Thesis
Investigating the origins of interfacial molecular additive improvement of alkaline HER/HOR kinetics on Pt(111)
Master of Science (M.S.), Drexel University
Jun 2022
DOI:
https://doi.org/10.17918/00001074
Abstract
The reversible hydrogen reactions are two of the most fundamental reactions in electrochemistry, but the reasons behind their slowness in alkaline environments is as yet unknown despite many years of research. Understanding the pH dependence of these reactions is important for the commercialization of hydrogen-based electricity generation technologies; acidic fuel cells require expensive Pt-group catalysts that can be surpassed by alkaline counterparts if the rates of these reactions in base are improved. It was recently found that the addition of caffeine to the electrolyte forms a film at the interface that improves both HER and HOR in base and worsens them in acid. This work explores possible sources of this improvement through elucidating the pH dependence of this "caffeine effect" to find the turnover point at which caffeine switches from worsening to improving kinetics. The possibility that caffeine could be buffering the pH at the interface was investigated through the use of buffered electrolytes, but this was thought to be false due to the effect's increase with distance from the pKa. Comparisons with molecules of similar structures were also made in order to identify structural features of this class of "double-layer dopants" that may influence the effect they have at the interface. A set of N-methylimidazoles was selected for these based on previous work identifying the right-side ring of caffeine as the source of the improvement. It was found overall that the pKa of the molecule was influential as the additives typically worsened kinetics in more acidic solutions and improved them in more basic environments; thus, it was thought that the deprotonated molecules influenced HER/HOR in some way, whereas the protonated molecules acted as spectators in acid and blocked active sites. 2-methylimidazole was unearthed as an outlier that also improved the kinetics of HOR in acid. Finally, 1,2,4-triazole helped identify molecule size as an influential parameter as size may affect the orientation of the additives' adsorption onto the Pt surface. Possible theories around the mechanism behind this improvement are proposed based on literature and molecular structure. Future work in the area of probing interfacial water signals and understanding solvent dynamics near the Pt surface is needed to fully understand the reasons behind the slowness of HER/HOR in base as well as the impact of the additives on these reactions.
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Details
- Title
- Investigating the origins of interfacial molecular additive improvement of alkaline HER/HOR kinetics on Pt(111)
- Creators
- Srinidi Badhrinathan
- Contributors
- Joshua Snyder (Advisor)Maureen Han-Mei Tang (Advisor)
- Awarding Institution
- Drexel University
- Degree Awarded
- Master of Science (M.S.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- 50 pages
- Resource Type
- Thesis
- Language
- English
- Academic Unit
- Chemical (and Biological) Engineering (1970-2026); College of Engineering (1970-2026); Drexel University
- Other Identifier
- 991018527910204721