Understanding and Quantifying the Contribution of Oxygen Species in Hydrogen Sensing by Pd/In₂O₃ Nanosheets

Conventional metal oxide semiconductor (MOS) hydrogen sensors rely on surface oxygen-mediated redox reactions, while the distinct contributions of each type of oxygen species, including weakly adsorbed oxygen (O_W), strongly adsorbed oxygen (O_S), and lattice oxygen (O_L), to sensing performance remain poorly understood, hindering the rational design of sensing materials. Here, through precisely controlling Ar pre-treatment at tailored temperature and calculation of electron transfer numbers, we quantitatively study the distinct oxygen species contributions of the gas-sensitive Pd-decorated In₂O₃ (Pd-In-O) nanosheets during the H₂ sensing process, and O_S species are found to play a crucial role in hydrogen sensing. The in situ characterizations reveal that the oxygen vacancies boost the activation and mobility of O_S species and optimize the d-band center of Pd, further promoting the reaction kinetics and accelerating the hydrogen spillover from Pd to In₂O₃. Additionally, the surface oxygen species of Pd-In₂O₃ with varying activities are rationally designed, and the Pd-In-O sample with the highest activity demonstrates a robust H₂-sensing performance even at room temperature (R_a/R_g = 20.1 to 200 ppm H₂ at 25 °C). The as-fabricated sensor is further applied for real-time detection of the simulated hydrogen leakage in the laboratory.