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 V⁰⁺/V2p_3/2 on the surface of membrane just after the redox treatment is approximately 2%, and the amount of V³⁺ is larger than V⁴⁺. 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 V³⁺ < V⁴⁺ by oxidation of V³⁺ to V⁴⁺ 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.

Fig. 2 Change in the hydrogen permeation flux through Pd-coating free V membrane with respect to time for 3 hours at 773 K under the hydrogen pressure difference of 0.1 MPa.