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Probing the Active Site of CNx Catalysts for the Oxygen Reduction Reaction in Acidic Media: A First-Principles Study

Zhang, Qiang
http://orcid.org/0000-0002-4521-0701
http://rave.ohiolink.edu/etdc/view?acc_num=osu1531312924087566

Abstract Details

2018, Doctor of Philosophy, Ohio State University, Chemical Engineering.
Hydrogen fuel cells, with high energy efficiency and clean emissions, are highly desirable as an alternative to combustion engine using traditional fossil fuels. Proton- exchange membrane fuel cells (PEMFCs) can directly convert hydrogen into electricity and have promising applications in transportation vehicles. However, the commercialization of PEMFCs is hindered by the sluggish oxygen reduction reaction (ORR) at the cathode, which requires expensive platinum (Pt) as catalysts. Low price carbon-based materials, especially nitrogen-doped graphene (CNx) catalysts, are promising candidates to replace Pt, but the lack of knowledge about the active site must be addressed for more optimal catalysts. This study utilized density functional theory (DFT) to investigate the active site(s) of CNx. An extensive set of CNx models, including commonly proposed active sites like pyridinic, quaternary as well as nitrogen-doped carbon vacancies, are examined as possible active sites. Solvation effects are closely investigated by comparing explicit and implicit solvation, as well as a hybrid method. In collaboration with experimentalists, poisoning agents including carbon monoxide and phosphate are investigated to shed light on the nature of the active site. This study demonstrates FeNC and CNx are different materials with distinct active sites. It suggests solvation effects are essential to ORR activity predictions and must be properly included. Different CNx models conform to a volcano activity relationship, where the most active model is associated with an ideal G(OH*). Additionally, ORR activity of individual CNx sites is influenced by several factors including nitrogen doping percentage, graphene layers, and solvation. Carbon vacancies are not ORR active due to unusual strong binding of O*, but some nitrogen-doped carbon vacancies are potential ORR active sites. Phosphate can poison CNx catalysts by adsorbing at the carbon atoms adjacent to nitrogen dopants, blocking ORR intermediates from adsorbing. Our first-principles studies shed light on the active site of CNx as well as important issues with using DFT to study electrochemical reactions on these materials. These results provide insights in the development of high-performance CNx ORR catalysts.
Aravind Asthagiri (Advisor)
Umit Ozkan (Committee Member)
Li-Chiang Lin (Committee Member)
167 p.
Chemical Engineering
ORR; DFT; CNx; Nitrogen-doped graphene; Solvation

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Citations

  • Zhang, Q. (2018). Probing the Active Site of CNx Catalysts for the Oxygen Reduction Reaction in Acidic Media: A First-Principles Study [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1531312924087566

    APA Style (7th edition)

  • Zhang, Qiang. Probing the Active Site of CNx Catalysts for the Oxygen Reduction Reaction in Acidic Media: A First-Principles Study. 2018. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1531312924087566.

    MLA Style (8th edition)

  • Zhang, Qiang. "Probing the Active Site of CNx Catalysts for the Oxygen Reduction Reaction in Acidic Media: A First-Principles Study." Doctoral dissertation, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1531312924087566

    Chicago Manual of Style (17th edition)

osu1531312924087566
190
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This open access ETD is published by The Ohio State University and OhioLINK.