Solar-driven photoelectrochemical conversion of biomass: recent progress, mechanistic insights and potential scalability

Abstract

The selective conversion of renewable biomass to value-added chemicals/fuels via environment-friendly photoelectrochemical (PEC) technology has enormous development potential for solving the increasingly serious problems associated with the energy crisis and environmental pollution. However, PEC biomass conversion is a complex process involving photogenerated carrier separation, multiple-electron/proton transfer and different bonds evolution. Presently, the main challenge is improving the catalytic activity of semiconductor photoelectrodes and the selectivity for target products while co-producing high-value by-products (e.g., H₂). In this review, we elaborate on the fundamental principles of PEC cells and the strategies for promoting the bandgap and structure regulation of photoelectrodes such as doping, defect engineering, facet engineering, cocatalyst loading and heterojunction formation. On this basis, we discuss the PEC mechanisms of upgrading biomass-derived compounds, including aliphatic alcohols (methanol, ethanol, and glycerol), aromatic alcohols (benzyl alcohol), aldehydes (glyoxal and glucose), furans (5-hydroxymethylfurfural and furfural) and hydrocarbons (methane, cyclohexane and benzene). Moreover, we describe the introduction of redox couples (nitroxyl radicals, polyoxometalate, chloride, and bromide) and redox enzymes acting as proton/charge transfer mediators in PEC cells to boost biomass conversion. Subsequently, we systematically summarize the recent progress in the development of dual-function PEC cells with anodic biomass oxidation and the cathodic HER/ORR/CO₂RR/NiRR for enhanced hydrogen production, electricity generation and preparation of value-added chemicals/fuels. Finally, we present the main challenges and perspectives for the future exploration, innovation, and, ultimately, commercialization of PEC biomass conversion.