Hydrogen solubility and permeability of V–W–Mo alloy membrane for hydrogen separation and purification

The alloying effects of molybdenum (Mo) into V–W alloy on the solubility of hydrogen, the resistance to hydrogen embrittlement and the hydrogen permeability are investigated in a fundamental manner. It is found that the addition of Mo into V–W alloy decreases the hydrogen solubility. As a result, the applicable hydrogen pressures at the DBTC (the ductile-to-brittle transition hydrogen concentration, which is about 0.2 (H/M) for vanadium alloys) increases. In fact, about 0.15 MPa (673 K) to 0.6 MPa (773 K) of hydrogen pressures can be applied to V–5 mol%W–5 mol%Mo alloy membrane while keeping the hydrogen concentration less than or equal to the DBTC, which is about twice of hydrogen pressure applicable to V–5 mol%W alloy. Thus, the addition of Mo into V–W alloy improves the resistance to hydrogen embrittlement. In addition, the alloying of Mo into V–W alloy also improves the hydrogen permeability. For instance, the hydrogen permeability of V–5 mol%W–5 mol%Mo alloy is about 4–5 times higher than that of Pd–25mass%Ag alloy at 673–773 K.

• The concept for alloy design of Nb-based hydrogen permeable membrane is applied to V-based alloy.
• The addition of Mo into V–W alloy improves the resistance to hydrogen embrittlement.
• V–5 mol%W–5 mol%Mo alloy membrane exhibits excellent hydrogen permeability at 673–773 K.