Surface Engineering for Efficient and Stable Photoelectrochemical Biomass Upcycling

Abstract

As the global pursuit of carbon neutrality, photoelectrochemical conversion of biomass sources as a promising strategy to produce green hydrogen while simultaneously generating value-added chemicals. This dissertation presents a comprehensive study on the design and surface engineering of photoanodes tailored for efficient and selective PEC oxidation of biomass sources, including glycerol and kraft lignin. In the first part, Fe-doped ZnS/ZnO nanowire heterostructures were developed to enhance PEC glycerol oxidation. Through synergistic effects of Fe doping and core–shell heterojunction formation, the photoanodes exhibited significantly improved charge separation, light absorption, and catalytic activity. Detailed mechanistic insights from density functional theory calculations revealed that Fe incorporation promotes favorable glycerol adsorption and enables production of value-added products with high Faradaic efficiency. The second part explores the engineering of oxygen vacancies in WO3 nanostructures to modulate surface acidity and enhance reaction selectivity. By tuning surface vacancy concentrations through thermal and chemical treatments, the optimized WO3 photoanodes achieved a high glyceraldehyde production rate (378.8 mmol·m-2·h-1) with over 86% selectivity sustained for 18 hours. A photo-induced self-healing strategy was developed to regenerate surface-active sites, thereby maintaining long-term operational stability. In the third part, a novel PEC system integrating NiCo-phthalocyanine catalysts with organic semiconductors was employed for the direct oxidation of kraft lignin. The metal-phthalocyanine catalyst enhanced catalytic activity and selectivity toward aromatic monomers such as vanillin, vanillic acid, and guaiacol. The integrated photoelectrode achieved a record-high photocurrent density (13.4 mA·cm-2) and stability over 10 hours. Density functional theory calculations confirmed the role of the metal-phthalocyanine in facilitating β-O-4 bond cleavage and suppressing electrode fouling. We believe that these findings provide a foundation for advancing photoelectrochemical biomass valorization and sustainable hydrogen production. Through the integration of nanostructure design, defect engineering, and catalytic interface optimization, this work contributes to the development of efficient, selective, and durable photoelectrochemical systems capable of converting complex biomass into value-added products.