The very extensive literature on hydrigenation shows that both ultrasonics and acid cleaning of nickel (and other metals) increase the absorption and adsorption of hydrogen. The reason being that completely oxide free surfaces reduce H2 to H+H more readily than 'dirty' ones. One of the steps in the hydrogen uptake process may be the formation of 'transient' hydrides, which actually penetrate the metal, propagating crack defects as they do so. This process of defect creation is thought to be due to both physical swelling caused by the hydrides, and charge differences between materials.The hydrogen makes its own defect sites.
In the just published JCMNS20 compendium Storms publishes his newest findings about Pd surface cleaning with HNO3 (the classical way to do it!).
JCMNS20 http://lenr-canr.org/acrobat/BiberianJPjcondenseds.pdf
Now, after cleaning, Pd shows new effects, one beeing the fact that the D/Pd load ratio is "not at all" important for excess heat. The mfp finding that the release of D produces the effect is more ore less confirmed now for Pd too. But for Pd it could well be, that the LENR fusion runs on internla surfaces where as in Ni we claim it's happening close to the surface.
Initial high load is still important, because it completely changes the internal structure of Pd!!