CxNy-based materials as gas sensors: Structure, performance, mechanism and perspective

•The structures, properties, performance, applications, and design-strategies of CxNy-based materials in gas sensors are reviewed.•The DFT-based mechanisms of improved gas sensing properties from each strategy are discussed.•Future prospects and challenges of CxNy-based materials in gas sensing are proposed. Carbon nitride (CxNy) materials, characterized by an ordered two-dimensional without metal ions structure high N:C ratio, phase transition transformation, predispose them for promising applications in catalytic reaction, flexible electronics, broadband photodetectors and battery. However, up to now, its potential advantages in gas sensor applications have yet to be fully explored. This review provides a comprehensive overview of recent advances in CxNy-based materials applied as gas sensor substrates covering structure, properties, synthesis methods, and enhancement strategies. A rigorous assessment of their gas sensing capabilities, including sensitivity, selectivity, and stability was critically summarized. Additionally, the molecule-level mechanistic aspects underlying the gas-sensing working principles and insights into gas-sensing functional properties were discussed. Furthermore, thorough investigations utilizing density functional theory (DFT) studies, aimed a illuminating the fundamental principles governing the gas-sensing behavior of CxNy-based materials, were be presented in detail. Finally, futuristic gas sensing applications along with challenges of CxNy were deliberated herein.