Effect of surface coating element on hydrogen permeability of melt-spun Ni40Nb20Ta5Zr30Co5 amorphous alloy

The effect of the surface coating element on hydrogenation and hydrogen permeation of a Ni40Nb20Ta5Zr30Co5 amorphous alloy membrane was investigated. A Pd-coated membrane absorbed hydrogen almost to saturation within the initial 20 s of measurement at 573 K. On the contrary, a Ni-coated membrane displayed a much slower hydrogen absorption rate. The Pd-coated sample exhibited hydrogen permeation one order of magnitude larger than the Ni-coated sample. Ni-coated samples showed more significant degradation of permeation flux at 673 K than the Pd-coated samples, because Ni atoms can diffuse into the membrane more easily than Pd atoms, resulting in faster degradation of catalytic activity for the Ni-coated sample than the Pd-coated sample. Furthermore, it was found that the element deposited on the lower-stream side surface of the membrane affected the promotion of hydrogen permeation more significantly than that on the upper-stream side surface. The hydrogen permeation of the sample with Ni coated on the lower-stream side surface of the membrane was much smaller than that with Pd coated on the lower-stream side surface. This observation suggests that the recombination of two H atoms and emission of H2 molecules can be the significant barrier to hydrogen permeation. Therefore, it was concluded that the hydrogen concentration gradient in the membrane and the reaction on the lower-side surface affected the hydrogen permeability of the membrane.