Effects of Surface Vanadium Species on the Hydrogen Permeability through Vanadium Membrane without Palladium-Catalyst Overlayer

Abstract

The effects of surface V species on the hydrogen permeability through V membrane without Pd-catalyst overlayer are investigated by the hydrogen permeation test at 773 K and the XPS measurement. The steady-state hydrogen permeation flux through Pd-coating free V membrane after the redox treatment is more than twice that of the non-treated membrane. The hydrogen flux after 50 hours, however, are almost the same regardless of the redox treatment since the redox-treated membrane is deactivated during the hydrogen permeation test. The fraction of V 0+ / V2p 3/2 on the surface of membrane just after the redox treatment is approximately 2%, and the amount of V 3+ is larger than V 4+. This fine balance of the V species composition on the surface is found to induce the high hydrogen permeability. The composition of V species on the surface of the redox-treated membrane changes to V 3+ < V 4+ by oxidation of V 3+ to V 4+ during the hydrogen permeation test for a long time. The loss of the fine balance in the composition of V species is considered to be the cause of the degradation of hydrogen permeability.

Synthesis of Highly Activated Magnesium by Niobium and Tantalum Gel Oxide Catalyst

“…29) In addition, Shirasu et al reported that the multi-valence state of transition metals was important for the catalytic effects of the reaction with H 2 in the case of the vanadium membrane. 30) Based on the analogy of this report, it is possible that the balance of the existing Nb valence states is effective for obtaining a highly active state as the catalyst. It is evident from the above-stated results that reduction states are important for obtaining high catalysis on Nb oxide for the hydrogen absorption and desorption reaction of Mg.…”