Hydrogen response of porous palladium nano-films

Nanostructured Metal Hydrides for Hydrogen Storage

“…In hydrogenography, visible light is used on materials that transition from reflective metals to opaque or transparent hydrides upon hydrogenation, utilizing a property that also has applications in switchable mirrors and windows. , IR emission also has been employed, monitoring changes in intensity over time and even over area as a material is cycled . The IR emissivity depends on the electrical resistivity, which decreases as a metal is hydrogenated to a semiconducting or insulating hydride, and is itself often used as a measure of uptake. , XRD is another commonplace indirect analysis method and is sensitive to both small changes in lattice parameter, at low hydrogen contents, to complete structural transformations from the metal crystal structure to that of the hydride. For thin films, grazing angle, also known as glancing incidence, XRD is employed so that the X-ray beam samples the film preferentially, rather than the substrate.…”

“…Layered films are also quite feasible, particularly with immiscible metals, though the formation of intermetallics can be limited even between alloying metals by avoiding or limiting annealing, leading to distinct layers with minimal blending. Wet chemical methods have also been employed, using preformed NPs and casting them into a thin film . Metal hydrides are too sensitive for the ablative techniques described above, and they would decompose into hydrogen and the other constituent elements instead.…”

“…Hydrogenation was slowed in the films due to in-plane strain and clamping effects that were absent in the NP layers which had interparticle gaps. Using sub-10 nm Pd NPs synthesized by reduction from PdCl 4 2– with ethylene glycol and dropcast onto glass, Gupta et al found that the change in resistivity was dominated by the geometric effect of the Pd particles expanding to form the hydride, which has a larger lattice parameter, and the electronic effect of making them less metallic had a lesser absolute effect …”

“…Wet chemical methods have also been employed, using preformed NPs and casting them into a thin film. 234 Metal hydrides are too sensitive for the ablative techniques described above, and they would decompose into hydrogen and the other constituent elements instead. Therefore, hydrogen is introduced to the metallic films after they are formed.…”

“…28 The IR emissivity depends on the electrical resistivity, which decreases as a metal is hydrogenated to a semiconducting or insulating hydride, and is itself often used as a measure of uptake. 230,234 XRD is another commonplace indirect analysis method and is sensitive to both small changes in lattice parameter, at low hydrogen contents, to complete structural transformations from the metal crystal structure to that of the hydride. For thin films, grazing angle, also known as glancing incidence, XRD is employed so that the X-ray beam samples the film preferentially, rather than the substrate.…”