Layer-structured hydrogen permeable membranes and their application in hydrogen membrane fuel cells

Abstract

• Significantly improved hydrogen permeability at low temperature. • Negative activation energy for hydrogen permeation due to the V/Nb mid-layer. • Superior hydrogen permeability over the permeability of PdAg 25 at 298K. • Low-temperature operation of hydrogen membrane fuel cells. V and Nb are hydrogen permeable metals exhibiting greater hydrogen purification ability than Pd, but the permeability is not high enough due to low hydrogen dissociation and surface oxidation. In this study, two types of non-Pd hydrogen permeable membranes with a triple layer structure, Ni 64 Zr 36 /V/Ni 64 Zr 36 and Ni 64 Zr 36 /Nb/Ni 64 Zr 36 , have been prepared to produce a stable membrane exhibiting superior hydrogen permeability at low temperature range near to room temperature. The triple layer consists of 10 to 100 nm - thick amorphous Ni 64 Zr 36 thin films deposited by magnetron sputtering onto the surfaces of each 25 μm - thick crystalline V and Nb membranes. Significantly high hydrogen permeability over that of PdAg 25 below 373 K was observed in the prepared membranes. The performance of the triple membranes and the effect of the Ni 64 Zr 36 coating thickness on its hydrogen permeability are reported. Low-temperature hydrogen membrane fuel cells (LT-HMFCs) are built using the composite electrolytes composed of the suggested triple membrane and a glass fiber layer with phosphoric acid. The Nb and V interlayer plays an important role in implementing LT-HMFCs by improving hydrogen solubility and increasing hydrogen permeability at low temperature through its intrinsic activation energy, which is inversely proportional to temperature. The maximum output power obtained from LT-HMFC with 50 nm - thick V mid layer was 0.98 mW/cm 2 , at 423 K.