Faculty Mentor Information
Dr. Claire (Hui) Xiong, Boise State University
Presentation Date
7-2025
Abstract
Lithium-ion batteries have been frequently utilized for storing energy due to their high energy density. Nanoporous metal oxides, including tantalum oxide (Ta₂O₅) have many uses in the field ranging from electrodes for the purposes of energy storage to biomaterials. Anodization, the process of using an electric current to cover a metal with an oxide layer, is one method for oxide layer growth because it is cost-effective and can be easily fine tuned. Ta₂O₅ is chemically inert and has electrochemical properties, however, current anodization methods generally use dangerous and corrosive anodization conditions. This project studies the effect of electropolishing, a process that polishes a metal surface by removing material from the bumps on the surface using electricity, on the surface roughness of tantalum metal, as well as the effect of surface roughness on the structure of Ta₂O₅ nanopores. The sample included pieces of tantalum foil, which were electropolished and anodized. Electropolishing works on a similar principle to reverse electroplating. In this study, two pieces of tantalum foil were suspended in a dilute sulfuric acid/methanol solution. An electric current was run through this solution. This etched material away from the piece of foil, ideally rendering it perfectly flat. Current and power were set to a different value each time until the optimal combination was found. After the Electropolishing was finished, the foil was then anodized. The foil was suspended in a potassium phosphate/glycerol solution. The non-electropolished piece of tantalum was replaced with a piece of platinum mesh. As current ran through these electrodes, an oxide layer formed on the surface of the tantalum. This layer was simultaneously grown and etched away, forming pores on the surface. The anodization process was also done on an as-received piece of tantalum. At the conclusion of electropolishing and anodization of the tantalum samples in this study, it was observed through use of a scanning electron microscope (SEM) imaging that the flat electropolished sample had larger, more ordered pores than the as-received sample, which had a rougher surface to begin with. It was observed that the surface roughness on Ta₂O₅ nanopores made the oxide layer more irregular and the pores smaller. This study shows that decreased surface roughness improves the structure of the oxide layer, which can improve electrochemical performance. Recommendations for future research include altering anodization conditions instead of electropolishing conditions, in order to observe the effects on the oxide layer. Other future research could examine whether other metal oxides respond the same as Ta₂O₅ to surface roughness.
The Effect of Surface Roughness on the Nanopore Structure of Tantalum Pentoxide
Lithium-ion batteries have been frequently utilized for storing energy due to their high energy density. Nanoporous metal oxides, including tantalum oxide (Ta₂O₅) have many uses in the field ranging from electrodes for the purposes of energy storage to biomaterials. Anodization, the process of using an electric current to cover a metal with an oxide layer, is one method for oxide layer growth because it is cost-effective and can be easily fine tuned. Ta₂O₅ is chemically inert and has electrochemical properties, however, current anodization methods generally use dangerous and corrosive anodization conditions. This project studies the effect of electropolishing, a process that polishes a metal surface by removing material from the bumps on the surface using electricity, on the surface roughness of tantalum metal, as well as the effect of surface roughness on the structure of Ta₂O₅ nanopores. The sample included pieces of tantalum foil, which were electropolished and anodized. Electropolishing works on a similar principle to reverse electroplating. In this study, two pieces of tantalum foil were suspended in a dilute sulfuric acid/methanol solution. An electric current was run through this solution. This etched material away from the piece of foil, ideally rendering it perfectly flat. Current and power were set to a different value each time until the optimal combination was found. After the Electropolishing was finished, the foil was then anodized. The foil was suspended in a potassium phosphate/glycerol solution. The non-electropolished piece of tantalum was replaced with a piece of platinum mesh. As current ran through these electrodes, an oxide layer formed on the surface of the tantalum. This layer was simultaneously grown and etched away, forming pores on the surface. The anodization process was also done on an as-received piece of tantalum. At the conclusion of electropolishing and anodization of the tantalum samples in this study, it was observed through use of a scanning electron microscope (SEM) imaging that the flat electropolished sample had larger, more ordered pores than the as-received sample, which had a rougher surface to begin with. It was observed that the surface roughness on Ta₂O₅ nanopores made the oxide layer more irregular and the pores smaller. This study shows that decreased surface roughness improves the structure of the oxide layer, which can improve electrochemical performance. Recommendations for future research include altering anodization conditions instead of electropolishing conditions, in order to observe the effects on the oxide layer. Other future research could examine whether other metal oxides respond the same as Ta₂O₅ to surface roughness.
Comments
Financial support was provided by ACS Project SEED and DoD award FA9550 23 1 0507. S. Pooley gratefully acknowledges support from the National Science Foundation Graduate Research Fellowship Program under Grant No. 1946726.