The palladium hydride (Pd-H) system has attracted various studies. Palladium (Pd) has excellent hydrogen selectivity, permeability and hydrogen (H) diffusivity with high mobility. It possesses the capacity to absorb a considerable amount of H at room temperature and atmospheric pressure, and this ability is reversible. Therefore, it has diverse applications such as fuel cells, hydrogen storage, refrigeration, hydrogen separation and purification, nuclear radiation adsorption and catalytic converter. However, the coexistence of low H alpha (α) and high H beta (β) phases in Pd hydride causes a miscibility gap. The strain caused by the lattice mismatch between the two phases increases the possibility of mechanical failure. In addition, Pd is vulnerable to hydrogen embrittlement after some cycles of α phase and β phase transformations in Pd membranes or absorption/desorption cycles in hydrogen storage. Pd membranes are also prone to H2S and CO poisoning. Finally, palladium is an expensive noble metal, with a price currently higher than gold. Pd-Ag alloys possess higher H permeability, solubility and narrower miscibility gap with better mechanical properties than pure Pd, but sulfur poisoning remains an issue. Pd-Cu alloys have excellent resistance to sulfur and carbon monoxide poisoning and hydrogen embrittlement, good mechanical properties, and broader temperature working environments over pure Pd, but relatively lower hydrogen permeability and solubility than pure Pd and Pd-Ag alloys. This suggests that alloying Pd with Ag and Cu to create Pd-Ag-Cu ternary alloys can optimize the overall performance and substantially lowers the cost. To accelerate the search for Pd-Ag-Cu alloys with optimal hydrogen selectivity, permeability, diffusivity, absorption, thermal stability and resistance to sulfur and CO poisoning, an accurate and efficient modeling of the Pd-Ag-Cu-H system is needed. The most reliable simulation technique utilizes first principle (ab initio) calculations, but its high processing costs make it infeasible for simulations contain a large number of atoms. Molecular dynamics (MD) simulations using the embedded atom method (EAM) offers an efficient way to investigate alloys with larger atomic structures. EAM is well suitable to model binary and ternary hydrides with metallic crystal structures and interstitial H atoms. Thus, in this paper, we provide the first embedded atom method potentials for the quaternary hydrides Pd1-y-zAgyCuzHx. The fully analytical potentials are fitted utilizing the central atom method without performing time-consuming molecular dynamics simulations. First principles simulations using SIESTA were carried out to obtain the fitting parameters. The Pd1-y-zAgyCuzHx&nbsp;EAM potentials can capture the preferred H occupancy sites; and predicts the trends for the lattice constants, cohesive energies, and elastic properties during MD simulations. The potentials also captured the existence of a miscibility gap for the Pd1-y-zAgyCuzHx&nbsp;and predicted it to narrow and disappear when Ag and Cu concentration increases as was predicted by the experimental findings

Potentials for PdAgCu Metal Hydrides Energy Simulations

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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