Due to the ability to produce sustainably carbon-based chemicals and fuels, CO2 electrolysis and the closely related CO electrolysis are advancing rapidly from fundamental studies toward industrial applications. Many near...

Anion-exchange membranes (AEM) are being developed for use in electrochemical technologies including fuel cells (AEMFC),water electrolysis (AEMWE for green hydrogen), electrolysers for CO2 reduction (CO2RR), and reverse electrodialysis (RED). Radiation-grafted AEMs (RG-AEM) represent a promising class of AEM that can exhibit high conductivities (OH- conductivities of > 200 mS cm-1 at temperatures above 60 °C) and favourable in situ water transport characteristics). Hence, RG-AEMs have shown significant promise when tested in AEMFCs alongside powdered radiation-grafted anion-exchange ionomers (RG-AEI), producing high performances and promising durabilities [Energy Environ. Sci., 12, 1575 (2019) and Nature Commun., 11, 3561 (2020)], even at temperatures above 100 °C [Dekel et al., J. Power Sources Adv., 5, 100023 (2020)]. An Achilles heel with RG-AEM types is that they can swell excessively in water and have large dimensional changes between the dehydrated and hydrated states. This limits the ion-exchange capacities (IEC) that can be used: excessive IECs in RG-AEM will cause excessive swelling and poorer robustness. This clearly indicates that additional crosslinking is needed. As Kohl et al. have highlighted, optimised crosslinking can lead to production of high-IEC AEMs that are both robust enough to be < 20 µm in thickness and also low swelling [e.g. J. Electrochem. Soc., 166, F637 (2019)], allowing truly world-leading AEMFC performances. RG-AEMs are also being used as a screening platform for down-selecting different (cationic) head-group chemistries for use in RED cells (a salinity gradient power technology), where different head-groups may lead to different AEM characteristics such as: in-cell resistance (when in contact with aqueous electrolytes), permselectivity, and fouling characteristics (when real world waters such as industrial brines, seawater and freshwater are used). It was evident very early on in these studies that RG-AEMs (desirably) exhibit extremely low resistances but also (undesirably) very low permselectivities when un-crosslinked (less than the required 90%+ permselectivity). Our work on RG-type cation-exchange membranes [Sustainable Energy Fuels, 3, 1682 (2019)] clearly shows that introduction of crosslinking can improve permselectivity. Crosslinking always involves a compromise, where its introduction can improve a membrane characteristic (e.g. reduced swelling or improved permselectivity) but also leads to lower conductivities or poorer transport of chemical species through the membranes. Hence, crosslinking types and levels need to be carefully controlled. With RG-AEMs (made by electron-beam activation (peroxidation) of inert polymer films, followed by grafting of monomers and post-graft amination), we have a choice of introducing crosslinking at various stages. The figure below summarises the two different approaches to crosslinking that will be discussed in the presentation: adding a divinyl-type crosslinker into the grafting mixture or adding a diamine-type crosslinker into the amination step. This presentation will present a selection of recent RG-AEM and RG-AEI developments from a number of projects: (1) REDAEM: AEMs for RED cells [EPSRC Grant EP/R044163/1]; (2) CARAEM: Novel RG-AEMs for AEMFCs and AEMWE [EPSRC Grant EP/T009233/1]; (3) SELECTCO2: RG-AEMs being tested in CO2RR cells [EU Horizon 2020 grant agreement 851441]. This presentation will show: (a) RG-AEMs made from thin high density polyethylene (HDPE) precursors appear better for application in AEMFCs, while RG-AEMs from made from thicker ETFE precursors appear to be better for CO2RR cells and RED; (b) RG-AEMs can be made using a variety of crosslinking strategies; (c) RG-AEIs can be made using ETFE powders and give optimal performance after cryogrinding down to micrometer sizes; Figure 1

CO2 electrolysis is a promising technology for a renewable feedstock of carbon-based chemicals. Membrane Electrode Assembly (MEA)-based CO2 electrolysers have been demonstrated to run at commercially relevant current densities. However, the MEA approach can suffer from an unstable production of targeted products, mainly caused by an increase in hydrogen production often within a few hours of operation. We conducted operando measurements in a custom-made electrochemical cell (with an electrode area of 64 mm2) using a high-energy synchrotron X-ray source to study CO2 electrolysis over Cu-based gas diffusion electrodes (GDEs). A series of experiments have been performed between 100 to 250 mA cm−2, showing a change in product distribution as a function of time. Expectedly, this is caused by an increase in water content in the GDE (also called as flooding of GDE) rather than any change of the catalyst itself, e.g. slow depletion of subsurface oxygen. Interestingly, we found that while the increase in water content is causing a gradual degradation of the performance, salt precipitation also had a major influence on water management as well. By having an in-line GC attached to the cell, we could monitor both cathodic and anodic performance as a function of time and relate this to variations in water content throughout the device. Variations in cations played a substantial role in modifying the hydration properties of the device adding an additional effect cations have beyond their role in catalysis. The insights generated from this work will allow future researchers to engineer devices that can maintain proper water management and thus entail long term stability.