- Title
- Gradient morphologies for electrodeposited manganese dioxide to enhance energy storage
- Creator
- Mujammami, Fahad Jubran
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2021
- Description
- Masters Research - Master of Philosophy (MPhil)
- Description
- In the previous studies, thin films MnO2 was synthesised by using direct potential at different total time deposition, and the synthesised material observed dense and crack materials as well as the limitation of ion diffusion into the electrode surface. In this thesis, the change of morphology of synthesis thin films MnO2 due to the mass transfer and performance change of the electrode surface during the electrodeposition process as well as change of synthesised material electrodeposition by applying pulsed potential has been illustrated. The reason of using this method is to enhance ion diffusion and improve synthesised porous materials. The stability of different materials has also been studied. The initial investigation of thin films MnO2 deposition has focused on the different parameters, including duty cycle, number of electrodeposition step, step time, rest time, different pulse potential, and electrolyte composition. From this experiment, the results of capacitive behaviour showed a high performance and the improvement of material structure. In addition, the main important focusing in this study is to optimise the morphology of MnO2 to use in different conversion application and electrochemical energy storage as well as the considering of thickness deposition MnO2 is to apply in batteries system. This studied showed the specific capacitance has reportedly increased at least 20% more than the material mentioned in the previous studies that used constant potential electrodeposition. The high performance and stability of synthesised material has been observed at short duty cycle due to less thickness of material, however, the capacitance and stability has decreased at long duty cycle due to high-deposited mass. The enhancement of specific capacitance is found to be related to the structural improvement, which allowed the electrolyte to access the synthesised material. At long duty cycle, it is found that the deposited mass of MnO2 is increased due to the increase of double layer capacitance where the ion diffusion is increased from the bulk solution with long rest time. However, at short duty cycle, the deposited mass is decreased resulting from the double layer capacitance, which is decreased as well as the ion diffusion is decreased from the bulk of electrolyte solution into the electrode surface. Furthermore, it has been observed that the diffusion of materials has increased with the increase of number of steps deposition since the calculated mass of deposited material has increased. The deposited mass is found to be decreased while long steps deposition has been applied and vice versus. When considering the electrolyte concentration, the high performance of the synthesised material has been noticed with 0.01 M of Mn2+ and 0.1 M H2SO4. The mass deposition is found to be increased with the increase of Mn2+ concentration; however, it has caused a low performance of the synthesised material due to the increase of thickness deposition. At considering different applied potentials, the deposited mass of synthesised material increased with the increase of applied potential. However, while the applied potential has been increased over 1.5 V, the oxygen evolution increases dramatically, which has affected the synthesised material structure and has resulted an exponential increase of the deposited mass. In addition, a step potential electrochemical spectroscopy has been utilised in order to provide more information about the mechanism of synthesised material. It provides a better insight of the change capacitance during both electric double layer capacitance and pseudeocapacitance as a function of deposited material fraction as well as film thickness. The change of capacitance has been investigated at different duty cycles. At short duty cycle, the total capacitance of synthesised material is found to depend on the response of both double layer capacitance and pseudeocapacitance. On the other hand, with long duty cycle, the increase of electric double layer is blocked the pores of synthesised material as the thickness of synthesised material is increased on the electrode surface. This increase of deposited material film thickness leads to decrease pseudeocapacitance behaviour. The synthesis material of MnO2 is contributed from the transition of Mn(III) to Mn(IV) states as a change of ion diffusion of synthesised material. Further, the synthesised thin films MnO2 has been observed from various thin film MnOOH deposited on the surface of electrodes, which explains the behaviour of pseudeocapacitance.
- Subject
- gradient morphologies; electrodeposited; manganese; dioxide
- Identifier
- http://hdl.handle.net/1959.13/1509866
- Identifier
- uon:56321
- Rights
- Copyright 2021 Fahad Jubran Mujammami
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 10 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 235 KB | Adobe Acrobat PDF | View Details Download |