PhD defence by Na Li
09.07.2021 kl. 13.00 - 16.00
Na Li, Department of Energy Technology, will defend the thesis "A Study on Proton Exchange Membrane Electrolyzer Degradation Test and Mechanism Analysis"
A Study on Proton Exchange Membrane Electrolyzer Degradation Test and Mechanism Analysis
Professor Søren Knudsen Kær
Associate Professor Samuel Simon Araya
Professor Josep M. Guerrero
Professor, Josep M. Guerrero, Aalborg University (Chairman)
Marcelo Carmo, Forschungszentrum Jülich GmbH
Laila Grahl-Madsen, IRD Fuel Cells A/S
Due to the increasingly serious environmental issues and insufficient energy storage, the development of renewable energy and the decarbonization of the economy have been hot research topics as in recent years. Hydrogen is considered by many key in the effort of decarbonizing the economy as it can be used for sector coupling by storing renewable electricity in the form gaseous or liquid fuels via the power to X (PtX) scheme for use in transportation, heating, chemical industry and other industrial sectors. Compared with other electrolyzers, some of the technological advantages such as high H2 purity, high efficiency, high dynamics, quick response, production capacity and more compact design make proton exchange membrane water electrolysis (PEM WE) a promising technology, which can utilize fluctuating renewable energies to produce hydrogen while also providing grid balancing services. However, the capital cost and degradation of components hinder its commercial penetration. Therefore, it’s significantly urgent to analyze the degradation mechanisms and explore corresponding mitigation strategies. The objective of this work is the degradation mechanism analysis of PEM water electrolyzer operated under different conditions.
The effect of ferric ions was firstly investigated by introducing Fe2(SO4)3 solution into DI water to prepare Fe3+ contamination with different concentrations (1, 10, 100 parts per million (ppm, molar ratio)). Results showed that the cell performance reduced obviously with the increase of Fe3+ concentrations, and the concentration of 100 ppm Fe3+ in feed water could lead to sudden cell failure. Besides, the operating parameters of temperature (80 ℃) and current density (2 A cm -2) can make positive contributions to improve cell performance under the condition of contaminated feed water.
In order to fully understand the degradation mechanism of Fe3+ contamination, the long-term test of effect of iron ion contamination on single cell performance was carried out. The test was operated with 1 ppm Fe3+ contamination at the current density of 0.5 A cm -2 and temperature of 60 ℃. The cell performance degrades severely during the contamination test, especially the charge transfer resistances and mass transfer resistances increased significantly with time. The scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDX) tests illustrated the presence of Fe3+ ions on the membrane and catalyst layers on both sides, leading to believe that the Fe3+ transferred from anode through membrane to cathode and accumulated mainly on the cathode, while the presence of fluoride ions on the cathode illustrates that the membrane close to the cathode side is attacked by radicals formed due to Fenton reaction promoted by the presence of Fe3+. Therefore, it is believed that the existence of Fe3+ ions can accelerate the Fenton reaction, resulting in the generation of chemical radicals, which degrade the membrane and anode catalyst layer severely.
Furthermore, the impacts of other cation ions (Fe3+, Cu2+ and Al3+) on the performance of PEM water electrolysis single cells were studied. The prepared 5 ppm contaminated feed solution of each cationic impurity was fed to the PEM water electrolysis system to carry out the tests. Results show that the performance of the single cell decreased initially but then recovered to some degree during the Fe3+ ions contamination. For the case of Cu2+ ions contamination, the ohmic resistance of the cell decreased while the charge transfer resistance showed an increasing trend in the whole test period. The SEM results showed that membrane thinning and catalyst layer degradation happened under both the Fe3+ ions contamination and Cu2+ ions contamination tests. Moreover, the SEM results of the Al3+ contamination test showed a series of cavities on the membrane close to the cathode side, which maybe the reason for the sudden cell failure of this contamination test.
Lastly, to overcome the disadvantages of time-consuming and high costs incurred by the traditional degradation test procedures of PEM water electrolyzer system and its components, novel accelerate stress test (AST) protocols have been proposed in this project. Three different cells were operated at a constant load (1 A cm -2) and two dynamic loads which consist of a low load cycling between 0 A cm -2 (open circuit voltage) and 0.5 A cm -2 and a high load cycling between 1.2 A cm -2 to 2 A cm -2. Polarization and electrochemical impedance spectroscopy (EIS) measurements were carried out to better investigate the performance change of the cells. Results showed that low load cycling test could accelerate the cell performance decay mainly by degrading the cathode catalyst. Even though the high load cycling could lead to increased cell performance due to the reduced ohmic resistance, this dynamic test could accelerate the cell aging by accelerating the membrane thinning.
THE DEFENCE will be IN ENGLISH - all are welcome.
Streaming info - TBD.
Department of Energy Technology