Review—Recent Material Advances and Their Mechanistic Approaches for Room Temperature Chemiresistive Gas Sensors

Gas sensors have become an integral part of the industrial and domestic sector, due to the increased emissions from industries, automobiles, and thereby exposure of the harmful gases like CO, NO ₂ , SO ₂ , CO ₂ , NH ₃ etc. Metal oxide-semiconducting (MOS) chemiresistive gas sensors are the most popular commercial gas sensors available in the market. However, they need high operational temperature for activation and deactivation, which is a serious concern for sensitive combustible environments, as well as in other applications where flexibility, low power consumption, and miniaturization are desirable. Hence, gas sensors those exhibit high sensitivity and selectivity to the target gases, at room temperature are the need-of-hour in the market. This review focuses on various strategies and approaches those being employed and the challenges ahead to realize such room temperature chemiresistive gas sensing; viz: (i) 1 D-nanostructuring of various conventional metals and metal oxides ; (ii) Nano +heterojunctions between metal oxide-metal oxides and noble metals ; (iii) 2 D-materials ; (iv) Self-heating in nanowires ; (v) Perovskites ; (vi) Conducting polymers ; (vii) defect engineering to produce free charge carriers, and (viii) alternative activation by light illumination . The mechanism behind the strategies implemented to achieve such room temperature gas sensing has been explicitly discussed. The review also introduces various types of gas sensors, their working principle, pros and cons, mechanism and parameters of chemiresistive gas sensors, and their typical construction. This article also discusses the electrode configurations used in the chemiresistive gas sensors.