Analysis and improvement of cyclic stability of H2 sensing properties of Pd/Mg–Ni films

The nominal electrical resistivity of palladium coated magnesium–nickel (Pd/Mg–Ni) films was measured by exposing the films iteratively to hydrogen (H2) at a concentration of C H 2 for hydrogenation and air for dehydrogenation. When a low C H 2 was used, the film remained in an amorphous α-phase. H atoms interacted “interstitially” with the atomic network, and the H2 detection sensitivity S was relatively stable in the cyclic test. If higher C H 2 values were used, the film was partially or completely transformed to an amorphous β-phase. Significant volumetric breathing occurred in the course, leading to severe roughening of the film and oxidation of the Mg–Ni layer. S became unstable. These suggestions are supported by the results of film thickness measurements, atomic force microscopy and X-ray photoelectron spectroscopy analyses. Stability of S of a Pd/Mg–Ni film can be greatly improved by either (i) operating the film in a low C H 2 environment to prevent substantial volume breathing, or (ii) choosing an appropriate thickness of the Pd layer to optimize both oxidation resistance and sensing response of the film sensor.