Controlled Doping Sites to Enhance Charge Transfer of ZnO for Ultrarapid Methane Sensing

Charge transfer in metal oxide semiconductor-based sensitive materials plays a crucial role in gas sensing. Doping engineering is an effective approach to optimize the electrical properties of oxides for enhanced sensing performance. However, the underlying mechanism by which doping sites affect gas sensing performance remains not well-known. In this study, Al-doped ZnO nanorods with controlled doping sites (interstitial- and substitutional-dominant) were successfully fabricated via a mild (80 °C) and facile (30 min) liquid-phase route for CH₄ sensing. Direct atomic-scale observations showed that the doping Al site in ZnO shifted with increasing doping amount from interstitial-dominant to substitutional-dominant. The density functional theory results revealed that interstitially Al-doped ZnO realized more free ZnO electrons than pristine and substitutionally Al-doped ZnO, facilitating the generation of chemisorbed oxygen for CH₄ activation and electron transfer during the sensing process and thus resulting in ultrarapid CH₄ sensing with response and recovery times of 3.8 and 5.0 s, respectively.