Insights into Selective Sensitivity of InO-CuO Heterojunction Nanocrystals to CH over CO and H: Experiments and First-Principles Calculations.

Metal oxide semiconductor gas sensors have demonstrated exceptional potential in gas detection due to their high sensitivity, rapid response time, and impressive selectivity for identifying various sorts of gases. However, selectively distinguishing CH from those of CO and H remains a significant challenge. This difficulty primarily stems from the weakly reducing nature of CH, which results in a low adsorption response and makes it prone to interference from stronger reducing gases in the surroundings. Herein, we synthesized InO-CuO nanocomposites using a hydrothermal method to explore their gas sensing properties toward CH, CO, and H. Characterization tests confirmed the successful preparation of InO-CuO nanocomposites with different In:Cu molar ratios and the formation of a p-n heterojunction. The gas sensing test results indicated that the InO-2.1CuO nanocomposites calcined at 500 °C and measured at 350 °C displayed a p-type response for CH and an n-type response for CO and H, allowing for accurate differentiation of CH from CO and H. Moreover, the InO-2.1CuO sensor also showed excellent stability and reproducibility across all three gases. First-principles calculations revealed distinct changes in the electronic structure of the InO-CuO heterojunction upon adsorption of CH, CO, and H, a finding that aligns with empirical evidence. The gas selectivity mechanism was effectively explained by variations in the energy band gap, driven by electrical behavior during the adsorption process. This work suggests a promising approach for developing selective gas sensors capable of detecting weakly reducing gases.