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Non-Precious Metal Electrocatalysts for the Oxygen Reduction Reaction in Proton Exchange Membrane (PEM) Fuel Cells

Singh, Deepika
http://rave.ohiolink.edu/etdc/view?acc_num=osu1397727211

Abstract Details

2014, Doctor of Philosophy, Ohio State University, Chemical and Biomolecular Engineering.
Limited availability of fossil fuels have provided a great impetus towards development of efficient energy conversion devices. Proton Exchange Membrane (PEM) fuel cells, that use hydrogen as a fuel and generate energy with water as the only by-product are among such efficient energy conversion devices. Commercial PEM fuel cells use platinum catalyst on the anode and cathode. The Oxygen Reduction Reaction (ORR) on the cathode is a kinetically slow reaction that requires high loadings of platinum on the cathode, thereby significantly increasing the cost of a PEM fuel cell. The associated high cost and limited platinum availability have motivated research towards development of non-precious metal catalysts (NPMCs) for the ORR. NPMCs include transition metal-nitrogen-carbon-coordinated complexes, nitrogen-doped carbon nanostructures (CNx), heat-treated macrocycles, N-graphene, to name a few. A significant challenge has been to develop stable catalysts which can withstand sustained fuel-cell operation. The reason for their degradation is controversial, since there is much debate regarding the active site of these materials. It is unclear if the transition metal, in conjunction with surface nitrogen groups catalyzes the reaction, or merely acts as a catalyst for generation of nitrogen-containing active sites. The studies undertaken in this work are aimed at elucidating the active sites in two specific ORR catalysts, namely, nitrogen-doped carbon nanostructures (CNx) and iron-nitrogen catalysts supported on carbon (Fe-N-C). The growth process of nitrogen-doped carbon nano-structures (CNx) was studied using in-situ and ex-situ characterization techniques. It was found that the Co phase was seen to go through different transformations during the pyrolysis process, depending on the growth substrate used. CNx fibers that formed were acid-washed, and the structure of CNx obtained as well as the nitrogen content was significantly different on the two substrates, which led to activity differences seen in RRDE. CNx and Fe-N-C as two classes of catalysts were studied and compared for activity towards oxygen reduction in acidic medium. While FeNC exhibited a much higher initial activity than CNx, it degraded rapidly in both half-cell and fuel cell, while CNx retained much of its initial activity. The results discussed clarified some of the ambiguity in the role of the transition metal in these two catalysts, and help establish that they are indeed two different materials with different active sites that catalyze ORR. H2S poisoning of Fe-N-C catalysts was undertaken in order to selectively poison specific Fe-sites in these catalysts. It was seen that Fe-N-C-Argon treated only and Fe-N-C-Ar-NH3 treated catalysts exhibited significant differences in behavior after H2S poisoning. Operando X-ray Absorption Spectroscopy (XAS) experiments using electrochemical techniques were also conducted at the Advanced Photon Source of Argonne National Laboratory. XAS, along with other characterization techniques such as X-ray Photoelectron Spectroscopy (XPS), X-ray Difffraction (XRD), Transmission Electron Microscopy (TEM), Temperature Programed Oxidation (TPO), Temperature Programmed Desorption (TPD), etc. have been used to gain insight into the active site of these materials.
Umit Ozkan, Professor (Advisor)
Aravind Asthagiri, Professor (Committee Member)
Jeffrey Chalmers, Professor (Committee Member)
221 p.
Chemical Engineering
Electrochemistry, Catalysis, Proton Exchange Membrane Fuel Cells, Oxygen Reduction Reaction

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Citations

  • Singh, D. (2014). Non-Precious Metal Electrocatalysts for the Oxygen Reduction Reaction in Proton Exchange Membrane (PEM) Fuel Cells [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397727211

    APA Style (7th edition)

  • Singh, Deepika. Non-Precious Metal Electrocatalysts for the Oxygen Reduction Reaction in Proton Exchange Membrane (PEM) Fuel Cells. 2014. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1397727211.

    MLA Style (8th edition)

  • Singh, Deepika. "Non-Precious Metal Electrocatalysts for the Oxygen Reduction Reaction in Proton Exchange Membrane (PEM) Fuel Cells." Doctoral dissertation, Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397727211

    Chicago Manual of Style (17th edition)

osu1397727211
765
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This open access ETD is published by The Ohio State University and OhioLINK.