Molecular-Level Insights into Oxygen Reduction Catalysis by Graphite-Conjugated Active Sites
Using a combination of experimental and computational investigations, we assemble a consistent mechanistic model for the oxygen reduction reaction (ORR) at molecularly well-defined graphite-conjugated catalyst (GCC) active sites featuring aryl-pyridinium moieties (N⁺-GCC). ORR catalysis at glassy ca...
| Main Authors: | , , , , , , |
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| Other Authors: | |
| Format: | Article |
| Language: | en_US |
| Published: |
American Chemical Society (ACS)
2018
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| Online Access: | http://hdl.handle.net/1721.1/118382 https://orcid.org/0000-0002-5338-8876 https://orcid.org/0000-0002-6164-485X https://orcid.org/0000-0001-8659-6535 https://orcid.org/0000-0002-6556-3571 https://orcid.org/0000-0001-7111-0176 https://orcid.org/0000-0003-1016-3420 |
| Summary: | Using a combination of experimental and computational investigations, we assemble a consistent mechanistic model for the oxygen reduction reaction (ORR) at molecularly well-defined graphite-conjugated catalyst (GCC) active sites featuring aryl-pyridinium moieties (N⁺-GCC). ORR catalysis at glassy carbon surfaces modified with N⁺-GCC fragments displays near-first-order dependence in O₂ partial pressure and near-zero-order dependence on electrolyte pH. Tafel analysis suggests an equilibrium one-electron transfer process followed by a rate-limiting chemical step at modest overpotentials that transitions to a rate-limiting electron transfer sequence at higher overpotentials. Finite-cluster computational modeling of the N⁺-GCC active site reveals preferential O₂ adsorption at electrophilic carbons alpha to the pyridinium moiety. Together, the experimental and computational data indicate that ORR proceeds via a proton-decoupled O₂ activation sequence involving either concerted or stepwise electron transfer and adsorption of O₂, which is then followed by a series of electron/proton transfer steps to generate water and turn over the catalytic cycle. The proposed mechanistic model serves as a roadmap for the bottom-up synthesis of highly active N-doped carbon ORR catalysts. Keywords: density functional theory; electrocatalysis; mechanistic studies; N-doped carbon; oxygen reduction |
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