Uptake,transport, and release of hydrogen from Pd(100)

Understanding the interactions of hydrogen atoms with the surface and the subsurface regions of Pd is critical to the development of advanced energy technologies for hydrogen storage, hydrogen separations, and catalytic conversion processes. While many of the physical and chemical characteristics of the H₂–Pd system are known, the kinetics and thermodynamics of H atom absorption into the bulk, transport from the bulk back to the surface, and desorption from the surface remain unclear. In this work, the kinetics of D₂ release from Pd following exposure to D₂ over a range of pressures and temperatures were measured using temperature programmed desorption. To accurately simulate the kinetics of D₂ release, the continuum-based model of Mavrikakis, et al. (J. Chem. Phys 105, 8398, 1996) was extended to include activation barriers for desorption and transport that depend on D atom concentration in the surface, subsurface and bulk regions of the Pd. The use of concentration dependent barriers improves the ability of the model to predict the hydrogen uptake and release kinetics observed across temperatures ranging from 100 to 600 K.