Effect of humidity interference on NO2 gas sensing of In2O3 nanoneedles at moderate operating temperature

This study employs both experimental and computational methodologies to examine the gas-sensing performance of needle-like In2O3 nanosensors towards a model NO2 gas in dry (10 % RH) and wet (99 % RH) environments. The single crystalline nanoneedles exhibit distinct surface facets, primarily (110) or (111) crystalline planes, spanning a wide aspect-ratio range of 3.9-7.0. At a relatively low operating temperature of 50 degrees C and NO2 gas concentration of 10 ppm, the experimental assessment yields sensing-response ratios (i.e., S-wet/S-dry) of 0.19 +/- 0.18 and 0.23 +/- 0.07 for In2O3 nanoneedles featuring (110) and (111) surfaces, respectively. Notably, density-functional theory computations reveal that the adsorption energies of NO2 molecules on both In2O3 (110) and (111) surfaces significantly weaken under moist conditions. A relatively stronger adsorption affinity is observed on the (110) surface than the (111) counterpart. Our calculated electronic band structures reveal conspicuous changes in conductivity upon the adsorption of NO2 and water vapor on the In2O3 surfaces. The observed variations in conductivity, in conjunction with the adsorption-energy calculations, offer valuable insights into the structural mechanisms underlying the experimentally observed sensing-response alterations in humid environments.