Abstract
Commercial Nafion membranes have been widely used for vanadium redox flow batteries (VRFB) but with relatively low ion selectivity. A chemical method is commonly employed to modify the organic membranes, whereas physical approaches are rarely reported in view of less compatibility with the organic species. In this study, an ultrathin polytetrafluoroethylene (PTFE) film of less than 30 nm is deposited onto the Nafion substrates by radio frequency magnetron sputtering to form PTFE@Nafion composite membranes. The PTFE layer of hydrophobic and inert feature enhances the dimensional stability and the ion selectivity of the Nafion membranes. The VRFB single cell with an optimized composite membrane exhibits a better self-discharge property than that of the Nafion 212 (i.e., 201.2 vs. 18.6 h), due to a higher ion selectivity (i.e., 21.191 × 104 vs. 11.054 × 104 S min cm–3). The composite membranes also show better discharge capacity retention than the Nafion 212 over the entire 100 cycles. The results indicate that the magnetron sputtering is an alternative and feasible route to tailor the organic membranes via surface modification and functionalization.
Highlights
The utilization of renewable energies has been the global focus towards sustainable development [1–5]
Once formed on the Nafion surface, it behaves as a blocking layer to expel the water molecules and retard the ion permeation
This is attributed to an enhanced energy of Ar+ ions that generate more PTFE particles with a high deposition rate
Summary
The utilization of renewable energies (e.g., wind, solar, and tidal energy) has been the global focus towards sustainable development [1–5]. To reduce ion permeability and enhance ion selectivity, chemical strategies have been the prevailing approach to modify and improve the Nafion-based membranes, such as sol–gel modification, interfacial polymerization, oxidation polymerization, surfactant treatment, solution casting, and electrodeposition. The pores of Nafion membrane were filled with the SiO2 nanoparticles, resulting in reduced permeability of vanadium ions Polymerization is another useful method to introduce organic species. It is noteworthy that the chemical methods usually require harsh environments and multiple reactions with delicate conditions To this end, a physical deposition approach is an alternative which is, rarely reported due to less compatibility with the organic species. An ultrathin PTFE layer is deposited onto the Nafion surface and performs as a blocking layer to reduce the permeation of vanadium ions and enhance the dimensional stability of the Nafion membranes for VRFB application
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