Hydrogen sensing of nanoporous palladium films supported by anodic aluminum oxides

Nanoporous Pd films supported by porous anodic aluminum oxides (AAOs) were investigated regarding their performance in detecting hydrogen gas with concentrations up to 1% in nitrogen at room temperature. Compared with dense Pd films that usually have very slow responses, nanoporous Pd films based on AAOs were found to have a quick and reversible response due to their enhanced absorption and disorption of hydrogen. Using thinner nanoporous films, concentrations of hydrogen as low as 250 ppm can be detected and a much higher sensitivity, up to 12% resistance variation, was obtained. Two competing hydrogen-sensing processes, the phase-induced increase of film resistance and the break-junction-induced decrease of film resistance, were found in the nanoporous Pd films upon absorption of hydrogen.