Hydrogen (H2) and fuel cells applications are central to the realization of a global hydrogen economy. In this scenario, H2 may be produced from renewable biofuels via steam reforming and by solar powered water electrolysis. The purification required for fuel cell grade H2, whether in tandem or in situ within a catalytic reformer operating at 500 oC or above, would be greatly facilitated by the availability a cheaper and more robust option to palladium (Pd) dense metal membrane, currently the leading candidate. Here we describe our results on the feasibility of a completely novel membrane for hydrogen separation: Sandwiched Liquid Metal Membrane, or SLiMM, comprising of a low-melting, non-precious metal (e.g., Sn, In, Ga) film held between two porous substrates. Gallium was selected for this feasibility study to prove of the concept of SLiMM. It is molten at essentially room temperature, is non-toxic, and is much cheaper and more abundant than Pd. Our experimental and theoretical results indicate that the Ga SLiMM at 500 oC has a permeability 35 times higher than Pd, and substantially exceeds the 2015 DOE target for dense metal membranes. For developing a fundamental understanding of the thermodynamics and transport in liquid metals, a Pauling Bond Valence-Modified Morse Potential (PBV-MMP) model was developed. Based on little input, the PBV-MPP model accurately predicts liquid metal self-diffusion, viscosity, surface tension, as well as thermodynamic and energetic properties of hydrogen solution and diffusion in a liquid metal such as heat of dissociative adsorption, heat of solution, and activation energy of diffusion. The concept of SLiMM proved here opens up avenues for development practical H2 membranes, For this, improving the physical stability of the membrane is a key goal. Consequently, a thermodynamic theory was developed to better understand the change in liquid metal surface tension and contact angle as a function of temperature, pressure and gas-phase composition.
Worcester Polytechnic Institute
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Yen, P. (2016). Supported Liquid Metal Membranes for Hydrogen Separation. Retrieved from https://digitalcommons.wpi.edu/etd-dissertations/480
hydrogen separation, UBI-QEP, wettability, liquid metal
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