Improvement and stabilization of optical hydrogen sensing ability of Au-Pd alloys.

Formation of metal hydrides is a signature chemical property of hydrogen and it can be leveraged to enact both storage and detection of this technologically important yet extremely volatile gas. Palladium shows particular promise as a hydrogen storage medium as well as a platform for creating rapid and reliable H optical sensor devices. Furthermore, alloying Pd with other noble metals provides a technologically simple yet powerful way of enacting control over the structural and catalytic properties of the resultant material. Similarly, in addition to alloying, different top-down and bottom-up Pd nanostructuring methods have been proposed and investigated specifically for creating optical H sensors. In this work it was determined that the hydrogen sensing ability of a series of Pd-Au alloy films could be improved by way of a hydrogen over exposure (HOE) treatment. Structural investigation showed that the HOE treatment, in addition to irreversibly altering the film morphology, results in a 1 to 2% expansion in the lattice constant of the metal. By combining a cyclic HOE treatment and alloy aging through annealing, the hydrogen detection sensitivity and response rates of Pd-Au films could be stabilized so that their performance would no longer be appreciably affected by repeated hydrogen uptake and release cycles. This work takes a further step towards routine all-optical detection of part-per-million level hydrogen gas concentrations in Pd-Au alloy films and discussion of ways to enhance response rates is provided.