Proton‐Coupled Electron Transfer in Photoelectrochemical Alcohol Oxidation Enhanced by Nickel‐Based Cocatalysts.

Using biomass oxidation reactions instead of water oxidation reactions is optimal for accomplishing biomass conversion and effective hydrogen generation. Here, we report that α‐Fe2O3 photoanodes with a NiOOH cocatalyst exhibit excellent performance for photoelectrochemical oxidation of 5‐hydroxymethylfurfural (HMF) to 2,5‐furandicarboxylic acid (FDCA). The conversion efficiency for HMF reaches 98.5 %, while the selectivity for FDCA is 94.2 %. We revealed that HMF is oxidized through a spontaneous proton‐coupled electron transfer (PCET) process with the high‐valent phase of the Ni‐based catalyst. The dangling oxygen and bridging oxygen of the high‐valent phase species serve as proton‐accepting sites. Furthermore, we pointed out that the deprotonated bond dissociation free energy difference between the catalysts and alcohols is the thermodynamic trigger for the PCET process. This study provides a reasonable explanation for the alcohol oxidation reaction, which is beneficial for designing biomass conversion systems. [ABSTRACT FROM AUTHOR]