Type
Text
Type
Dissertation
Advisor
Wong, Stanislaus | Khalifah, Peter G | Parise, John | Stacchiola, Dario.
Date
2015-08-01
Keywords
Chemistry
Department
Department of Chemistry.
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/77094
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
Hydrogen fuel cells are expected to be a key energy conversion technology in the future due to their high efficiency. However, traditional Pt electrocatalysts used in fuel cells are limited in both their cost and availability. It is therefore desirable to develop non-noble metal cathode catalysts as alternatives for the oxygen reduction reaction (ORR) of fuel cells. In this study, binary and ternary molybdenum oxynitrides and nitrides have been designed as electrocatalysts for ORR in fuel cells. Ammonia-treated carbon-supported cobalt molybdenum oxynitrides (CoxMo1-xOyNz/C) with rock salt structure have been investigated. These oxynitrides show moderate activity in acidic electrolyte and excellent activity in alkaline electrolyte. It is found that synthesis temperature and composition impact the catalytic activity. Co0.50Mo0.50OyNz/C treated at 823 K exhibits the highest ORR activity in both electrolytes. This oxynitride demonstrates reasonable stability during long-term operation in either medium. X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM) studies indicate that ionic cobalt is doped into the rock salt structure, though some metallic cobalt is also produced as a byproduct during the ammonolysis. The formation of bimetallic cobalt molybdenum oxynitride is responsible for the ORR activity. The ORR activities of binary molybdenum nitrides with two different crystal structures illustrate that hexagonal molybdenum nitrides (delta-MoN and Mo5N6) exhibit enhanced activity over Mo2N with the rock salt type cubic structure. In order to further enhance the activity, bimetallic Co0.6Mo1.4N2 was synthesized via a two-step solid state reaction. This hexagonal ternary nitride contains four-layered stacking sequence with alternating layers of transition metals in octahedral and trigonal prismatic coordination. The octahedral sites contain a mixture of divalent Co and trivalent Mo, while the trigonal prismatic sites contain Mo with a higher oxidation state. Co0.6Mo1.4N2 shows a better ORR activity than delta-MoN. In addition, Co0.6Mo1.4N2 is demonstrated to be a highly active and stable electrocatalyst for hydrogen evolution reaction (HER) in acid solution. | 186 pages
Recommended Citation
Cao, Bingfei, "Investigations of Non-noble Metal Based Oxynitrides and Nitrides as Electrocatalysts for Oxygen Reduction Reaction and Hydrogen Evolution Reaction" (2015). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 2931.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/2931