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Characterization of Electroless Ni-P Coatings and Electrodeposition of Ni Coatings for Electrodes in Zinc-Air Flow Batteries
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- Author / Creator
- Hu, Hang
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Electrochemical energy storage devices such as Li-ion or Zn-air batteries (ZABs) are utilized to store energy generated by renewable sources, since these sources are intermittent. Li-ion batteries uses flammable organic electrolytes (less safe than nonflammable aqueous electrolytes) and have high material costs. ZABs, by comparison, have lower costs, higher safety, lower environmental impact, and higher theoretical energy density than Li-ion batteries. In practice, dendrite formation and passivation on the metallic Zn electrode are major obstacles towards widespread commercialization of ZABs. Circulating the electrolyte has been shown to alleviate these issues; Zn-air flow batteries (ZAFBs), therefore, have better electrochemical performance than ZABs. ZAFBs may be designed to use two sets of electrodes, one set each for the discharge and charge reactions. ZAFBs use “fuel”, a slurry of KOH and Zn particles, that is stored in a “fuel” tank when the battery is not discharging or charging. This design allows energy and power to be decoupled. The ZAFB manufactured by Zinc8 Energy Solutions (shortened to Zinc8) uses a similar design. The regenerator of the ZAFB contains an oxygen evolution electrode for which Ni can be used; electroless Ni-P plating on Mg can be used to fabricate such an electrode.
The first study in this work involved using various materials characterization techniques to identify the composition and microstructure of various Ni-P coatings considered for use by Zinc8. The porosity of these Ni-P coatings was quantified using two methods, a dimple polishing coupled with optical microscopy technique developed in this study and cross sectional observations using scanning electron microscopy (SEM). Porosity quantified from the first technique is referred as macroscopic porosity, while porosity quantified from the second technique is referred as microscopic porosity.
The second study involved electrochemical testing of several coatings. Both immersion testing and cycle testing under OER and hydrogen evolution reaction (HER) conditions. The open circuit voltage (OCV), corrosion potential (Ecorr), and corrosion current density (icorr) were determined. Corrosion rates (CR) were estimated from icorr values. CR values were correlated with microstructural changes (e.g., surface morphology and coating thickness), inherent porosity, and changes in electrolyte composition. High coating porosity generally correlated with high corrosion rates, although with no direct correlation between CR and observed Ni loss for many cases.
The third study focused on developing a low porosity Ni coating from a modified Watts bath. A design of experiments (DoE) approach was taken and Au-coated Si wafers were used as the substrates. Thick (40 μm) coatings were deposited over a fairly short plating time. This process will be adapted for Mg substrates and coating composition will be modified through alloying.
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- Subjects / Keywords
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- Graduation date
- Fall 2023
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.