Solar-driven upgrading of 5-hydroxymethylfurfural on BiVO4 photoanodes: Effect of TEMPO mediator and cocatalyst on reaction kinetics

Biomass upgrading driven by solar energy in a photoelectrochemical (PEC) cell offers an energy-saving and cost-effective alternative route to yield value-added products. Herein, we report remarkably efficient solar-driven TEMPO mediated 5-hydroxymethylfurfural (HMF) oxidation over NiFe-LDH/BiVO4 photoanodes: yield of 2,5-furandicarboxylic acid (FDCA) and faradaic efficiency increase from 1.7 %/2.5 % over BiVO4 to ∼100 %/100 % over 1-LDH/BiVO4 at 0.7 VRHE, demonstrating boosted catalytic efficiency and utility of PEC cells. The distinctly larger surface potential difference (1.5 times) validates the effective charge separation and transfer in 1-LDH/BiVO4, and more holes can be available to oxidize TEMPO. The effect of TEMPO is carefully investigated and it suggests that TEMPO-mediated PEC oxidation of HMF is thermodynamically and kinetically favorable in contrast to water oxidation. Superb reactivity can be achieved with an increase of TEMPO concentration. This work demonstrates that solar-driven biomass upgrading can be a feasible anode reaction for solar-fuel production by replacing the sluggish water oxidation process.