The hydrogen diffusion coefficient in palladium was evaluated here as a continuous function of the equilibrium hydrogen pressure. The results revealed a decreasing diffusion coefficient with pressure, in contrast to an increasing permeability and solution coefficient. The diffusion coefficients were described by:

intrinsic:     D(m2/s) = 2.40 x 10-7exp[-21.1(kJ/molH)/RT]

100kPa:     D(m2/s) = 3.14 x 10-7exp[-22.7(kJ/molH)/RT]

500kPa:     D(m2/s) = 5.53 x 10-7exp[-26.2(kJ/molH)/RT]

H/M = 0.04:     D(m2/s) = 3.85 x 10-7exp[-24.5(kJ/molH)/RT]

This study did not assume constant hydrogen mobility, but evaluated the mobility as a function of pressure. This precise analysis revealed a slightly increasing mobility with pressure, because of less deep hydrogen potential at higher hydrogen concentrations.

Hydrogen Diffusion Coefficient and Mobility in Palladium as a Function of Equilibrium Pressure Evaluated by Permeation Measurement. S.Hara, A.Caravella, M.Ishitsuka, H.Suda, M.Mukaida, K.Haraya, E.Shimano, T.Tsuji: Journal of Membrane Science, 2012, 421-422, 355-60