Influence of Ionomer Content in the Catalytic Layer of MEAs Based on Aquivion® Ionomer

Perfluorinated sulfonic acid (PFSA) polymers such as Nafion® are widely used for both electrolyte membranes and ionomers in the catalytic layer of membrane-electrode assemblies (MEAs) because of their high protonic conductivity, σH, as well as chemical and thermal stability. The use of PFSA polymers with shorter side chains and lower equivalent weight (EW) than Nafion®, such as Aquivion® PFSA ionomers, is a valid approach to improve fuel cell performance and stability under drastic operative conditions such as those related to automotive applications. In this context, it is necessary to optimize the composition of the catalytic ink, according to the different ionomer characteristics. In this work, the influence of the ionomer amount in the catalytic layer was studied, considering the dispersing agent used to prepare the electrode (water or ethanol). Electrochemical studies were carried out in a single cell in the presence of H2-air, at intermediate temperatures (80–95 °C), low pressure, and reduced humidity (50% RH. %). The best fuel cell performance was found for 26 wt.% Aquivion® at the electrodes using ethanol for the ink preparation, associated to a maximum catalyst utilization.

Purification of Wet-Process Phosphoric Acid via Donnan Dialysis with a Perfluorinated Sulfonic Acid Cation-Exchange Membrane

This work reports the application of an electromembrane process, Donnan dialysis (DD), for the purification of so-called wet-process phosphoric acid (WPA). Nitric acid is used as the stripping solution to remove metallic cations (mostly Fe3+, Al3+, and Mg2+) that are harmful to the further processing of WPA. The paper first presents a set of experimental data on the measurements of the metallic cation fluxes through a perfluorinated sulfonic acid cation-exchange membrane. Not only WPA, but also synthetic phosphoric acid solutions with mixed metallic cations (MPA) and with a single metallic cation (SPA) were studied. This confrontation confirms (1) that the order of metallic cations fluxes is Mg2+ > Al3+ > Fe3+; (2) that, compared with MPA, the purification effect of WPA causes only negligible change; (3) that, by comparing the DD processes with SPA and MPA solutions, the reason for the low transmembrane fluxes of Fe3+ and Al3+ could be explained by the large ionic charge and large hydrated ion radius. Furthermore, by analyzing the ion composition of membranes equilibrated in SPA solutions, we conclude that the forms of cations in the membrane are most likely Fe3+, Al3+, and Mg2+.

Impacts of Organic Sorbates on Ionic Conductivity and Nanostructure of Perfluorinated Sulfonic-Acid Ionomers

<p>This study provides insights into structure-property relationships of Nafion membranes swollen with organic sorbates, revealing correlations between sorbate polarity, ionomer domain structure, and ionic conductivity. Swelling, nanostructure, and ionic conductivity of Nafion in the presence of short-chain alcohols and alkanes was studied by infrared spectroscopy, X-ray scattering, and voltammetry. Nafion equilibrated with alkanes exhibited negligible uptake and nanoswelling, while alcohols induced nanoscopic- to macroscopic- swelling ratios that increased with alcohol polarity. In mixed-sorbate environments including organics and water, alcohols preserved the overall ionomer domain structure but altered the matrix to enable higher sorbate uptake. Alkanes did not demonstrably alter the hydrated nanostructure or conductivity. Identifying the impacts of organic sorbates on structure-property relationships in ionomers such as Nafion is imperative as membrane-based electrochemical devices find applications in emerging areas ranging from organic fuel cells to the synthesis of fuels and chemicals.</p>

Impacts of Organic Sorbates on Ionic Conductivity and Nanostructure of Perfluorinated Sulfonic-Acid Ionomers

<p>This study provides insights into structure-property relationships of Nafion membranes swollen with organic sorbates, revealing correlations between sorbate polarity, ionomer domain structure, and ionic conductivity. Swelling, nanostructure, and ionic conductivity of Nafion in the presence of short-chain alcohols and alkanes was studied by infrared spectroscopy, X-ray scattering, and voltammetry. Nafion equilibrated with alkanes exhibited negligible uptake and nanoswelling, while alcohols induced nanoscopic- to macroscopic- swelling ratios that increased with alcohol polarity. In mixed-sorbate environments including organics and water, alcohols preserved the overall ionomer domain structure but altered the matrix to enable higher sorbate uptake. Alkanes did not demonstrably alter the hydrated nanostructure or conductivity. Identifying the impacts of organic sorbates on structure-property relationships in ionomers such as Nafion is imperative as membrane-based electrochemical devices find applications in emerging areas ranging from organic fuel cells to the synthesis of fuels and chemicals.</p>