Hydrogen diffusion on and into the hydrogen-covered Pd(100) surfaces from first-principles

We present a study of hydrogen interaction with some hydrogen-covered Pd(1 0 0) surfaces at different coverage by using DFT-based microkinetic modeling. Two different mechanisms into the subsurface regions of the hydrogen-covered Pd(1 0 0) surfaces are found as monomer and dimer permeation pathways. At low coverage, the interaction of hydrogen-hydrogen strongly increases the hydrogen adsorption energy and surface diffusion/ permeation barrier. However, the saturated Pd(1 0 0) surface yields a favorable pathway for the formation of subsurface hydrogen species via the dimer permeation pathway. DFT-based microkinetic modeling further re-veals that hydrogen flux through the hydrogen-covered Pd(1 0 0) surfaces has distinct temperature dependence with respect to different coverage.