Photoelectrochemical Upgrading of Biomass-Derived Compounds over Hematite Nanorods Decorated with Bimetallic Zeolitic Imidazolate Frameworks
Replacing the kinetically sluggish oxygen evolution reaction (OER) with biomass oxidation at photoanodes offers a cost-effective and energy-efficient route for simultaneous hydrogen production and value-added chemical synthesis in a photoelectrochemical (PEC) cell. Here, titanium-doped hematite nanorods (Hem) decorated with CoNi bimetallic zeolitic imidazolate frameworks (ZIF) were prepared via room-temperature deposition and employed as photoanodes for 5-hydroxymethylfurfural (HMF) oxidation. Using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) as a redox mediator in alkaline electrolyte, the CoNi-ZIF/Hem photoanode achieved a photocurrent density of 1.09 mA cm−2 at a low bias of 1.1 V vs. reversible hydrogen electrode (RHE). Experimental results and theoretical calculations reveal that CoNi-ZIF accelerates charge transfer and separation, and enhances TEMPO adsorption on the surface, benefiting PEC TEMPO-mediated HMF oxidation to 2,5-furandicarboxylic acid (FDCA). In a flow-cell reactor under 1 sun illumination, the photoanode achieved ~99% HMF conversion and ~98% FDCA yield within 2 hours. The photoanode also exhibited excellent performance for TEMPO-mediated oxidation of various aldehyde-containing biomass-derived compounds. This work demonstrates a rational design of hematite-based photoanodes for efficient biomass valorization coupled with hydrogen production.