Numerical Simulation Of Ion Transport In Flow Battery Membranes With Aqueous Phase Structure

The ion exchange membrane which used in flow battery must be in good hydration status that can achieve good ion transmission and anti-pollution. The structural properties of nafion can be shown through the molecular dynamics simulations in different water content states. The simulations clearly show that the polymer consists of hydrophilic regions keeping water gathered and segregated hydrophobic regions which follow the polymer backbone. The size of water cluster completely depends on the water content. The water cluster just exists in tiny form in low water content level. As the water content increases, it will become a completed cluster in hydrophobic regions, and in addition, a continuous water channel will be formed with these clusters connecting to each other. The relation between each atomic can be shown by the radial distribution function. As the water content increases, the hydronium ions will become hydrated increasingly. It is possible in the form of Eigen ions after hydrating. These simulations testified that the conductivity of these membranes was very poor in low water contents. Because there was no connection between each cluster, the size of clusters was small, and there was no channel construction forming caused the poor conductivity.When the side-chain is different, compared the nafion, aciplex, dow and flemion. Analysis the structural properties of water cluster and network ion transmission channel around polymer backbone and side-chain after simulations. The water cluster are composed of hydrated hydrogen ions and water molecular. We found that ion transmission property completely depends on water content. The most effective structure is side-chain length for ion transmission. The side-chain length of nafion is intermediate among the four polymers. Through the simulations also confirmed that nafion structure is the most reasonable. It is the model of perfluorinated acid membrane.Study the performances and the relative humidity affection in the ion transport of nation and the sulfonated polyether sulfone membrane through molecular dynamics simulation. There are three forms of recent proposed sulfonated polyether sulfone membrane. Defineλas the ratio of number of water molecular to number of sulfonic acid group. We analyzed the structural properties of water molecules and sulfonate through the radial distribution function whenλare equal. We found that there was no water cluster around sulfonate of sulfonated polyether sulfone membrane whenλis small or the cluster is too little. There is no continuous channel formed which convenient to ion transport for no connection to each other.