Photoelectrochemical oxidation of organic C1-molecules on co-catalyst-free bismuth vanadate photoanodes

Abstract

The transition to sustainable energy solutions is imperative due to the rising globalenergy demand and the environmental challenges associated with fossil fuel consumption. Photoelectrochemical (PEC) cells present a promising strategy by enabling the conversion of various compounds into valuable chemicals enabling thestorage of energy in the form of different substances. This approach utilizes natural light and operates at lower applied potentials compared to conventional electrochemical methods, making it an attractive alternative. Among potential photoanodematerials, bismuth vanadate (BiVO4) stands out due to its visible-light absorption,chemical stability, and favorable charge transport properties. Beyond its well-studiedrole in PEC water splitting, the oxidation of small organic molecules in PEC systemshas emerged as a compelling method for sustainable chemical synthesis, offering apathway to high-value products with reduced energy consumption and waste generation.This study investigates the feasibility of BiVO4-based photoanodes without the useof expensive or toxic cocatalysts for the oxidation of small organic molecules inaqueous systems, specifically methanol, formaldehyde, and formic acid. Using insitu flow nuclear magnetic resonance (NMR) spectroscopy, we provide direct evidence that co-catalyst-free BiVO4 does not oxidize any of these molecules under PECconditions up to potentials of 1.5 V vs reversible hydrogen electrode (RHE), contraryto previous reports in the literature. The aqueous nature of the electrolyte solutionis not the limiting factor, as measurements in an organic electrolyte solution yieldsimilar results. These findings highlight the critical role of mechanistic studies inPEC-processes and suggest a reassessment of BiVO4’s potential for PEC-drivenorganic transformations. By elucidating the fundamental limitations of pure BiVO4in these applications, this work contributes to the advancement in PEC technology,guiding the design of more efficient and selective photoanodes for energy and chemical production.