Li, Boyang
(2024)
Computational Study of Manganese, Nitrogen Co-doped Carbon as Electrocatalysts in Proton Exchange Membrane Fuel Cell.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Renewable energy technologies have been actively pursued in order to meet increasing energy demand and mitigating environmental pollution. Proton exchange membrane fuel cell (PEMFC) is a promising technology with a high energy conversion efficiency to replace the traditional internal combustion engine in automobiles while producing no greenhouse emission. However, the high cost of Pt based electrocatalysts for promoting oxygen reduction reaction (ORR) at the cathode hampers the widespread application of PEMFCs. Showing encouraging performance, non-precious transition metal and nitrogen co-doped carbon electrocatalysts have been extensively developed as cost-effective ORR catalysts in PEMFCs.
This research aims to predict the chemical nature of active sites, kinetic activity for ORR, and structural stability in electrochemical conditions of Mn and N co-doped carbon (denoted as Mn-N-C) catalyst using the first principles density functional theory (DFT) methods. Both D1 type MnN4 (i.e., a Mn atom coordinated with four pyrrolic N) and D2 type MnN4 (i.e., a Mn atom coordinated with four pyridinic N) moieties embedded in a carbon graphene layer have been predicted to be active for four-electron ORR in acid media, explaining well available experimental measurement results. Notably, the D1 site was predicted to have a superior limiting potential of 0.80 V for ORR, as compared to the value of 0.54 V on the D2 site, indicating a higher intrinsic ORR activity on the D1 sites. By contrast, the D2 site has been predicted to exhibit enhanced electrochemical stability over the D1 site, as evidenced by the predictions that the free energy change for demetallation process is 0.36 eV higher for the D2 site than the D1 site. Moreover, a constant potential computational method combined with a microkinetic model for ORR has been developed and applied to predict the half-wave potential of ORR to be 0.73 V on D2 site, agreeing well with experimental values to validate the developed computational approach. Motivated by the predicted stability of two types of MnN4 sites, the free energy evolution along a transformation pathway from D1 to D2 site has been computed to examine novel synthesis concept for enhancing the electrochemical stability of Mn-N-C catalysts.
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Details
| Item Type: |
University of Pittsburgh ETD
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| Status: |
Unpublished |
| Creators/Authors: |
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| ETD Committee: |
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| Date: |
16 February 2024 |
| Defense Date: |
27 February 2024 |
| Approval Date: |
3 June 2024 |
| Submission Date: |
20 February 2024 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
110 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Mechanical Engineering and Materials Science |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
proton exchange membrane fuel cell, oxygen reduction reaction, non-precious metal catalyst, density functional theory, adsorption energy, activation energy, nudged elastic band, microkinetic model, solvation model |
| Related URLs: |
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| Date Deposited: |
03 Jun 2024 14:37 |
| Last Modified: |
03 Jun 2024 14:37 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/45811 |
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