Extending the Life of Palladium Beds

A principal objective of the WSRC research is to extend the useful life of the palladium storage medium. The palladium-hydride storage process in batteries and other storage technologies is cyclic. "Hydrogen is loaded into the metal-hydride," explains Wolf, "and then desorbed back off, through as many as 10,000 cycles. You keep absorbing and desorbing hydrogen, or charging and discharging, and like a sponge getting wet and drying out over and over again, it expands and contracts. Over time the material begins to break down."

By understanding this breakdown at the level of atoms, the researchers hope to find solutions. Palladium in reality, for instance, is seldom a perfect crystal. Like the grain in wood, it has grain boundaries and dislocations. As the metal expands and contracts over time, it's apt to fracture at grain boundaries. An additional wrinkle is that tritium stored in a metal decays radioactively to helium, which becomes trapped in the material and forms new defect sites. "For some reason," explains Mansour, "the helium stays in, creating a permanent deformation in the palladium crystal structure that alters the material's performance."

The researchers want to simulate this complex process. Mansour sees it as a multi-step objective: "We want to understand how dislocated palladium behaves. We then want to understand how the dislocated material acts in the presence of hydrogen. Then, we'd like to understand how it behaves with helium. The next step would be to put hydrogen and helium both in there, which is what happens in real life. These studies are underway, and this is what we're doing on the T3D."

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