Effectively Improved CH₄ Sensing Performance of In₂O₃ Porous Hollow Nanospheres by Doping with Cd

Recently, due to the promising application of metal oxide semiconductors in high-performance methane (CH₄) sensors, more attention has been paid to the development of feasible strategies for improving CH₄ sensing performance. Herein, we present a strategy of cadmium (Cd) doping to improve the CH₄ sensing property of In₂O₃ porous hollow nanospheres (PHNSs). The Cd-doped In₂O₃ PHNSs were prepared via an impregnation-calcination approach with self-made carbon nanospheres as a hard template. The samples were characterized by various techniques to evaluate their structure, morphology, surface state, composition, and band gap. When applied as a sensitive material in the CH₄ sensor, the Cd-doped In₂O₃ PHNSs, compared with bare In₂O₃ PHNSs, showed some significant improvements in performance, especially a reduced operating temperature (200 °C vs 300 °C), an enhanced response (9.5 vs 2.5 for 500 ppm of CH₄), a faster response speed (16 s vs 276 s), and better selectivity. In addition, the Cd-doped In₂O₃ sensor can also maintain a commendable long-term stability, and the range of its response amplitude within 30 days is only 6.3%. The sensitization effects of the Cd dopant on the In₂O₃ PHNSs are discussed.