Tailoring the injection action of oxygen over top-surface of bismuth sulfide to change reactive electron transfer path for flexible NO2 sensors

Precisely tailoring the surface electronic state of catalysts to realize the optimal design of adsorption sites is essential to the surface-related gas-sensing reaction. Herein, based on both molecular orbital theory and p-band models, we develop a brilliant surface oxygen-injected method to simultaneously enhance the overlap of energy-level alignment (ELA) and reduce the anti-bonding filling (ABF) level between surface Bi p-band and adsorbed NO₂ molecule, leading to an optimal NO₂ adsorption mode and sensing performance. By controlling the oxygen permeation concentrations, the weak-oxidized Bi₂S₃-200 catalysts with ordered core/disordered shell configuration exhibit excellent NO₂ gas sensitivity (12.5 % to 1 ppm) and low experimental detection limit (100 ppb), surpassing that of most reported NO₂ sensors. Ex situ XPS characterizations further demonstrate that the weak-oxidized amorphous Bi species can serve as active adsorption centers to alter the electron transfer path in NO₂ atmosphere. Finally, through inserting flexible MEMS sensors array into multifunctional wireless sensing device, the Bi₂S₃-200 sensors can realize real-time NO₂/temperature/humidity monitoring and cloud data transmission at room temperature, which thereby pave the way for the development of crop health monitor and precision agriculture.