Stabilities, Regeneration Pathways, and ElectrocatalyticProperties of Nitroxyl Radicals for the Electrochemical Oxidationof 5‑Hydroxymethylfurfural

2,5-Furandicarboxylic acid (FDCA) is a near-market monomer that has been identified as a viable biomass-derived replacement for petroleum-derived terephthalic acid in the synthesis of polyethylene terephthalate (PET). FDCA can be produced from the oxidation of 5-hydroxymethylfurfural (HMF), which is a versatile biomass intermediate produced from the dehydration of C-6 monosaccharides obtained from cellulosic biomass. In this study, we comparatively investigated the use of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-acetamido-TEMPO (ACT) for electrochemical HMF oxidation to FDCA. The distinct advantage of TEMPO- and ACT-mediated electrochemical oxidation of HMF is that they can efficiently achieve HMF oxidation in mildly basic conditions (pH 9–10), while other heterogeneous catalysts typically require the use of more basic media. Since HMF oxidation in a strongly basic condition increases the chance to form humins, which are difficult to separate from FDCA and decrease the commercial viability of FD...