Measurements of Pressure-Stress Coupling in Hydrated Palladium

Abstract

Hydrogen is considered to be a promising element which has specific energy over 120 MJ/kg highest energy per mass of any fuel. However, its low ambient temperature density leads to low volumetric density, therefore requiring the development of energy storage systems that have potential for higher volumetric density. In this context, we are storing hydrogen within metals by absorption. Here, we report on the stress evolution of metal during hydrogen absorption which is due to the lattice expansion of the hydrogen absorbing phase during hydrogen uptake. The stress induced by material based hydrogen absorption and desorption in very thin palladium layers was recorded in situ using a specially designed cell. Influences of gas pressure, temperature and metal geometry on the stress evolution were considered. In this regard, so called pressure-stress isotherms are proposed in thermomechanical analogy to pressure composition isotherms. The importance of the coupling is discussed in interpreting the hysteresis observed in the pressure versus hydrogen content plots and the role of stress in modifying the maximum hydrogen capacity of a metal hydride under stress.