Abstract
Previous experiments of water vapor penetration into polyelectrolyte membrane (PEM) thin films have indicated the influence of the water concentration gradient and polymer chemistry on the interface evolution, which will eventually affect the efficiency of the fuel cell operation. Moreover, PEMs of different side chains have shown differences in water cluster structure and diffusion. The evolution of the interface between water and polyelectrolyte membranes (PEMs), which are used in fuel cells and flow batteries, of three different side-chain lengths has been studied using dissipative particle dynamics (DPD) simulations. Higher and faster water uptake is usually beneficial in the operation of fuel cells and flow batteries. The simulated water uptake increased with the increasing side chain length. In addition, the water uptake was rapid initially and slowed down afterwards, which is in agreement with the experimental observations. The water cluster formation rate was also found to increase with the increasing side-chain length, whereas the water cluster shapes were unaffected. Water diffusion in the membranes, which affects proton mobility in the PEMs, increased with the side-chain length at all distances from the interface. In conclusion, side-chain length was found to have a strong influence on the interface water structure and water penetration rates, which can be harnessed for the better design of PEMs. Since the PEM can undergo cycles of dehydration and rehydration, faster water uptake increases the efficiency of these devices. We show that the longer side chains with backbone structure similar to Nafion should be more suitable for fuel cell/flow battery usage.
Highlights
Polyelectrolyte membranes (PEMs) are widely used in fuel cells and flow batteries
Hsu, and other co-workers [1,2] suggested water attached to ionic groups, forming spherical clusters of 4 to 6 nm that are distributed in the hydrophobic phase
We can see that water is quite continuous near the initial interface at time step = 100,000
Summary
Polyelectrolyte membranes (PEMs) are widely used in fuel cells and flow batteries. They are used to provide a pathway for proton transport and separate gases/electrolytes from mixing. PEMs absorb water on contact, and connected water pathways are formed inside the PEM. Polyelectrolyte membranes have a variety of chemical structures. The most commonly used PEM is Nafion, which has a polytetrafluoroethylene (PTFE) hydrophobic backbone and a highly hydrophilic (due to the presence of a sulfonic acid group) side chain; see Figure 1b. A variety of models for the nanomorphology of Nafion have been proposed. Hsu, and other co-workers [1,2] suggested water attached to ionic groups, forming spherical clusters of 4 to 6 nm that are distributed in the hydrophobic phase
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
