Warren, James Raphael (2012)
M.Res. thesis, University of Birmingham.
The use of high purity hydrogen (>99.9999%), refined by palladium based membranes, is critical to the lifetime of PEM fuel cells. The alloy currently used for purification is palladium-silver; which suffers from both low strength and poor resistance to poisoning. Palladium-copper may be a suitable alternative as it has reasonable permeability, particularly at 47 atomic% Pd. The Pd-Cu binary phase system has been studied although around the high permeability region the boundary lines remain unclear. A shift in the observed phase boundary line under hydrogen pressure is noted in the literature although little work to comprehensively study the extent of this effect has been carried out. Variations between the solubility and diffusivity of f.c.c. and b.c.c. grains may also have an effect on the thermal cycling properties of the alloy; potentially reducing membrane selectivity over time. Varying hydrogen content across the membrane is thought to give a structural gradient which could strongly affect the material properties and the optimum operating conditions. In this thesis in-situ XRD and permeability measurements of three Pd-Cu alloys have been performed to investigate the effect that hydrogen overpressure has on the observed phase boundary and optimisation of the membrane operating conditions for permeability.
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