Abstract
Abstract One promising way to store and distribute large amounts of renewable energy is water electrolysis, coupled with transport of hydrogen in the gas grid and storage in tanks and caverns. The intermittent availability of renewal energy makes it difficult to integrate it with established alkaline water electrolysis technology. Proton exchange membrane (PEM) water electrolysis (PEMEC) is promising, but limited by the necessity to use expensive platinum and iridium catalysts. The expected solution is anion exchange membrane (AEM) water electrolysis, which combines the use of cheap and abundant catalyst materials with the advantages of PEM water electrolysis, namely, a low foot print, large operational capacity, and fast response to changing operating conditions. The key component for AEM water electrolysis is a cheap, stable, gas tight and highly hydroxide conductive polymeric AEM. Here, we present target values and technical requirements for AEMs, discuss the chemical structures involved and the related degradation pathways, give an overview over the most prominent and promising commercial AEMs (Fumatech Fumasep® FAA3, Tokuyama A201, Ionomr Aemion™, Dioxide materials Sustainion®, and membranes commercialized by Orion Polymer), and review their properties and performances of water electrolyzers using these membranes.
Highlights
This overview focuses on a selected range of membranes, which have been tested for their use in anion exchange membrane (AEM) water electrolysis, and have been or are available to researchers through companies
One answer to this problem is the use of hydrogen-based energy storage systems (ESS): Excess electric energy can be transformed into hydrogen by water electrolysis, the produced hydrogen can be stored in large tanks, underground caverns [1] or fed into the existing natural gas grid, allowing efficient transport of energy to the demand sites, where hydrogen again can be used to produce electric energy either in fuel cells or by powering gas turbines
Cell performance is comparable to that with carbonatebased circulating medium. This indicates that a comparable ionic contact between the catalyst and AEM is obtained for cells with ionomer binder and cells with inert binder/1 wt% carbonate solution
Summary
This overview focuses on a selected range of membranes, which have been tested for their use in anion exchange membrane (AEM) water electrolysis, and have been or are available to researchers through companies (we refer to this as commercial membranes). Charges are transferred over the membrane by hydroxide ions, as in alkaline water electrolysis, and the resulting high pH of the system reduces corrosion issues of the components: titanium in the porous transport layers (PTL) and bipolar plates (BPP) can be substituted by steel, and the scarce platinum group metals (PGM) in the electrodes can be substituted by cheap and abundant materials like nickel. The degradation of polymer backbones, leading to chain scission, decreases the molecular weight This results in increased brittleness of the membrane and is especially pronounced in the presence of aromatic ether groups [24,25,26]. The latter has the potential advantage that gases need to diffuse around the added nanoparticles, and the increased tortuosity reduces the permeability for gases [57]
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