There are several other potential substrates besides palladium. Nickel, titanium, tungsten, and some hydrogen-absorbing compounds. “Hydrogen-absorbing” is a critical feature. I wish more effort was put into investigating tungsten. “Back in the day”, when Langmuir was researching fill gases for light bulbs, he was sure that he was seeing “over unity” values when hydrogen was used as a fill gas.
Unfortunately, Niels Bohr convinced him (on “theoretical” grounds) that “over unity” was impossible. So Langmuir dropped that line of inquiry. Langmuir was a consummate experimentalist....instruments died when Bohr entered a room. I would bet that Langmuir was right.
Tungsten is like $40 a TON........................