Hydrogen gas sensing performance of Pd–Ni alloy thin films

We investigated the hydrogen (H2) sensing properties of palladium (Pd)–nickel (Ni) alloy films with varying Ni content and discussed them in light of structural deformations. The Pd–Ni alloys operated reversibly upon H2 absorption and desorption and their sensitivities decreased linearly with Ni content added to Pd. This was attributed to reduction in the lattice constant and interstitial volume caused by the Ni addition, allowing fewer hydrogen atoms to penetrate into the Pd–Ni alloy with higher Ni content. Interestingly, the response time of the Pd–Ni alloys was much shorter than that of pure Pd, presumably due to the fast permeation of hydrogen atoms through microscopic imperfections in the alloys. Unlike pure Pd, the Pd–Ni alloys showed an almost linear relationship between the sensitivity and H2 concentration without hysteretic behaviors, enabling the detection of low concentration of H2 down to 0.01%. These results provide a significant understanding of the role of Ni in the Pd–Ni thin films for improving the H2 sensing properties of the Pd-based alloy film sensors.