Tunable NH₄F-Assisted Synthesis of 3D Porous In₂O₃ Microcubes for Outstanding NO₂ Gas-Sensing Performance: Fast Equilibrium at High Temperature and Resistant to Humidity at Room Temperature

NO2 gas sensors based on metal oxides under wild conditions are highly demanded yet an incomplete surface reaction and humidity interference on the gas-sensing performance limit their applications. Herein, we report three-dimensional (3D) porous In2O3 microcubes via a simple hydrothermal strategy to produce outstanding NO2 gas-sensing performance: fast equilibrium of the surface reaction at 150 °C and negligible humidity dependence on the NO2 gas sensing at room temperature. The 3D porous In2O3 microcubes with high surface areas, suitable pore sizes, rich oxygen vacancies, and high conductivity are testified. The underlying structural transformation mechanism for 3D porous In2O3 is investigated in detail. The as-made 3D porous In2O3 microcubic gas sensors present excellent gas-sensing performance to 50 ppm NO2 at 150 °C, including a high response value (2329), fast response/recovery time (10/9 s), a low detection limit (10 ppb), long-term stability (60 days), and strong selectivity. Furthermore, they exhibit relatively stable NO2 gas response under humidity variation (20–80%). The NO2 gas mechanism under the interference of water is also clarified.