In a typical ​hydrogen-producing photoelectrochemical cell (PEC), ​water reduction at the cathode (producing ​hydrogen) is accompanied by ​water oxidation at the anode (producing ​oxygen). This anode reaction is, however, not kinetically favourable. Here we investigate the possibility of utilizing solar energy for biomass conversion by performing the oxidation of ​5-hydroxymethylfurfural (​HMF) into ​2,5-furandicarboxylic acid (​FDCA) at the anode of a PEC. ​HMF is a key intermediate in biomass conversion, and ​FDCA is an important monomer for the production of numerous polymers. Using ​2,2,6,6-tetramethylpiperidine-1-oxyl as a mediator, we obtained a near-quantitative yield and 100% Faradaic efficiency at ambient conditions without the use of precious-metal catalysts. This reaction is also thermodynamically and kinetically more favourable than ​water oxidation. Our results suggest that solar-driven biomass conversion can be a viable anode reaction that has the potential to increase both the efficiency and the utility of PECs constructed for solar-fuel production.

http://www.nature.com/nchem/journal/v7/n4/full/nchem.2194.html

Nature Chemistry 7, 328–333 (2015) doi:10.1038/nchem.2194