Reaction kinetics of photoelectrochemical water and 5-hydroxymethylfurfural oxidation on rutile nanorod photoanode with Ge doping and core/ shell structure

A high-performance TiO2/Ge-TiO2 nanorod photoanode, with the synergistic effect of Ge doping and core/shell structuring on promoting charge separation, was used in the photoelectrochemical H-2 production system. The TiO2/Ge-TiO2 photoanode exhibited >90% hole transfer efficiency at 1.23 V vs. RHE for water oxidation. Moreover, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated hydroxymethylfurfural (HMF) oxidation was achieved on the TiO2 photoanodes for the first time. Notably, the kinetics of HMF oxidation were slower compared to water oxidation, resulting in a higher Faraday efficiency (FEHMF) corresponding to a lower hole transfer efficiency. The oxidation of HMF on the TiO2 photoanodes was found to predominantly follow the pathway dominated by 2,5-diformylfuran (DFF). The FEHMF displayed variation on the TiO2 photoanodes, with Ge doping leading to a decrease by enhancing surface hydrophilia. However, this decrease was effectively compensated for by the overlay of the TiO2 shell. Consequently, the TiO2/Ge-TiO2 photoanode achieved the highest HMF conversion rate, which can be attributed to the accelerated production and conversion of DFF. This work expands the application of TiO2 photoanodes on biomass conversion and sheds light on the pathway and kinetic characteristics of TEMPO-mediated HMF oxidation processes.