Maier, Maximilian;
(2021)
Towards Improved Understanding of Mass Transport in Polymer Electrolyte Membrane Water Electrolysers.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
The advent of a global societal and governmental movement to curb climate change has put low-carbon technologies at the centre stage of public interest and scientific efforts. In the wake of rising concerns around the carbon footprint of personal mobility and the energy sector, the concept of a ‘Hydrogen Economy’ has experienced yet another rapid spur of popularity. Polymer electrolyte membrane water electrolysers (PEMWEs) are a promising candidate for large-scale hydrogen production, and improvements in the technology have led to increasingly high operational current densities exceeding 2 A cm-2, which requires adequate mass transport strategies to ensure sufficient supply of reactant and removal of products. Optimization and diagnosis of mass transport processes in PEMWEs has long been neglected despite its significance, but the amount of scientific literature has recently increased sharply. This thesis uses existing diagnostic tools to gather new insights into the processes within PEMWE flow channels and liquid-gas diffusion layers, aims at providing new low-cost diagnostic tools to accelerate the investigation of mass transport processes, and consequently deduces novel approaches to the design of PEMWEs components, cells, and stacks. Neutron and X-ray imaging are used to demonstrate the effect of liquid-gas diffusion layer microstructure on the water-gas distribution in a PEMWE, revealing significant inhomogeneity across the active area. Due to cost and accessibility issues around radiation imaging, acoustic methods are explored as alternative diagnostic tools. Acoustic emission is successfully demonstrated as an operando technique to monitor two-phase flow in the flow channels, detecting the transition from bubbly to slug flow. Bubbly flow is observed at the onset of electrochemical activity and low current densities, with a high number of small bubbles, while at higher current densities these small bubbles coalesce and form larger slug bubbles. Lastly, acoustic time-of-flight imaging is used to monitor the water-gas distribution in the liquid-gas diffusion layer and the flow channels, with results being consistent with expectations and previous results obtained via neutron imaging.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Towards Improved Understanding of Mass Transport in Polymer Electrolyte Membrane Water Electrolysers |
| Event: | UCL (University College London) |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2021. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10135728 |
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