Kurapati, Niraja Sona
(2022)
Nanoscale Study of Adsorption-Coupled Electron Transfer Using Scanning Electrochemical Microscopy.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Electron transfer (ET) and specific adsorption of redox-active molecules are coupled in many electrode reactions with practical importance and fundamental interest. For instance, adsorption-coupled electron-transfer (ACET) reactions are involved in many electrode reactions as exemplified by electrocatalysis, electrodeposition, and electro-intercalation.
The ambiguity between concerted and non-concerted mechanisms of ACET reactions limits our current understanding of electrocatalysis. The mechanism of ACET reactions is not well understood and is often represented by the concerted mechanism, e.g., reductive adsorption with O + e ⇌ Rads, where an oxidant, O, is simultaneously reduced and adsorbed as a reductant, Rads, on the electrode surface. Alternatively, the non-concerted mechanism is based on separate outer-sphere ET and adsorption steps, e.g., reduction and adsorption with O + e ⇌ R and R ⇌ Rads, respectively. Both mechanisms are possible when a reductant, R (O₂·⁻, CO₂·⁻, etc.), is reversibly adsorbed on the electrode surface as ubiquitously found in electrocatalysis.
In my PhD work, I demonstrated for the first time that concerted and non-concerted mechanisms of ACET reactions can be discriminated experimentally. We find the non-concerted mechanism for ferrocene derivatives (= R) at highly oriented pyrolytic graphite as simple models. The transient voltammetric mode of nanoscale scanning electrochemical microscopy is enabled by increasing the potential scan rate from 0.1 V/s to 10 V/s to kinetically control the adsorption of ferrocene derivatives, which is required for the discrimination between the two mechanisms. By contrast, CV cannot discriminate the two mechanisms because the adsorption step maintains equilibrium.
The implications of this work are discussed to deepen our mechanistic understanding of electrocatalysis, especially hydrogen electrocatalysis as crucial energy technology. We propose the non-concerted mechanism to provide unprecedented insights as exemplified by resolving current debates on the Tafel analysis and volcano plot based on the controversial concerted model.
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| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
13 August 2022 |
| Date Type: |
Publication |
| Defense Date: |
1 August 2022 |
| Approval Date: |
18 December 2024 |
| Submission Date: |
5 August 2022 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
148 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Dietrich School of Arts and Sciences > Chemistry |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Electrochemistry, Scanning Electrochemical Microscopy |
| Date Deposited: |
18 Dec 2024 19:20 |
| Last Modified: |
19 Dec 2024 13:10 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/43520 |
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