Significantly enhanced hydrogen sensing in rare-earth doped indium oxide nanofibers via metal orbital hybridization

Rare earth elements often serve as catalysts for the redox reaction between oxygen (O₂) and the target gas. In particular, the Ce doping can contribute effectively to the humidity resistance of the sensors due to the Ce^{3 +} ions. Unfortunately, the Ce doping often results in a low enhancement of the sensor response. In this work, Pd, Ce co-doped indium oxide (Pd/Ce-In₂O₃) nanofibers were designed and prepared via the traditional electrospinning technique. Results showed that Pd/Ce co-doping created more oxygen vacancies and smaller grains within the In₂O₃ skeletons. As expected, H₂ sensing tests indicated the Pd/Ce-In₂O₃ sensor shows the maximum response value of 41.13–10 ppm hydrogen at 280ºC, approximately 1.85 and 4.27 times those of the Pd-In₂O₃ and Ce-In₂O₃ ones, respectively. Even at 80ºC, this sensor still shows a response of 1.85. More interestingly, the Pd/Ce-In₂O₃ sensor also shows fast response/recovery rates (< 1 s / 5 s), excellent gas selectivity, and high long-term stability, as well as excellent anti-humidity properties. In addition, further analysis of the gas sensing enhancement mechanism indicates that the orbit hybridization of Ce (f) and Pd (d) not only increases the adsorption property of In₂O₃ to H₂, which primarily contributes to the response, but also enhances the catalytic property of Pd/Ce composites and the transfer of sensing electrons from the catalyst to In₂O₃ matrix, benefiting the response value, response speed and humidity resistance of the sensors.