Engineering multiple optimization strategy on bismuth oxyhalide photoactive materials for efficient photoelectrochemical applications

The photoelectrochemical (PEC) technique, as a simple solar energy conversion device, is one of the most promising solutions for addressing both environmental and energy challenges. PEC technique mainly involves the photoconversion process of photoactive materials through carrier excitation and charge transfer under light irradiation, and the active material plays a central role in the entire system. The design and synthesis of highly PEC active materials is crucial for achieving efficient PEC performance. The photoelectric conversion efficiency of photoactive materials mainly depends on broad range of light absorption response and rapid separation/transfer rate of photogenerated carriers. Common photosensitive semiconductors can be used as photoelectric active materials, including metal oxides, metal sulfides, organic small molecules and organic polymers. However, achieving a high photoelectric conversion efficiency is challenging due to the inherent limitations of using a single semiconductor material. Exploring functional composites with specific structural compositions can overcome the performance deficiencies of individual semiconductor materials. In addition, the ultraviolet region of the solar spectrum accounts for only about 5 ​%, while visible light accounts for approximately 45 ​%. The development of PEC active materials that can be driven by visible light, such as silver, bismuth, and organic polymer materials, is crucial for the commercial application of PEC technique. Due to the characteristics of bismuth oxyhalide BiOX (X ​= ​Cl, Br, I)-based materials, such as an adjustable band gap, a unique layered structure, non-toxicity, a wide light absorption range and outstanding light stability, the PEC technique based on BiOX (X ​= ​Cl, Br, I) has become a popular research topic. In this paper, the physicochemical properties of BiOX (X ​= ​Cl, Br, I)-based materials are reviewed. The methods used to modify BiOX (X ​= ​Cl, Br, I)-based materials from the perspectives of surface and interface are discussed. These modifications aim to improve the utilization rate of sunlight and inhibit the recombination of photogenerated electrons and holes. Additionally, the research progress in microstructure modulation, surface vacancy, functional group modification, metal loading, heteroatom doping and heterojunction construction is emphasized. Through various design strategies, the separation efficiency of photogenerated carriers in BiOX (X ​= ​Cl, Br, I) can be effectively enhanced, thereby improving its performance in PEC applications. The significant contributions of modified BiOX (X ​= ​Cl, Br, I) to various applications, including PEC sensing, PEC water splitting, photoelectrocatalytic degradation, CO₂ reduction, nitrogen fixation and photocatalytic fuel cells are described. Finally, the challenges in the aforementioned applications of BiOX (X ​= ​Cl, Br, I) materials are discussed, and the future research and practical application of BiOX (X ​= ​Cl, Br, I) are prospected.