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.

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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

Here, we have developed a dissolved oxygen and galvanic corrosion method to synthesize vertically aligned fluoride-incorporated nickel–iron oxyhydroxide nanosheet arrays on a compressed Ni foam as ...

Water-Fed Hydroxide Exchange Membrane Electrolyzer Enabled by a Fluoride-Incorporated Nickel–Iron Oxyhydroxide Oxygen Evolution Electrode

Ion-exchange capacity (IEC) is the measure of a material’s capability to displace ions formerly incorporated within its structure. IEC is a key feature of anion-exchange membranes (AEM), as it determines the AEM’s ability to conduct the ions required to sustain the electrochemical reactions where they are utilized. As an intrinsic property, measuring the IEC accurately is essential to study AEMs and understand their performance within devices. In this method article, a facile and accurate standard operating procedure (SOP) to measure the IEC of AEMs is proposed. When compared to conventional acid-base back-titration or Mohr titration, the proposed method combines the fast reaction between silver and halide ions and the accuracy of the potentiometric titration, providing a convenient and precise protocol for researchers in the field.

/pdf/standard-operating-protocol-for-ion-exchange-capacity-of-3ka5fm7m.pdf

Standard Operating Protocol for Ion-Exchange Capacity of Anion Exchange Membranes

Sulfurized polyacrylonitrile (SPAN) cathodes have shown great prospects in commercial applications due to the high discharge capacity, good cycle stability, and low self-discharge rate. However, high sulfurization temperature results in loss of nitrogen atoms, which leads to imperfect SPAN structure and is not conducive to fast electron transfer. A high efficiency vulcanizing agent of S2Cl2 was used to reduce the reaction temperature in this work. We found that S2Cl2 promotes PAN cyclization, reduces the cyclization reaction temperature, and avoids the loss of nitrogen atoms and the agglomeration of SPAN primary particles in high-temperature reactions. The SPAN cathode material prepared using S2Cl2 has a more regular structure six-membered ring main chain structure and a smaller primary particle size, which is beneficial to the rapid conduction of electrons and lithium ions in the electrode material. The electrochemical test results confirmed that the SPAN cathode material prepared by S2Cl2 has higher active material utilization, better cycle stability, and better rate performance. 

Disulfide Dichloride: A High Efficiency Vulcanizing Agent for Sulfurized Polyacrylonitrile

SEBS block copolymers or norbornene-pyrrolidinium random or block copolymers with pendant cationic groups are provided which have an alkaline-stable cation introduced into a rigid aromatic polymer backbone free of ether bonds. Hydroxide exchange membranes or hydroxide exchange ionomers formed from these polymers exhibit superior chemical stability, hydroxide conductivity, decreased water uptake, good solubility in selected solvents, and improved mechanical properties in an ambient dry state as compared to conventional hydroxide exchange membranes or ionomers. Hydroxide exchange membrane fuel cells comprising the SEBS block copolymers or norbornene-pyrrolidinium random or block copolymers with pendant cationic groups exhibit enhanced performance and durability at relatively high temperatures.

Lan Wang

Papers

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

Water-Fed Hydroxide Exchange Membrane Electrolyzer Enabled by a Fluoride-Incorporated Nickel–Iron Oxyhydroxide Oxygen Evolution Electrode

Standard Operating Protocol for Ion-Exchange Capacity of Anion Exchange Membranes

Disulfide Dichloride: A High Efficiency Vulcanizing Agent for Sulfurized Polyacrylonitrile

Polymers having stable cationic pendant groups for use as anion exchange membranes and ionomers