My understanding is that catalytically-active surfaces that can work have the following properties:
- Efficiently dissociate molecular hydrogen to H atoms;
- Collect the dissociated H atoms in large densities in an adsorbed state;
- Do not strongly bind with the dissociated H atoms.
Platinum group metals like are generally good for point 1, but metallic Ni catalysts for hydrogenation reactions exist too, so they are not necessarily excluded from the process. Metal mixtures may be useful if they make for a more efficient catalyst improving points 1-2, but probably not so much if they form hydrides (e.g. Pd in bulk form), thus going against point 3.
However, the usage of purely metallic catalysts appears to be intended as a combination of carbon+metal surfaces, with possibly iridium as an exception to this. https://doi.org/10.1016/j.ijhydene.2021.02.221
Many transition metals like platinum, nickel and iron dissolve carbon at high temperature. This carbon segregates to the surface at lower temperature . A heat treatment or temperature cycling gives a carbon layer on the metal surface. Thus such a metal surface is in effect similar to a carbon surface (see above). With a partial carbon layer, the remaining clean metal areas are dissociative (provide dissociation centres) for hydrogen and the carbon covered areas promote Rydberg state desorption, thus together giving a working H(0) catalyst.
In the patent application discussed in this thread, nickel is an example of catalytically-active metal listed as suitable for absorbing the ultra-dense hydrogen produced. https://patents.google.com/patent/US20190371480A1/
[...] Advantageously, the metallic absorbing member may be made of at least one material selected from the group consisting of a metal in a liquid state at an operating temperature for the apparatus, and a catalytically active metal in a solid state at the operating temperature for the apparatus.
Examples of suitable materials for the metallic absorbing member include liquid or easily melted metals like Ga or K, and solid catalytically active metals like Pt or Ni etc.
A mixture (or perhaps a layered combination) of various metals and non-metals having different functions will possibly be more useful or efficient for the process, but there have not been specific studies or patent applications for this, only hints and suggestions.