What is so special about metallic Pd that it can absorb around 900 times its own volumes of hydrogen? I was searching articles, but I couldn't find an answer to this question. All researchers say that Pd is called a "hydrogen sponge", it forms alpha and beta-hydride depending on hydrogen pressure and concentration, that PdHx is a p-type semiconductor, alloying Ag and Pd could further increase the hydrogen absorption, etc. It is a statement of facts rather than an explanation. Other transition metals also form hydrides - Pt, Ni, Ag, etc. But what makes Pd so special? Maybe this happens due to Pd's electronic configuration, or its crystal lattice, electron affinity, or a combination of different factors?
Good question.
The only thing I can contribute it that PdH0.75 is an alloy rather than a hydride:
(a) S. Li, Y.-Z. Chen, Y.-K. Cao, F. Liu, Acta Metall. Sin. (Engl. Lett.) 2016, 29, 120-128
(b) S. K. Konda, A. Chen, Mater. Today 2016, 19, 100-108.
Adsorption of hydrogen in palladium occurs because of increased in volume by three fold.
Dear Oleksandr, thank you for asking this very interesting and important technical question. In fact, palladium could play an important role in future hydrogen technology. In this context I suggest that you have a look at the following interesting article which is freely available as public full text right here on RG:
The role of palladium in a hydrogen economy
Article The role of palladium in a hydrogen economy
For more general information about this phenomenon please also see the instructive Wikipedia entry on "Palladium hydride" at
https://en.wikipedia.org/wiki/Palladium_hydride
This article has some useful references to original research articles about the topic.
Good luck with your work and best wishes!
Dear Oleksandr,
This property of palladium is apparently explained by the electronic structure of this atom. On the outer layer of this atom, unlike Pt and other elements, there are no outer electrons, the s and p orbitals are empty, so it has many easily accessible vacancies for the introduction of hydrogen atoms. Pd absorbs hydrogen in a volume ratio of 1: 900. This property of Pd is widely used as a catalyst, for example, in the synthesis of hydrogen halides.
Dear Olekasndr,
Prof. Edelmann and many have given very useful information along with some reading materials. In fact dissociation of HH bond prior to its adsorption on palladium surface requires little or no activation energy barrier, this is in contrast to other metals. Why is this? Please read the articles provided by Prof. Edelmann.
Kind regards
Balakrishna
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