Sulfonated Poly(ether sulfone)-Coated and -Blended Nafion Membranes with Enhanced Conductivity and Reduced Hydrogen Permeability

Abstract

Nafion, as a perfluorosulfonic acid (PFSA)-based polymer, is a key material that contributes to the commercialization of proton exchange membrane fuel cells (PEMFCs). The high dependence on relative humidity (RH) of Nafion or other PFSA membranes for proton conduction, together with its decreased mechanical and dimensional stability and high fuel (H 2 ) crossover at the cell operating temperatures (80 °C or above), however, remain issues that have yet to be solved. In the current work, thin sulfonated poly(arylene ether sulfone) (sPES)-coated Nafion membranes (sPES-c-Nafions) are developed, for the first time, by simply spin-coating the sPES solution onto a Nafion membrane, and the results are compared with the sPES-blended Nafion counterparts. The sPES-c1-Nafion demonstrates a very high proton conductivity of 223.3 mS cm −1 (80 °C) and a very low hydrogen permeability, a 41% reduction compared to that of Nafion-212, together with improved mechanical and dimensional stabilities compared to Nafion-212. The developed membrane also shows excellent cell performance (i.e., with a current density of 1.56 A cm −2 and a peak power density of 1.20 W cm −2 at 0.6 V potential in the actual operating conditions of PEMFCs).

Nafion-Based Proton-Exchange Membranes Built on Cross-Linked Semi-Interpenetrating Polymer Networks between Poly(acrylic acid) and Poly(vinyl alcohol)

“…Also, the fuel cell performances of the semi-IPN composite membrane (NPP-95) and the re-Nafion membrane developed in this study were compared with those of the Nafion-based semi-IPN composite membranes used for PEMFC reported elsewhere (Figure S12). ,,− ,,,− It was found that the PEMFC performance of our semi-IPN membranes based on cross-linked PAA–PVA and Nafion was significantly higher than that of most other Nafion-based semi-IPN composite membranes. This result strongly indicates that our NPP-95 membrane has high practical PEMFC applications.…”

“…The amount of hydrogen permeated through membranes can be measured by counting the number of these ejected electrons. 46,53 The results showed that the hydrogen permeability of NPP-95 was significantly lower at 0.62 mA/cm 2 than that of re-Nafion at 1.46 mA/cm 2 . These results were consistent with the hydrogen permeability test results described earlier indicating that the semi-IPN membrane was highly effective at suppressing hydrogen crossover even under actual fuel cell operating conditions.…”

“…The water absorbed by PEMs can be largely divided into bound water and free water depending on the ability to interact with ion-conducting groups. Free water does not interact with ion-conducting groups, while bound water engages in strong interactions with ion-conducting groups. , Unlike water electrolyzers, which operate in water, fuel cell systems are designed to operate under 90–95% RH conditions (room humidity). Thus, the water necessary for ion conduction is fed in a humidified state.…”

“…To be more specific, the permeated hydrogen tends to be oxidized on the surface of the cathode catalyst (Pt); applying a linear sweep in voltage causes electrons to be ejected. The amount of hydrogen permeated through membranes can be measured by counting the number of these ejected electrons. , …”

A facile strategy to construct layered membranes with high and stable proton conductivity based on sulfonated graphene oxide

“…Relative to Nafion-112, the sPES-Nafion membrane exhibited a high proton conductivity, a low hydrogen permeability, and improved mechanical and dimensional stabilities. 19 Furthermore, the membranes with multilayered structure have been constructed through the alternate deposition of components by spin coating method. 20,21 In our previous study, the proton conductivity of PA doped membranes based on polyvinylidene fluoride (PVDF) reached 7.70 Â 10 À2 S/cm at 160 C. 21 However, there was a concern of performance degradation due to PA molecules leakage after a longterm operation in consideration of the lack of strong containers to anchor PA molecules.…”