Proton-exchange-membrane (PEM)-based devices are promising technologies for hydrogen production and electricity generation. Currently, the amount of expensive platinum catalyst used in these devices must be reduced to be cost-competitive with other technologies. These devices typically contain Nafion ionomer thin films in the catalyst layers, which are responsible for transporting protons and gaseous species to and from electrochemically active sites. The morphology of the Nafion ionomer thin films in the catalyst layers with reduced platinum loading is impacted by interactions with the catalyst and the confinement to nanometer thicknesses, which leads to performance losses in PEM-based devices. In this study, an elastin-like polypeptide (ELP) is designed to modulate the morphology of Nafion ionomer on platinum surfaces. The ELP shows an ability to assemble into a monolayer on platinum and change the ionomer interaction with platinum, thereby modifying its thin-film structure and improving the Nafion ionomer coverage. As a proof of concept, an ELP-modified catalyst ink was prepared and morphological differences were observed. Overall, we discovered an engineered ELP that can modulate the ionomer–catalyst interface in the electrodes of PEM-based devices.

Ionomer binders are critical materials for delivering ions to and from electrocatalyst surfaces in fuel cell and water electrolyzer technologies. Most studies examine these materials as bulk polymer electrolyte membranes, and comparatively little attention has been given to their behavior on electrode surfaces as thin films. This report demonstrates that sequence-defined peptides anchored to electrode surfaces, or the solvent vapor annealing processing, alters the microstructure configuration of anion exchange ionomers (AEIs). It is observed that moderately sized microphase-separated ionic domains of the AEI, obtained either by peptide-modified electrodes or solvent vapor annealing, give rise to a two- to three-fold increase in thin-film in-plane ionic conductivity. Interestingly, the use of peptide-modified electrodes, in conjunction with solvent vapor annealing, yields excessively large ionic grains that compromise ionic conductivity. Overall, the judicious use of sequence-defined peptides adsorbed to electrode surfaces, or solvent vapor annealing, encourage the appropriate microstructures of thin-film AEIs resulting in ameliorated ionic conductivity.

Commercial proton exchange membrane heavy-duty fuel cell vehicles will require a five-fold increase in durability compared to current state-of-the art light-duty fuel cell vehicles. We describe a new composite membrane that incorporates silicotungstic heteroply acid (HPA), α-K8SiW11O40▪13H2O, a radical decomposition catalyst and when acid-exchanged can potentially conduct protons. The HPA was covalently bound to a terpolymer of tetrafluoroethylene, vinylidene fluoride, and sulfonyl fluoride containing monomer (1,1,2,2,3,3,4,4-octafluoro-4-((1,2,2-trifluorovinyl)oxy)butane-1-sulfonyl fluoride) by dehydrofluorination followed by addition of diethyl (4-hydroxyphenyl) phosphonate, giving a perfluorosulfonic acid-vinylidene fluoride-heteropoly acid (PFSA-VDF-HPA). A composite membrane was fabricated using a blend of the PFSA-VDF-HPA and the 800EW 3M perfluoro sulfonic acid polymer. The bottom liner-side of the membrane tended to have a higher proportion of HPA moieties compared to the air-side as gravity caused the higher mass density PFSA-VDF-HPA to settle. The composite membrane was shown to have less swelling, more hydrophobic properties, and higher crystallinity than the pure PFSA membrane. The proton conductivity of the membrane was 0.130 ± 0.03 S/cm at 80˚C and 95% RH. Impressively, when the membrane with HPA-rich side was facing the anode, the membrane survived more than 800 h under accelerated stress test conditions of open-circuit voltage, 90˚C and 30% RH.

Chemical degradation and mechanical degradation are the major challenges for heavy-duty vehicle fuel cell commercialization. Perfluorinated sulfonic acid is the benchmark material that has high proton conductivity and robust mechanical properties. However, chemical degradation can occur through radical formation during the fuel cell operation. Chemical degradation can also have a synergetic effect with mechanical degradation. Recent studies have used cerium and manganese additives to suppress the radical formation or chemical degradation caused by radicals. The limitation of the metal and metal oxide additives was the migration and agglomeration of the additives. Both migration and clustering can lead to changes in membrane morphology, resulting in a loss in proton conductivity. Our group has previously reported that immobilization of heteropoly acid to a fluoroelastomer can be used to both enhance proton conductivity and chemical degradation. The durability test has shown that the chemical durability was significantly enhanced, but the mechanical durability remained the challenge. In this study, we hypothesized that when a heteropoly acid can be chemically bound to the perfluorinated polymer and cast on a composite membrane with expanded polytetrafluoroethylene (e-PTFE) will enhance the chemical and mechanical durability without migration. Proton conductivity was measured using impedance spectroscopy. The structure-property relationship was studied using multi-scale morphology analysis methods such as scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and small-angle x-ray scattering (SAXS). The chemical degradation will be tested under the highly accelerated standard test (HAST) condition, a more severe fuel cell operation condition than the accelerated standard condition (AST). The mechanical durability of the composite membrane will also be tested on the HAST condition with humidity cycling.