The optimisation of alkaline membrane fuel cell electrodes containing anion-exchange powder ionomers
Creators: name: Salam, Ihtasham
Publisher: name: University of Surrey
Year: 2023

description: Energy security is turning into a widely discussed topic in the current climate around the world. Global warming, finite fossil fuel deposits, environmental pollution, and the ever-increasing atmospheric CO2 levels are all intertwined issues which are evoking responses across a wide array of different sectors which includes the scientific industry for novel technological developments in which fuel cells can play an important role.<br>
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description: There are a variety of fuel cells for different operational requirements, and in this project the focus is on anion-exchange membrane fuel cells (AEMFCs). Previously, a lot of research and development has gone into the anion-exchange membrane (AEM) and catalysts, and these are still the key items of focus in literature. However, the anion-exchange ionomer (AEI) is also an important component within AEMFCs where it is embedded in the catalyst layer (CL) functioning as an anion conduction agent across the CL in addition to improving CL adhesion.<br>
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description: This research project is aimed at studying different milling treatments including ball milling and cryomilling of the AEI at three distinct stages of AEI synthesis. Use of spectroscopic analytical tools, such as Raman, FT-IR, and SS NMR, showed no absence of any particular peak post-milling, signifying no degradation. Raman spectroscopy was used in more detail to assess quantitative changes to peak intensity where it highlighted decreases or lowest increases for certain peaks associated with the ETFE polymer backbone constituent (521 cm-1, 945 cm-1, and 1042 cm-1) across all three synthetic stages. While other peak intensity variations were associated with changes to the crystallinity character. These aforementioned techniques were also used to confirm chemical transformations at each synthetic stage.<br>
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description: Milling at the third, final synthetic stage of the AEI was deemed most suitable as particles showed a tendency to re-agglomerate heavily after final synthetic procedure (amination of ETFE-g-poly(VBC)). Morphological assessment highlighted cryomilling to be the most effective method for reducing particle size (11 ± 11 μm) in comparison to ball milling (101 ± 61 μm) vs. the non-milled AEI (160 ± 210 μm) at the final synthetic stage. Ball milling also showed a tendency to fuse particle together instead of breaking them apart at the initial two synthetic stages (e.g. 20 μm  310 μm at pristine ETFE stage). Meanwhile thermal assessment such as TGA showed negligible thermal profiles alterations while DSC showed subtle Tg shifts indicating crystallinity changes of milled samples, especially ball milled samples.<br>
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description: Finally, electrode CLs composed of cryomilled and non-cryomilled AEI were analysed using EDX and showed more homogenous distribution across the CL for the cryomilled AEI whilst SEM data showed higher porosity at the anode and lower porosity at the cathode CL compared with the non-cryomilled sample. Subsequent fuel cell testing showed the cryomilled AEI produced on average peak power density (PPD) improvement of 0.11 ± 0.00 W cm-2 under CO2-free air and 0.16 ± 0.01 W cm-2 under O2 cathode fuels. These findings highlight the importance of different milling methods of AEIs and how it can influence CL morphology and the associated fuel cell performances.<br>