An x-ray study of palladium hydrides up to 100 GPa: Synthesis and isotopic effects

Abstract

The stable forms of palladium hydrides up to 100 GPa were investigated using the direct reaction of palladium with hydrogen (deuterium) in a laser-heated diamond anvil cell. The structure and volume of PdH(D) x were measured using synchrotron x-ray diffraction. The Pd atoms remain on a f cc lattice. The stoichiometry of the hydride is inferred from the volume expansion due to the hydrogen solubility in the Pd lattice. No evidence for hydrogen to palladium ratio greater than 1 is observed for both isotopes. An inverse isotope effect on the formation enthalpy of the stoichiometric Pd hydride is disclosed by measuring the equilibrium formation pressure of PdH and of PdD, 1.9 GPa and 2.7 GPa respectively. An isotopic shift between the compression curves of PdH and of PdD is also measured, in good agreement with ab initio calculations quantifying the contribution of the hydrogen zero-point vibrational energy. I.

$\mathcal{P}^2$: Combining pressure and electrochemistry to synthesize superhydrides

“…At high pressure (e.g., 150 GPa), the method gives the rocksalt structure as the most probable with a high c-value, indicating that on compression this structure is indeed the ground state predicted at the GGA-level of theory. These results are consistent with experiments reported up to 100 GPa 15,16 .…”

The high-pressure lithium–palladium and lithium–palladium–hydrogen systems

“…The fitted equation of state parameters are given in Table 1 . Both compounds exhibit intermediate compressibility between those of lithium, which is highly compressible 30 , 32 , and palladium, which has low compressibility 20 .

Figure 10 Volume vs pressure plots.

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“…The hydrogen content increases from at formation to at a few GPa 19 . Further compression has not been observed to result in any higher hydride to 20 . A number of lithium palladium intermetallics have been reported at ambient pressure with stoichiometries of , , , , , and 21 .…”

Metal (boro-) hydrides for high energy density storage and relevant emerging technologies

“…Unfortunately, PdH0.6, with a mere hydrogen capacity of 0.57 wt% H, is a typical stoichiometry which can be reached for palladium-hydrogen system near ambient conditions, and there is no evidence for H:Pd atomic ratio larger than 1 even up to 100 GPa [47]. These facts, in addition to the high price of palladium, exclude PdHn from broader applications in hydrogen storage; however, due to its excellent reversibility, palladium tritide PdTx, remains a common tritium reservoir in nuclear facilities [48,49].…”