Solar-Driven Biomass Conversion of HMF Via TEMPO Mediation

Processing of biomass into high-value chemicals or fuel is an energy intensive process due to the energetically unfavorable thermodynamics governing the conversion reactions. This high energy requirement hinders the ability of bio-fuels to replace more commonly used, nonrenewable fuel sources. However, with the use of photoelectrochemical cells (PECs), sunlight can be harnessed to power biomass conversion to valuable products. In this study, solar-driven oxidation of 5-hydroxymethylfurfural (HMF) to 2,5 furandicarboxylic acid (FDCA) was investigated by applying a bismuth vanadate semiconductor to a custom-built PEC. The reaction was mediated through the use of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) at ambient pressure and temperature. HMF is a biomass intermediate derived from glucose while FDCA is one of twelve chemicals identified by the US Department of Energy as being a vital platform chemical obtainable through lignocellulosic biomass. In this study, TEMPO-mediated photoelectrochemical oxidation of HMF was acheived with nearly 80% conversion. Water oxidation was not observed, suggesting that water oxidation is thermodynamically less favorable than TEMPO-mediated HMF oxidation. The work here demonstrates the viability of solar powered oxidation of HMF mediated through TEMPO and opens doors into the advantages that PEC use can provide.