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Abstract:
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With its long cycle life and scalable design , the vanadium redox flow battery (VRB ) is a promising technology for grid energy storage . However , high materials costs have impeded its commercialization . An essential but costly component of the VRB is the ion -exchange membrane . The ideal VRB membrane provides a highly conductive path for protons , prevents crossover of reactive species , and is tolerant of the acidic and oxidizing chemical environment of the cell . In order to study membrane performance and optimize cell design , mathematical models of the separator membrane have been developed . Where previous VRB membrane models considered minimal details of membrane transport , generally focusing on conductivity or self -discharge at zero current , the model presented here considers coupled interactions between each of the major species by way of rigorous material balances and concentrated solution theory . The model describes uptake and transport of sulfuric acid , water , and vanadium ions in Nafion membranes , focusing on operation at high current density . Governing equations for membrane transport are solved in finite difference form using the Newton -Raphson method . Model capabilities were explored , leading to predictions of Ohmic losses , vanadium crossover , and electro -osmotic drag . Experimental methods were presented for validating the model and for further improving estimates of uptake parameters and transport coefficients . |