The visible absorption band of iodine adsorbed on zeolite blue-shifted with increasing the electropositivity of the countercation and the aluminum content in the framework. This phenomenon was attributed to the increase in the donor strength of the zeolite framework based on the analogous spectral shift of iodine in solution. In support of this, a negative linear correlation was observed between the measured visible bands of iodine adsorbed on various zeolites and their calculated Sanderson's intermediate electronegativities. However, the simultaneous change in the electrostatic field strength within the zeolite pores, as a result of the change in the number and the size of the cation, has to be taken into account in order to interpret the overall spectral shifts more precisely. The iodine band sensitively blue-shifted with decreasing the moisture content in the framework but red-shifted with the loss of NH3 from NH4 +-exchanged zeolites. The visible band of iodine also progressively red-shifted with increasing the adsorbed amount, presumably due to the nature of iodine to deplete electron density from the framework. The framework structure also affected the spectral shift of the visible iodine band. The overall results established that iodine can be used as a novel molecular probe for the quantitative evaluation of the zeolite donor strength.

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Summary The physicochemical properties of perfluorinated sulfonic acid (PFSA) polymers are closely correlated with their nanostructure. However, their real nano‐structural morphology is still controversial because it is difficult to observe their accurate morphology at the nanoscale. Moreover, studies on the nanostructures of the PFSA membranes have been mainly focused on the ionic domain. On this basis, here we describe the crystalline domain of two PFSA membranes as well as their ionic domain based on small‐angle X‐ray scattering results. Both ionic and crystalline domains showed significant alterations during hydration, and the different behaviors based on the side‐chain length of the two PFSA membranes are also described. The short side chain‐tethered PFSA membrane (higher ion exchange capacity (IEC)) showed a widespread ionic domain and lacking crystalline domain with their relatively temperature‐dependent tendency compared to the flexible long side chain‐tethered PFSA membrane (lower IEC). On this basis, the correlation between nanostructure and membrane properties is described from various perspectives.

To greatly increase the proton conductivity of a sPEEK nanocomposite membrane without water swelling problems, sulfonated PEEK (sPEEK) nanocomposite membranes were prepared by regulating the nanocomposite concentration of sulfonated POSS (sPOSS). Incorporation of sPOSS into sPEEK afforded a 39% increase in proton conductivity at 80 °C/100% RH and a 70% increase in cell performance at 1.5 wt% sPOSS concentration. In particular, water swelling problems were not observed even with the attained proton conductivity, as with Nafion. The water swelling of the pristine sPEEK membrane was 18.8%; it increased to 24.4% at 5.0 wt% of sPOSS loading, which was 11.1% lower than that of Nafion. The high modulus of sPOSS and the good distribution of sPOSS also enhanced the tensile strength by 40.5% and the strain by 65.8% compared with the pristine sPEEK membrane. At more than 1.5 wt% sPOSS concentration, the conductivity and power output of the nanocomposite membranes decreased despite the increased IEC, which is highly related to aggregation of sPOSS nanoparticles in the proton conducting nanochannels and changes in the nanochannel size. The sizes of the nanochannels were measured by SAXS, and it was found that expansion of the nanochannels was enhanced at 1.5 wt% by the best distribution of sPOSS and absorption of water. The increased IEC, expanded nanochannels and distribution of sPOSS without aggregation promoted proton conduction through the nanochannels.

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High-performance electrochemical devices require a specific size of nanochannel in ion-exchange membranes for producing stable cell performance. We have tuned the size of the water nanochannel by varying the ion-exchange capacity of the membrane. It influences the current density of electrochemical devices. Here, we have demonstrated large-area dual-purpose membranes, implemented in reverse electrodialysis and fuel cell systems for generating power. The selectivity, compatibility, and flexibility of the membrane with the electrode are outstanding and have been explained in great detail. In this article, we have illustrated a novel combination of sPEEK/FAA-3 membranes for reverse electrodialysis applications as a cation and an anion. The membrane can freely withstand structural stability and durability at high temperatures under hydrated conditions and offers excellent results in the fuel cell. We achieve superior performance for both fuel cells and reverse electrodialysis cells without altering the device architecture. Membranes with varying ion-exchange capacity (IEC) values and their electrochemical applications at one platform contribute to paving the path for enhancing the device performance.

The metastable state of any solution is a key component for achieving well-distributed nanochannels in membrane technology. This state affects the robustness and performance of the membrane in the long run in electrochemical systems. Here, we describe a method for producing a stable colloidal solution of amorphous metal-free nanosheets for the preparation of hybrid membranes. We demonstrate that the colloidal suspension hardly affects the width of the nanochannel in the membrane under the hydrated condition. We further show that the scattering of light in a colloidal suspension provides insights into the interaction between the nanosheet and the ionomer. Under the hydrated condition, a significant increase in the diffusion coefficient with efficient radial distribution between two different particles is noticed. A stable suspension of amorphous 2D nanosheets in the ionomer solution not only avoids the deteriorating mechanical stability of the membrane but also acts as an active material for reducing fuel crossover in the electrochemical cell.