Metal–Organic\nFramework-Derived Ni-Doped Indium\nOxide Nanorods for Parts per Billion-Level Nitrogen Dioxide Gas Sensing\nat High Humidity

Detecting parts per billion (ppb)-level nitrogen dioxide\nin high-moisture\nenvironments at room temperature without reducing sensing performance\nis a well-recognized significant challenge for metal oxide-based gas\nsensors. In this study, metal–organic framework-derived nickel-doped\nindium oxide (Ni-doped In<sub>2</sub>O<sub>3</sub>) mesoporous nanorods\nwere prepared by a solvothermal method combined with the calcination\nprocess. The sensors prepared using the obtained Ni-doped In<sub>2</sub>O<sub>3</sub> nanorods showcase an ultrahigh response, low detection\nlimit, and excellent selectivity. Moreover, the abundant active sites\ntriggered by nickel doping and the capillary enhancement effect caused\nby mesopores endow the sensor with ppb-level (20 ppb) NO<sub>2</sub> detection capability in high-moisture environments (95% RH) at room\ntemperature. With the increase in humidity, the carrier concentration\nof the sensor increases, and the nitric acid generated by nitrogen\ndioxide dissolved in water can be completely ionized in water and\nhas high conductivity. Therefore, the gas response of the sensors\nincreases with the increase in humidity. This study establishes a\npromising approach for the development of trace nitrogen dioxide-sensing\ndevices that are resilient in high-humidity environments.