(774a) Development of Proton Selective Membranes for Efficient and Economical Vanadium Redox Flow Batteries

Justin Walls, Padram Jahanian, Guangzhao Mao, Steven Salley, K. Y. Simon Ng

Department of chemical Engineering and Materials Science, College of Engineering,

Wayne State University, Detroit MI 48202

Flow Redox Batteries (FRBs), especially the Vanadium Redox Flow Battery (VRFB), provide a promising chemistry for storing intermittent renewable energy on a very large scale. While these batteries have already been developed on the megawatt hour level; none of the FRB technologies has seen significant market penetration. This is mainly because the technology is still very expensive, due to high material costs, and less than satisfactory performance parameters and reliability.

The key component of the VRFB, which is one of the leading causes of the elevated cost and unreliability, is the ion exchange membrane (IEM). The membranes need to possess good ion conductivity while maintaining high mechanical and chemical stability. Perfluorosulfonic polymers such as Nafion are the most common membranes for proton exchange in the VRFB due to their good chemical stability and high proton conductivity. However, due to the tendency of vanadium to pass through the membrane, Nafion membranes suffer from decreased energy efficiency. This project is focused on decreasing the vanadium ion diffusion through the membrane by modifying the nanostructure of Nafion. There has been extensive research activity in the modification of Nafion membranes, for example, modification by layer-by-layer polyelectrolyte multilayer films and in situ sol-gel reaction to close the pores by silica nano particles. Our project combines these two methods using hyper-branched polyelectrolyte multilayer films to further lower the vanadium ion diffusion rate.  Nafion modification by the sol-gel chemistry was conducted by treating the Nafion in the tetraethylorthosilicate (TEOS) methanol solution. Poly(diallyldimethylammonium chloride) (PDDA) and poly(sodium styrene sulfonate) was used in the layer-by-layer deposition. Diffusivity and ion crossover of these membranes was tested and compared to that of the unmodified membranes as well as other modification techniques that have been reported. A small scale VRFB system was constructed to test the performance of these modified membranes, and efficiency and reliability of the system as a whole was measured.