Defect-driven material design for high-performance semiconducting gas sensing applications

The development of gas sensors over the past two decades has been remarkable. Growing concerns over poor air quality and increasing commercial demand have driven researchers to innovate more efficient gas sensing technologies across various fields, including environmental monitoring, medical diagnostics, food safety, and industrial production. However, the performance of existing pristine materials remains inadequate to meet the requirements of high selectivity, sensitivity, and stability. To address this, defect engineering has emerged as a crucial strategy for modifying and enhancing material properties. Defects disrupt a material's symmetry, and the goal is to design the 'perfect defect '—removing detrimental defects while introducing beneficial ones that improve the structure–function relationship of sensing materials. These improvements span their electronic structure, atomic and molecular-level interactions, specific surface area, and metal–oxygen bonding. While defect influences are pivotal in many applications, their effective implementation in gas-sensing materials requires a deeper understanding of defect formation and precise control of defects. This review explores the role of defect manipulation in semiconducting gas sensors, systematically categorizing defects such as point defects, vacancies, substitutions, surface defects, grain and twin boundaries, as well as line and volume defects, based on their dimensional characteristics. We analyze their effects on material performance and detail various strategies for defect generation. The review highlights and summarizes key literature from the past decade, emphasizing defect-induced transformations in materials such as metal oxides, metal nitrides, carbon nitrides, and 2D materials (including graphene, black phosphorus, transition metal dichalcogenides, and MXenes). Furthermore, the review identifies current challenges and offers future perspectives for advancing defect design in gas sensor applications.