As substantial progress has been made in improving the performance of anion exchange membrane fuel cells (AEMFCs) over the last decade, the durability of AEMFCs has become the most critical requirement to deploy competitive energy conversion systems. Because of different operating environments from proton exchange membrane fuel cells, several AEMFC-specific component degradations have been identified as the limiting factors influencing the AEMFC durability. In this article, AEMFC durability protocol, the current status of AEMFC durability, and performance degradation mechanisms are reported based on the discussion during the US Department of Energy (DOE) Anion Exchange Membrane Workshop at Dallas, Texas, May 2019. With additional recent progress, we provide our perspectives on current technical challenges and future action to develop long-lasting AEMFCs.

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Durability challenges of anion exchange membrane fuel cells

Alkaline anion exchange membrane (AEM) electrolysers to produce hydrogen from water are still at an early stage of development, and their performance is far lower than that of systems based on proton exchange membranes. Here, we report an ammonium-enriched anion exchange ionomer that improves the performance of an AEM electrolyser to levels approaching that of state-of-the-art proton exchange membrane electrolysers. Using rotating-disk electrode experiments, we show that a high pH (>13) in the electrode binder is the critical factor for improving the activity of the hydrogen- and oxygen-evolution reactions in AEM electrolysers. Based on this observation, we prepared and tested several quaternized polystyrene electrode binders in an AEM electrolyser. Using the binder with the highest ionic concentration and a NiFe oxygen evolution catalyst, we demonstrated performance of 2.7 A cm−2 at 1.8 V without a corrosive circulating alkaline solution. The limited durability of the AEM electrolyser remains a challenge to be addressed in the future. Anion exchange membrane water electrolysers have potential cost advantages over proton exchange membrane electrolysers, but their performance has lagged behind. Here the authors investigate the cause of the poor performance of anion exchange membrane electrolysers and design ionomers that can overcome some of the challenges.

https://www.nature.com/articles/s41560-020-0577-x.pdf?proof=t

Highly quaternized polystyrene ionomers for high performance anion exchange membrane water electrolysers

Molecular Design of Single-Atom Catalysts for Oxygen Reduction Reaction

Alkaline-Stable Anion Exchange Membranes: A Review of Synthetic Approaches

Herein we detail the development of a new high-density polyethylene-(HDPE)-based radiation-grafted anion-exchange membrane (RG-AEM) that achieves a surprisingly high peak power density and a low in situ degradation rate (with configurations tailored to each). We also show that this new AEM can be successfully paired with an exemplar non-Pt-group cathode.

/pdf/radiation-grafted-anion-exchange-membranes-the-switch-from-49bmvaikhm.pdf

Radiation-grafted anion-exchange membranes: the switch from low- to high-density polyethylene leads to remarkably enhanced fuel cell performance

One promising approach to reduce the cost of fuel cell systems is to develop hydroxide exchange membrane fuel cells (HEMFCs), which open up the possibility of platinum-group-metal-free catalysts and low-cost bipolar plates. However, scalable alkaline polyelectrolytes (hydroxide exchange membranes and hydroxide exchange ionomers), a key component of HEMFCs, with desired properties are currently unavailable, which presents a major barrier to the development of HEMFCs. Here we show hydroxide exchange membranes and hydroxide exchange ionomers based on poly(aryl piperidinium) (PAP) that simultaneously possess adequate ionic conductivity, chemical stability, mechanical robustness, gas separation and selective solubility. These properties originate from the combination of the piperidinium cation and the rigid ether-bond-free aryl backbone. A low-Pt membrane electrode assembly with a Ag-based cathode using PAP materials showed an excellent peak power density of 920 mW cm−2 and operated stably at a constant current density of 500 mA cm−2 for 300 h with H2/CO2-free air at 95 °C. A key challenge for hydroxide exchange membrane fuel cells is the development of membranes with both high ionic conductivity and mechanical strength. Here the authors report a high-performance family of poly(aryl piperidinium) membranes enabling promising durability and power density.

Poly(aryl piperidinium) membranes and ionomers for hydroxide exchange membrane fuel cells

Production of hydrocarbon-based, alkaline exchange, membrane-electrode assemblies (MEA's) for fuel cells and electrolyzers is examined via catalyst-coated membrane (CCM) and gas-diffusion electrode (GDE) fabrication routes. The inability effectively to hot-press hydrocarbon-based ion-exchange polymers (ionomers) risks performance limitations due to poor interfacial contact, especially between GDE and membrane. The addition of an ionomeric interlayer is shown greatly to improve the intimacy of contact between GDE and membrane, as determined by ex situ through-plane MEA impedance measurements, indicated by a strong decrease in the frequency of the high-frequency zero phase angle of the complex impedance, and confirmed in situ with device performance tests. The best interfacial contact is achieved with CCM's, with the contact impedance decreasing, and device performance increasing, in the order GDE >> GDE+Interlayer > CCM. The GDE+interlayer fabrication approach is further examined with respect to hydrogen crossover and alkaline membrane electrolyzer cell performance. An interlayer strongly reduces the rate of hydrogen crossover without strongly decreasing electrolyzer performance, while crosslinking the ionomeric layer further reduces the crossover rate though also limiting device performance. The approach can be applied and built upon to improve the design and production of alkaline, and more generally, hydrocarbon-based MEA's and exchange membrane devices.

Design Strategies for Alkaline Exchange Membrane–Electrode Assemblies: Optimization for Fuel Cells and Electrolyzers

A membrane for fuel cells, such as PEM and/or AEM fuel cells and/or electrolyzers is disclosed. Such a membrane (e.g., an anion conducting membrane) may include: crosslinked ionomer comprising two types of functional groups: a first type of functional groups forming crosslinking bonds between two ionomer chains; and a second type of functional groups comprising ion conducting functional groups. In some embodiments, the crosslinking bonds may not include the ion conducting functional groups. A catalyst coated membrane (CCM) is also disclosed. In such case the membrane may further include at least one catalyst layer attached to at least one side of the membrane to form the catalyst coated membrane (CCM). The at least one catalyst layer may include catalyst nanoparticles and crosslinked ionomer of the catalyst layer comprising two types of functional groups.

Alina Amel

Papers

Poly(aryl piperidinium) membranes and ionomers for hydroxide exchange membrane fuel cells

Design Strategies for Alkaline Exchange Membrane–Electrode Assemblies: Optimization for Fuel Cells and Electrolyzers

Membranes for fuels cells and method of making same