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New Insights on the Formation Process and Thermodynamics of the α‑Phase PdH(D)x through Direct Enthalpy Measurement of H(D) Dissolution

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journal contribution
posted on 09.04.2020, 19:04 by Shun Dekura, Hiroshi Akiba, Osamu Yamamuro, Hirokazu Kobayashi, Mitsuhiko Maesato, Hiroshi Kitagawa
The palladium (Pd)–hydrogen (H) system is one of the most famous hydrogen-storage systems. However, the formation process and thermodynamics at the initial stage of hydrogen storage in Pd remain unclear. Here we report the formation process and thermodynamics of the α-phase PdH­(D)x (x < 0.03) for the first time through direct measurements of the enthalpy of H and D dissolution, −ΔsolH, at around 303 K, with an accurate adiabatic calorimeter under precisely controllable H2(D2) gas pressure. This is the first observation that three steps are involved in the H­(D) dissolution in the α-phase PdH­(D)x: the absorption of H­(D) into trapping sites, the formation of the α phase, and the β-phase nucleation. The determined values of −ΔsolH were significantly larger than the indirectly estimated previous values. With the accuracy and the wide applicability of our methodology, these new insights may pave the way for future developments in hydrogen chemistry.