Poly(norbornene) anion conductive membranes: homopolymer, block copolymer and random copolymer properties and performance

Advanced Energy Materials

Huang

et al. 2020

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218

222

and component manufacturing costs, which are driven by the fact that PEMFCs require specialized component materials due to the highly acidic operating environment. To alleviate these costs, anion exchange membrane fuel cells (AEMFCs) have recently emerged as an alternative to PEMFCs. The higher pH operating environment offers several advantages such as lower material and manufacturing costs. For example, AEMFCs can use platinum group metal (PGM) free cathodes, have more facile oxygen reduction kinetics, [3,4] and may enable a wider range of fuels (e.g., methanol, hydrazine). However, early AEMFC developments suffered from very low overall performance and durability. [5,6] From a durability perspective, cells were mostly believed to be limited by chemical degradation of the anion exchange membrane (AEM) and ionomer at high pH. Because of this, there has been a significant amount of investment targeting the design and manufacturing of stable AEMs and ionomers. As a result, several AEMs have been shown to be stable both at elevated temperature (≥80 °C) and pH for hundreds or even thousands of hours during ex situ testing. [7-11] Another issue that has started to be addressed in the AEMFC literature is water management. Water is formed at the AEMFC hydrogen anode and consumed at the oxygen cathode. As water is produced at the anode, it must be removed to avoid flooding-either through the anode gas stream or, preferably, through the AEM to the cathode (via backdiffusion) where it is needed to react. [12] If too little water is supplied to the cathode by back-diffusion it can dry out; if more water arrives to the cathode than can be reacted, it is also possible for the cathode to flood. Therefore, there is a need for both the anode and cathode catalyst layers to be able to passively transport water. The ability of the ionomer in the catalyst layer to facilitate such ion transport is related to the overall hydrophilicity of the monomers used in the polymer membranes and ionomer. One example where ionomer water uptake has been limiting is the well-known ethylene-tetrafluoroethylene copolymer (ETFE) based powder ionomer. [13] Though the ion exchange capacity (IEC) of that material is modest (only 1.24 meq g −1), The primary function of the ionomers that are incorporated into fuel cell electrode catalyst layers is to provide pathways for ion transport between the catalyst active sites and the electrolyte. This is influenced by many variables, including the ion-exchange capacity, water uptake, and molecular weight. In anion exchange membrane fuel cells (AEMFCs), controlling ionomer water uptake is particularly important and tailoring this property in each electrode is an important consideration when looking to maximize cell performance. In this study, three poly(norbornene) tetrablock copolymer ionomers with a range of physical properties are synthesized and incorporated into AEMFC anode and cathode electrodes. Systematic electrode engineering with these ionomers allows the peak power density to be increased by 100% (1.6 W ...

Section: Resultsmentioning

confidence: 95%

Section: Methodsmentioning

confidence: 99%

Achieving High‐Performance and 2000 h Stability in Anion Exchange Membrane Fuel Cells by Manipulating Ionomer Properties and Electrode Optimization

Hassan

Advanced Energy Materials

Huang

et al. 2020

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218

222

“…The actual anode loading was 0.672 mgPt/Ru cm −2 and for cathode was 0.584 mgPt cm −2 , with no backpressure. Reproduced with permission from Ref [72] ,. Copyright (2020) Royal Society of Chemistry.…”

Section: Anion Exchange Membrane Fuel Cells and Electrolyzersmentioning

confidence: 99%

“…[69][70][71] Very recently, Mandal et al synthesized polynorbornene homopolymer, random copolymer, and block copolymer AEMs and measured their properties and performances. [72] The authors pointed out that the water management to prevent anode flooding and cathode dry out is more critical than the formation of phase segregated morphology in AEMs. To prove this, the authors systematically investigated random copolymer and block copolymer AEMs.…”

Section: Current Status Of Aemfcsmentioning

confidence: 99%

Recent Advancement on Anion Exchange Membranes for Fuel Cell and Water Electrolysis

2020

ChemElectroChem

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Highly conductive anion exchange membranes (AEMs) are one of the few requirements to produce high power during fuel cell operation and for efficient hydrogen production through water electrolysis. The use of chemically stable and cheap AEMs with platinum group metal (PGM)‐free catalysts is suitable for reducing the overall cost of hydrogen production and fuel cell operation. The in situ durability of anion exchange membrane fuel cells (AEMFCs) and anion exchange membrane water electrolyzers (AEMWEs) for several hundred hours is necessary for the widespread application of fuel cell and water electrolysis technologies. This Minireview highlights the best results reported recently in alkaline membrane fuel cells and water electrolysis. The achievable AEMFCs performances are noteworthy using Pt‐free anode and cathode electrocatalysts. Remarkable durability in AEMFCs is witnessed, although the durability is a concern for AEMWEs. Moreover, the current challenges and future directions of AEMFCs and AEMWEs are briefly summarized.

“…[4] Recently, the problems with low ionic conductivity and poor chemical stability of AEMs are systematically addressed. [6][7][8][9][10][11] However, the slow reaction kinetics of oxygen evolution reaction (OER) in AAEMWE reduces the rate and amount of H 2 production. [3,4] A schematic illustration of AAEMWE cell operation is provided below ( Figure 1A).…”

Section: Novel Electrocatalyst For Alkaline Membrane Water Electrolysismentioning

confidence: 99%

Novel Electrocatalyst for Alkaline Membrane Water Electrolysis

2020

ChemElectroChem

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The production of H2 has aroused considerable attention worldwide as a renewable and sustainable energy source for domestic, industrial, and automotive purposes. Currently, about 95 % of H2 is produced from the steam reforming of methane. However, this process leads to the burning of fossil fuels and emits greenhouse gases into the atmosphere. Water electrolysis is an effective strategy to produce H2 in high purity. Alkaline anion exchange membrane water electrolysis (AAEMWE) is preferred to proton exchange membrane water electrolysis (PEMWE) because of the flexibility to be able to use cheaper membranes as separators and non‐noble electrocatalysts. However, the sluggish oxygen evolution reaction (OER) kinetics in AAEMWE is a bottleneck for water splitting efficiency and decreases the overall performances. Now, a novel nickel and iron graphene‐nanoplatelets‐supported metal‐organic framework‐based electrocatalyst has been developed that shows excellent durability and record‐high current density for alkaline electrolysis that outperforms the state‐of‐the‐art OER electrocatalysts.