Tuning the microstructure and hydrogen permeability of VC/V composite membranes by radio frequency magnetron sputtering with applied substrate bias

Abstract

Our recent work has shown that vanadium carbide (VC) films prepared by radio frequency magnetron sputtering (RFMS) can be used as H2 dissociation/recombination catalysts on vanadium (V) for high temperature hydrogen separation. During the deposition of VC on V by RFMS, substrate bias was further applied to tune the microstructure and hydrogen permeability of the VC/V composite membranes. It is found that moderate substrate bias during RFMS generates nanocrystalline VC films with hexagonal close packed V2C (hcp-V2C) phase, which exhibits finer grain size and higher carbon vacancy density compared to the films with face centered cubic VC (fcc-VC) phase prepared by RFMS without bias. The increase in carbon vacancy density results in an increase in the electron density around the Fermi level (EF) and a lowering of the d-band center for the VC, which contributes to its catalytic activity. The resulted VC/V composite membranes show significantly enhanced hydrogen permeability, particularly at all temperatures evaluated, above that of industrially used Pd. This work demonstrates that RFMS with applied substrate bias as microstructural engineering is an efficient method to prepare highly hydrogen-permeable VC/V composite membranes.