Some metal hydrides permit reversible storage and release of hydrogen for a hydrogen using power-generator. But the surfaces of some metal hydrides or metal hydride precursors may be oxidized or have other coatings that inhibit hydrogen absorption or release. Such materials may be suspended in a suitable liquid of supercritical carbon dioxide or liquid nitrogen and subjected to cavitation processing to break up such hydrogen impermeable surfaces or to fracture the particles so as to provide fresh hydrogen penetratable surfaces.