Structurally Enhanced Electrodes for Redox Flow Batteries Produced via Electrospinning
Bibliographic record
Abstract
The vanadium redox flow battery is one of the most promising secondary batteries for energy storage system due to its design flexibility attributed to the large adjustable capacity of the storage tanks filled with electrolyte solution. However, the vanadium redox flow battery is not yet widely deployed owing to its low power density. This thesis describes the way of constructing the fibrous electrode with novel structure to overcome the flaw. The general electrospun materials of polyacrylonitrile were synthesized with substantially lower porosity than standard materials by applying compression during the stabilization stage. This objective was to create flow battery electrodes with higher volumetric surface area. The flexibility of the electrospinning technique combined with adjustable post-processing steps such as stabilization and carbonization allowed for the creation of layers with very specific structural and transport properties. In-plane permeability was found to remain relatively constant compared to the original uncompressed fibrous structure. On the other hand, the fibers compacted and compressed down to the flat ribbon shape hurt the through-plane permeability, so artificial holes were created using a CO_2 laser to perforate the structure. The loss of specific surface area caused by laser perforation was quite negligible and still showed improvement. Overall, the novel flow-through electrode provided from this study successfully contributed to improving the transport properties as well as the electrochemical reaction rate, leading to the optimal power density of a vanadium redox flow battery. In addition to that, 2-dimensional half-cell model was created with multi-physics simulation to predict the change in performance with respect to the structural properties of fibrous electrode. The performance was evaluated based on polarization behavior, required pumping power to operate the cell, and operating efficiency. Moreover, electrode was constructed to multi-layered structure in profiles of permeability, fiber size, and porosity. The vanadium ion could be distributed uniformly over the entire region of electrode, which enabled more portion of fiber surface to be utilized for reaction to improve power density while maintaining low pumping power for operation. Based on the prediction from the model, the actual experimental work was invested for multi-layered structure built with novel electrospun fibrous layers. Two different flow channel designs were considered: interdigitated and parallel. The convective flow was induced with the interdigitated flow channel design. Thus, the vanadium ions could be distributed effectively to the region of electrode, resulting in the higher power density. The electrode created in multi-layer provided higher net power density even though the increased pumping power requirement compared to the case of single layer. The body of work presented in this thesis has contributed significantly to understanding the mass transport phenomena taking place in electrodes built in novel fibrous structures. It highlights the preparation of this media through electrospinning as well as numerical and experimental methods for characterizing and understanding these processes. All the work presented here promoted the development of flow batteries through better understanding of the flow battery electrode.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".