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Carbon-based Materials for Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) in Acidic Media

Mamtani, Kuldeep
http://rave.ohiolink.edu/etdc/view?acc_num=osu149376896628355

Abstract Details

2017, Doctor of Philosophy, Ohio State University, Chemical Engineering.
Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are electrochemical reactions of paramount importance considering the global energy scenario. One of the challenges here is posed by the slow kinetics of these reactions necessitating Pt-based and Ir-based catalysts respectively. The fact that both Pt and Ir are expensive and rare has raised significant interest in the scientific community towards developing low-cost, active and stable ORR and OER catalysts. The present study demonstrates the promise of two carbon-based catalyst materials namely iron-nitrogen-carbon (FeNC) and nitrogen-doped carbon nanostructures (CNx) in this regard. A combination of catalyst synthesis, electrochemical testing and characterization experiments has been used to study ORR and OER on FeNC and CNx catalysts. Valuable insights on the nature of active sites in these catalysts will be instrumental in understanding the detailed ORR mechanisms and designing these catalysts with high active site density. A brief introduction and pertinent literature review on the subject is provided in chapter 1. The principles of electrochemical testing and characterization tools extensively used in this work are discussed in chapter 2. Chapter 3 provides our results on using CO as a probe to investigate the nature of ORR active sites in FeNC catalyst materials. Significant decrease was observed in the ORR activity upon CO exposure demonstrating that Fe is an essential part of ORR active site for FeNC catalyst materials. We attribute this loss in activity to strong binding of CO to FeNC catalyst surface. These results on FeNC catalysts were in sharp contrast to those obtained previously by our group on CNx catalysts where no change in ORR activity was noted after CO exposure. Chapters 4 and 5 present our strategies to identify the actual active sites in FeNC and CNx catalysts. Planar FeN4 (Fe2+, LS) with Fe (II) ion coordinated to four pyrrolic nitrogen atoms and attached to the carbon support was identified as the ORR active site in FeNC catalysts by combining Mossbauer spectroscopy and electrochemical measurements. On the other hand, phosphate ion poisoning was used as a probe for CNx catalysts. Pyridinic-N species on edges of carbon planes were found to be important in imparting ORR activity to CNx. Chapters 6 and 7 demonstrate that FeNC and CNx catalysts are promising bifucntional materials for ORR and OER. They exhibit significantly lower combined overpotential than those by state of the art catalysts namely Pt/C (for ORR) and Ir/C (for OER). The ORR activity, OER activity as well as bifunctionality were found to increase with pyridinic-N content for CNx catalysts. CNx catalysts were resistant to chloride ion poisoning and were extremely stable in HCl electrolyte. This demonstrates their promise as cathode catalysts for oxygen depolarized cathode (ODC)-based HCl electrolysis to manufacture chlorine. Results are described in chapter 8. Chapter 9 points out key conclusions and future research directions.
Umit Ozkan (Advisor)
Anne Co (Committee Member)
Aravind Asthagiri (Committee Member)
Sheryl Szeinbach (Committee Member)
288 p.
Chemical Engineering; Engineering

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Citations

  • Mamtani, K. (2017). Carbon-based Materials for Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) in Acidic Media [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu149376896628355

    APA Style (7th edition)

  • Mamtani, Kuldeep. Carbon-based Materials for Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) in Acidic Media. 2017. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu149376896628355.

    MLA Style (8th edition)

  • Mamtani, Kuldeep. "Carbon-based Materials for Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) in Acidic Media." Doctoral dissertation, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu149376896628355

    Chicago Manual of Style (17th edition)

osu149376896628355
515
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This open access ETD is published by The Ohio State University and OhioLINK.