Alkaline anion-conducting polymer-based CO2 electrolysis and water electrolysis are among two emerging renewable energy conversion technologies. Their system design and integration offer promise of lower capital cost due to utilization of low-cost catalysts, in contrast to platinum group metal catalysts required for cation-conducting polymer-based devices. However, a critical component, the polymer electrolyte membrane, remains an obstacle hampering system performance and durability. In this study, commercially-available Sustainion® membranes with and without PTFE-reinforcement were investigated to understand previously unreported origins of improved device performance when compared to alternative membrane chemistries. We report critical membrane properties, such as morphology, thermal stability, as well as temperature-, hydration-, and counter-ion dependent ion conductivity. Moveover, the changes in uptake and conductivity of membranes in supporting electrolytes of K2CO3 and KOH investigated as a function of their concentration. Presence of reinforcement and supporting electrolyte type alter the membrane's transport functionality, which could help guide device design for improved performance. The obtained results not only show how Sustainion® properties change with operating environment for CO2 and water electrolysis applications, but also provide understanding for internal and external factors controlling anion-exhcnage membrane functionality in electrochemical devices.

Hydroxide-exchange membrane (HEM) fuel cells are emerging energy conversion technologies. A significant effort has been expended to develop new HEMs with enhanced transport functionality, which has driven the need for understanding how transport of hydroxide and other anions in these membranes is related to hydration and nano-morphology. In this work, we report the results of a systematic study on poly(aryl piperidinium)-based on terphenyl (PAP-TP-85), a HEM that previously showed promising fuel cell performance and durability. Membrane water uptake and anion conductivity in liquid and vapor water, as well as the impact of counter-anion forms on these properties, are investigated and compared with a commercial anion exchange membrane (AEM), Fumasep FAA3, and proton-exchange membranes (PEMs), Nafion and sPEEK. Different water uptake in liquid vs. saturated vapor is observed for both AEMs (i.e., PAP and FAA3), indicating Schroeder's paradox, regardless of anion form. Morphology of AEMs examined via small-angle X-ray scattering (SAXS) shows weak phase-separation, regardless of hydration level and anion type, which is attributed to the reduced chemical dissimilarity between the backbone and ionic moieties. Despite both AEMs' amorphous nanostructure, PAP-AEM has a higher ion conductivity than FAA3. Water content plays a more significant role than does temperature in controlling the anion conductivity in water vapor. In liquid water, normalized conductivity shows a universal dependence on hydration, regardless of the anion form. Moreover, in water vapor, conductivity is influenced more by ion mobility than ion concentration, and depends mainly on hydration. Thus, ion transport in disordered AEMs is governed primarily by hydration, in contrast to phase-separated ionomers, where ion transport is governed by nanostructure-hydration interplay. This study demonstrates the importance of hydration level and ion mobility for anion transport in amorphous AEMs and provides an understanding of parameters governing their transport properties.

Polymer-electrolyte membrane (PEM) fuel-cells are one of the most promising energy conversion technologies for renewable clean energy applications. A major challenge preventing the widespread use and commercialization of PEM fuel cells is achieving high performance with low-loadings of platinum group metal (PGM) catalysts. One of the factors driving performance limitations in the cell is the mass transport losses within the cathode catalyst layers (CCL) due to sluggish oxygen-reduction reactions occurring at the platinum-ionomer interface. Any resistance to transport of these ionic and gaseous species within the CCL results in mass-transport limitations and performance losses, especially at high current densities. It is known that mass-transport losses increase with reduced platinum loading, thereby creating a performance-cost tradeoff for fuel cells. A viable solution to reduce the transport resistances in the catalyst layers is to create new ionomers that can provide good ion and oxygen transport needed to accomplish high-performing fuel cell catalysts. Using this approach Tetramer Technologies and LBNL propose improved fuel-cell catalyst ionomers based on Tetramers proprietary polymer chemistry.

Ionomer thin-films (i.e., 20–100 nm) on supports serve as model systems to understand ionomer-catalyst interfacial behavior as well as the confinement-driven deviation in properties from bulk membranes. While ionomer thin-films have been examined for proton exchange ionomers, the thin-film properties of anion exchange ionomers (AEIs) remain largely unexplored. More importantly, delineating the convoluted impact of chemistry and confinement on thin-film morphology and hydration is of interest to advancing the field on functional ionic interfaces. In this work, these aspects are studied by using AEIs of different backbones (perfluorinated, aliphatic, and aromatic) and side chains (various lengths, and single versus dual functional groups). Quartz-crystal microbalance and spectroscopic ellipsometry are used to analyze density and coupled with calculated free volume fraction of thin-films to provide insights on their gas transport properties. AEI side-chain's chemical character plays a key role in how confinement modulates hydration (in thin-film versus bulk). The results elucidate the effects of backbone, side-chain chemistry versus anion/cation type in the confinement-driven changes in thin-film morphology and swelling. This study also provides new insights for tuning AEI transport functionalities at interfaces via chemistry, which can benefit the design and development of electrode-ionomers for alkaline membrane-based energy systems.

Electrochemical carbon dioxide reduction (CO2R) provides a promising pathway for sustainable generation of fuels and chemicals. Copper (Cu) electrocatalysts catalyse CO2R to valuable multicarbon (C2+) products, but their selectivity depends on the local microenvironment near the catalyst surface. Here we systematically explore and optimize this microenvironment using bilayer cation- and anion-conducting ionomer coatings to control the local pH (via Donnan exclusion) and CO2/H2O ratio (via ionomer properties), respectively. When this tailored microenvironment is coupled with pulsed electrolysis, further enhancements in the local ratio of CO2/H2O and pH are achieved, leading to selective C2+ production, which increases by 250% (with 90% Faradaic efficiency and only 4% H2) compared with static electrolysis over bare Cu. These results underscore the importance of tailoring the catalyst microenvironment as a means of improving overall performance in electrochemical syntheses.

Polymer-electrolyte membranes (PEMs) are a key component in electrochemical energy conversion devices where their main function is to selectively transport ionic species. Reducing PEM thickness is an effective strategy for improving performance by minimizing transport losses. However, how thickness affects the intrinsic properties of a membrane remains unexplored. This work aims to understand the effect of membrane thickness on structure-property relationships of 3 M perfluorosulfonic acid (PFSA) ionomer. We carried out a systematic investigation of membranes in a thickness range of 5-70 μm to examine their hydration behavior, morphology, crystallinity, mechanical properties, and gas and proton transport, with a discussion on the effect of thermal treatments. The collected dataset demonstrates PFSA membranes exhibit transitions in certain structural features below 10 μm, accompanied by an increased anisotropy in swelling and conductivity. Many properties deviate within 10%-20% without monotonic changes with thickness, however, linear correlations are observed between thickness and thermal-mechanical properties and gas permeability, although the latter is less significant. Identifying the thickness-dependence of PFSA properties could help expand the parameter window of PEMs, thereby enabling their optimization for automotive fuel cells, heavy-duty applications, and electrolyzers, especially if the membrane thickness is considered as part of dispersion-casting and reinforcement strategies.

In the version of this Article initially published, processing errors affected the graphics in Figs. 3 and 5. In Fig. 3e,f, the two center column x-axis labels inadvertently duplicated Fig. 2e,f labels. The labels have been corrected to read “Naf850 /Cu with Li+” and “Naf1100 /Cu with Li+” from left to right, for Fig. 3e and Fig. 3f. In Fig. 5, arrow tails have been restored to the seven arrowheads at top and bottom of the figure, while in Fig. 5c, “OH–” has been repositioned next to “CEI changes local.” The changes have been made to the online version of the Article.

Perfluorosulfonic acids (PFSAs) are commonly used as solid polymer electrolyte membranes (PEMs) in electrochemical energy devices, where they are vulnerable to attack by radical species during operation. A popular strategy to combat this problem is to introduce radical scavengers like cerium (Ce) ions that neutralize these species before they attack the PFSA. Such cation doping creates a multi-ion system, in which understanding the mechanisms of cation solvation and transport becomes important for the effective design and utilization of PFSA-cation systems. Ce ions also provide a representative model system for multication-exchanged ionomers in electrochemical systems. In this study, hydration and conductivity measurements, along with X-ray fluorescence and scattering, are employed to elucidate how Ce ion exchange alters PFSA's ionic solvation, as well as nano- and mesoscale morphologies, which ultimately control its ion transport properties. A molecular transport model is used to deconvolute the impact of Ce ions on the local solvation structure of water in the membrane from mesoscale changes of the transport pathways. The combined experimental and theoretical analysis reveals a nonlinear decrease in conductivity driven by cation solvation at the molecular level and morphological changes at longer length scales. Migration-diffusion coupling, its nonlinear dependence on ion exchange and hydration, and its overall implications for ionomer performance are also discussed. These findings have the potential to be translated into other mixed cation-ionomer systems for a wide range of energy and environmental devices.

Primary open-angle glaucoma is the most common optic neuropathy and an important cause of irreversible blindness worldwide. The optic nerve head or optic disc is divided in two parts: a central cup (without nerve fibers) surrounded by the neuroretinal rim (containing axons of the retinal ganglion cells). The International Glaucoma Genetics Consortium conducted a meta-analysis of genome-wide association studies consisting of 17,248 individuals of European ancestry and 6,841 individuals of Asian ancestry. The outcomes of the genome-wide association studies were disc area and cup area. These specific measurements describe optic nerve morphology in another way than the vertical cup-disc ratio, which is a clinically used measurement, and may shed light on new glaucoma mechanisms. We identified 10 new loci associated with disc area (CDC42BPA, F5, DIRC3, RARB, ABI3BP, DCAF4L2, ELP4, TMTC2, NR2F2, and HORMAD2) and another 10 new loci associated with cup area (DHRS3, TRIB2, EFEMP1, FLNB, FAM101, DDHD1, ASB7, KPNB1, BCAS3, and TRIOBP). The new genes participate in a number of pathways and future work is likely to identify more functions related to the pathogenesis of glaucoma.

Glaucoma is characterized by irreversible optic nerve degeneration and is the most frequent cause of irreversible blindness worldwide. Here, the International Glaucoma Genetics Consortium conducts a meta-analysis of genome-wide association studies of vertical cup-disc ratio (VCDR), an important disease-related optic nerve parameter. In 21,094 individuals of European ancestry and 6,784 individuals of Asian ancestry, we identify 10 new loci associated with variation in VCDR. In a separate risk-score analysis of five case-control studies, Caucasians in the highest quintile have a 2.5-fold increased risk of primary open-angle glaucoma as compared with those in the lowest quintile. This study has more than doubled the known loci associated with optic disc cupping and will allow greater understanding of mechanisms involved in this common blinding condition.