammetric and potentiostatic analyses demonstrate a strong influence of the solution pH on both the reaction rate and the product selectivity, with higher alkalinity favoring selective oxidation to FDCA. On the other hand, extreme high alkalinity accelerates HMF degradation to undesirable byproducts, and complicates the isolation of FDCA. We found that the OH – concentration of the anolyte should outrange that of HMF 2 to 4 times in order to maximize the FDCA production rate. Furthermore, our results underscore the importance of maintaining sufficient OH − ion availability during prolonged electrolysis to ensure efficient catalyst performance and system stability. These findings provide valuable insights into optimizing HMFOR systems, and may lead to sustainable and economically viable production of FDCA and other bio-derived chemicals.