Thermal stability, hydrogen adsorption and separation performance of Ni-based amorphous alloy membranes

Ni-based amorphous alloy membranes (AAM) with high selectivity and hydrogen permeability were prepared by a novel technique using electroless Ni-plating. The crystallization processes of the membranes were investigated by means of differential scanning calorimetry and X-ray diffraction. The results show that the thermal stability of the Ni–Ru–P AAM is significantly higher than that of the Ni–P membrane, and that the crystallization of the Ni–P AAM proceeds via two steps: (i) from the as-prepared Ni and NixPx to Ni2.55P and; (ii) from Ni2.55P to the more stable Ni3P. Extended X-ray absorption fine structure studies confirmed the existence of a long-range disorder in the as-prepared Ni–P AAMs but no such structure was detected in the Ni–P alloy after crystallization. The results of X-ray photoelectron spectroscopic investigations show that Ni and P both exist mainly in oxidized states (Ni3+ and P5+) on the surface, whereas in the bulk they are in elemental states (Ni0 and P0). After crystallization, phosphorous diffused from the bulk to the surface, increasing the surface P contents. H2-TPD (temperature-programmed desorption) results indicated that the H2 adsorption properties on the Ni–P AAM were completely different from those on the Ni–P alloy membranes after crystallization, suggesting that after crystallization a substantial surface Ni metals lose and so the adsorption sites at low temperature disappear on the surface of the Ni–P membranes. The study of an ethanol dehydrogenation reaction verified that the ethanol conversion observed on the Ni–P AMC reactor decreased due to the deterioration of the H2-adsorption performance.