In situ modification of BiVO4 nanosheets on graphene for boosting photocatalytic water oxidation

Nanoarchitectonics on Z-scheme and Mott-Schottky heterostructure for photocatalytic water oxidation via dual-cascade charge-transfer pathways

The bottleneck for water splitting to generate hydrogen fuel is the sluggish oxidation of water. Even though the monoclinic-BiVO₄ (m-BiVO₄)-based heterostructure has been widely applied for water oxidation, carrier recombination on dual surfaces of the m-BiVO₄ component have not been fully resolved by a single heterojunction. Inspired by natural photosynthesis, we established an m-BiVO₄/carbon nitride (C₃N₄) Z-scheme heterostructure based on the m-BiVO₄/reduced graphene oxide (rGO) Mott-Schottky heterostructure, constructing the face-contact C₃N₄/m-BiVO₄/rGO (CNBG) ternary composite to remove excessive surface recombination during water oxidation. The rGO can accumulate photogenerated electrons from m-BiVO₄ through a high conductivity region over the heterointerface, with the electrons then prone to diffuse along a highly conductive carbon network. In an internal electric field at the heterointerface of m-BiVO₄/C₃N₄, the low-energy electrons and holes are rapidly consumed under irradiation. Therefore, spatial separation of electron-hole pairs occurs, and strong redox potentials are maintained by the Z-scheme electron transfer. These advantages endow the CNBG ternary composite with over 193% growth in O₂ yield, and a remarkable rise in ·OH and ·O₂^- radicals, compared to the m-BiVO₄/rGO binary composite. This work shows a novel perspective for rationally integrating Z-scheme and Mott-Schottky heterostructures in the water oxidation reaction.

Synergetic Nanoarchitectonics of Defects and Cocatalysts in Oxygen-Vacancy-Rich BiVO4/reduced graphene oxide Mott-Schottky Heterostructures for Photocatalytic Water Oxidation

Water oxidation process is a pivotal step of photosynthesis and stimulates the progress of high-performance catalysts for renewable fuel production. Despite the performance benefit of cocatalysts, defect engineering holds promise to settle inherent limitations of semiconductors aiming at sluggish water oxidation. Here, we modify the in situ growth pathway of monoclinic BiVO₄ (m-BiVO₄) on reduced graphene oxide (rGO), constructing abundant surface oxygen vacancies (O_V)-incorporated m-BiVO₄/rGO heterostructure toward water oxidation reaction under visible light. Owing to the O_V in the m-BiVO₄ component, a vacancy-related defect level allows more electrons to be photoexcited by low-energy photons to cause the electron transition, boosting photoabsorption as well as photoexcitation. Besides, the O_V can reinforce surface adsorption and reduce the dissociation energy of water molecules. Particularly because of the synergy of O_V and cocatalyst rGO, the O_V functions as electron-trapped sites to facilitate the carrier separation; the rGO not only receives electrons from m-BiVO₄ promoted by internal electric field over Mott-Schottky heterostructures but also spurs further electron diffusion along a highly conductive carbon network. These merits enable the O_V-incorporated m-BiVO₄/rGO heterostructure with an over 209% growth in O₂ yield relative to the counterpart. The increased performance is also validated by the significant rise of ^•OH radicals and ^•O₂^- radicals. The current work paves a novel avenue for the integration of defect engineering and cocatalyst coupling in artificial photosynthesis.

Construction of BiVO4/NiCo2O4 nanosheet Z-scheme heterojunction for highly boost solar water oxidation

The sluggish water oxidation process is a severe obstacle for solar-driven water splitting. Therefore, it is imperative to develop a suitable photocatalyst with reduced energy barrier for strong oxidation. In this study, a Z-scheme BiVO₄/NiCo₂O₄ (BVO/NCO) heterojunction system was designed by decorating ultrathin nickel-cobalt (NiCo₂O₄) spinel nanosheets on BiVO₄ as an efficient photocatalyst for water oxidation. The unique structure of the system significantly reduced the energy barrier and improved the oxidation ability of BiVO₄ to efficiently enhance the separation and transfer of the photogenerated carriers. Thus, the photocatalyst delivered an excellent O₂ evolution performance of 1640.9 μmol∙g^-1∙h^-1 and showed 124% improved efficiency as compared to pristine BiVO₄ and a quantum efficiency of 5.39% at 400 nm for O₂ evolution. Additionally, the theoretical calculations revealed that the formation of *OOH was the rate-determining step for water oxidation. The decoration with NiCo₂O₄ significantly reduced the energy barrier between *O and *OOH, which eventually improved the photocatalytic performance of BVO/NCO. The results hold great promise for the potential application of spinel-based materials in efficient photocatalytic O₂ evolution and offer fundamental insights into the design of efficient water oxidation heterojunctions.

Vacancy defect engineering of BiVO4 photoanodes for photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting has been regarded as a promising technology for sustainable hydrogen production. The development of efficient photoelectrode materials is the key to improve the solar-to-hydrogen (STH) conversion efficiency towards practical application. Bismuth vanadate (BiVO₄) is one of the most promising photoanode materials with the advantages of visible light absorption, good chemical stability, nontoxic feature, and low cost. However, the PEC performance of BiVO₄ photoanodes is limited by the relatively short hole diffusion length and poor electron transport properties. The recent rapid development of vacancy defect engineering has significantly improved the PEC performance of BiVO₄. In this review article, the fundamental properties of BiVO₄ are presented, followed by an overview of the methods for creating different kinds of vacancy defects in BiVO₄ photoanodes. Then, the roles of vacancy defects in tuning the electronic structure, promoting charge separation, and increasing surface photoreaction kinetics of BiVO₄ photoanodes are critically discussed. Finally, the major challenges and some encouraging perspectives for future research on vacancy defect engineering of BiVO₄ photoanodes are presented, providing guidelines for the design of efficient BiVO₄ photoanodes for solar fuel production.

Construction of a Bioinspired Hierarchical BiVO4/BiOCl Heterojunction and Its Enhanced Photocatalytic Activity for Phenol Degradation

Development of a p-n heterojunction to achieve efficient degradation of organic pollutants is a promising approach in the field of photocatalysis. Herein, BiVO₄ with bioinspired hierarchical structures was prepared with the sol-gel method and combined with BiOCl nanoplates to construct a 3D/2D configuration via an in situ deposition route. The hierarchical BiVO₄ served as an excellent substrate to achieve the uniform loading of BiOCl nanoplates. The obtained 3D/2D BiVO₄/BiOCl hybrids exhibited significantly enhanced photocatalytic efficiency for degrading phenol under visible light irradiation, with a first-order reaction rate constant that was 9.9 and 1.9 times higher than those of hierarchical BiVO₄ and the BiVO₄/BiOCl hybrids without hierarchical structures, respectively. Moreover, the hierarchical BiVO₄/BiOCl also displayed good photochemical stability for the degradation of phenol after three recycles. The p-n heterojunction and hierarchical structure worked together to form a spatial conductive network framework, which possessed improved visible light absorption, high specific surface area, as well as effective separation and transfer of photogenerated charge carriers.

Surface Reconstruction-Associated Partially Amorphized Bismuth Oxychloride for Boosted Photocatalytic Water Oxidation

The molecule water activation is believed to be one of the most critical steps that is closely related to the proceeding of photoinduced reaction, such as overall water splitting, carbon dioxide conversion, and organic contaminant degradation. As metal oxides possessing a regular structure with high crystallinity are widely accepted as promising for effective catalysis, numerous studies have been devoted to the relevant photoinduced applications. However, their irregular derivative phases with lower crystallinity, which could exhibit tempting opportunities for catalytic activities, have long been ignored. Here, the surface-amorphized bismuth oxychloride is produced by homogeneous nanoparticle distribution through a rapid precipitation strategy. Comparing with its surface-crystallized counterpart, the partially amorphized bismuth oxychloride undergoes a fast surface reconstruction process under light irradiation, forming active surfaces with rich oxygen vacancies (OVs), leading to not only distinctive OV-mediated interfacial charge-transfer mechanisms with improved carrier dynamics but also robust water-surface interface with enhanced physical and chemical interaction, thus resulting in enhanced photocatalytic water oxidation. The strategy of optimizing by tuning the interfacial interaction behavior proposed in this work could broaden horizons for establishing more efficient partially amorphized energy conversion materials.

The effect of Fe(iii) ions on oxygen-vacancy-rich BiVO4 on the photocatalytic oxygen evolution reaction

The surface oxygen vacancies could promote the photocatalytic O2 evolution of BiVO4. Simultaneously, Fe3+ ions in solution could facilitate the holes' transfer to improve the water oxidation reaction.