The kinetics of hydrogen permeation across Pd0.47Cu0.53 metallic membranes were reported. The permeation mechanism was a multi-step process including surface chemisorption of molecular hydrogen (upstream side of the membrane), hydrogen diffusion across bulk regions, hydrogen recombination (downstream side of the membrane) and evolution. The role of different operating parameters (temperature, surface state, sample microstructure) was analyzed and discussed using both time and frequency domain experiments. Experimental pneumato-chemical impedance diagrams show that there was no significant rate-limitation at surfaces, except at low temperatures close to room temperature. Diffusion-controlled transport of hydrogen across the membrane was rate-determining. However, the value of the hydrogen diffusion coefficient does not rise exponentially with operating temperature in the 40–400C temperature range under investigation, as expected for a thermally activated diffusion process. At temperatures as low as 300C, new rate-limitations appear. They could be attributed to recrystallization and/or phase transformation processes induced by temperature and the presence of hydrogen.

Time and Frequency Domain Analysis of Hydrogen Permeation Across PdCu Metallic Membranes for Hydrogen Purification. C.Decaux, R.Ngameni, D.Solas, S.Grigoriev, P.Millet: International Journal of Hydrogen Energy, 2010, 35[10], 4883-92