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Structural and Photo-Electrochemical Properties of Molybdenum Disulfide and Carbon Foam Composites /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Structural and Photo-Electrochemical Properties of Molybdenum Disulfide and Carbon Foam Composites // Gregory M Jensen.
Author:	Jensen, Gregory M.,
Description:	1 electronic resource (187 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 87-01, Section: B.
Contained By:	Dissertations Abstracts International87-01B.
Subject:	Chemistry. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=32184393
ISBN:	9798286450763

Structural and Photo-Electrochemical Properties of Molybdenum Disulfide and Carbon Foam Composites /
Jensen, Gregory M.,

Structural and Photo-Electrochemical Properties of Molybdenum Disulfide and Carbon Foam Composites /Gregory M Jensen. - 1 electronic resource (187 pages)

Source: Dissertations Abstracts International, Volume: 87-01, Section: B.

This dissertation highlights scalable production techniques and characterization of a two-dimensional (2D) transition metal dichalcogenide (TMD) material, molybdenum disulfide (MoS2), and its application in a foamed carbon composite for electrocatalysis. The first project of this dissertation discusses the investigation of an anomalous MoS2 growth pattern displaying venation-like patterns of raised material observed from the ?precursor free? chemical vapor deposition (CVD) technique implemented by our group. Reproducible growth of this anomalous growth with enhanced coverage of the substrate was achieved by isolating the required growth parameters. To create this material at least 10 mg of sulfur powder is necessary, as well as a seasoned (well used) graphite boat to hold the substrate and a growth step at temperatures at least 50 ?C above the standard growth temperature for MoS2, which means temperatures above 800 ?C. Optical microscope imaging confirmed the structure of the growth, which had two trends: a primary growth pattern perpendicular to the seeding point, and a secondary parallel to the seeding point. Atomic force microscopy (AFM) was measured on the patterns to determine their average height, 50.40 nm for the primary pattern and 54.84 nm for the secondary, and periodicity, ~3.5 ?m for the primary pattern and ~1.16 ?m for the secondary. Both photoluminescence (PL) and Raman spectroscopy were used to optically characterize the material on a flat and raised region. The PL showed a comparative red-shifting of the A exciton peak while both the Raman E12g and A1g peaks decreased in Raman shift. These results indicate the presence of strain in the material, specifically in the flat regions between the raised MoS2 patterns.The second project of this dissertation covered the fabrication of carbon foam (CF) substrates using the batch-process method, which were used to create an MoS2-CF composite material by sulfurizing various Mo sources as comparisons to determine the most efficient technique. The Mo sources and techniques used were MoO3 powder directly applied to the CF substrate surface, RF sputtering 360 nm of Mo which was oxidized and sulfurized, and MoO3 powder mixed with coal precursor powder then foaming using the standard process. Each Mo source produced MoS2 on the surface of the CF substrate, with sputtered Mo and the MoO3 powder mixture producing composites with similar surface structures to the CF substrate, seen using scanning electron microscope (SEM) imaging. Raman spectroscopy of all MoS2-CF composites indicate bulk crystal growth with all E12g and A1g peak separations above 26 cm-1. Additionally, energy dispersive x-ray spectroscopy (EDS) and x-ray photoelectron spectroscopy (XPS) measurements confirmed similar elemental compositions and chemical state information about the CF substrate and the MoS2-CF composites.The final project of this dissertation implements the results of the previous project to create MoS2-CF composites used for electrocatalysis. The batch-process method was used to integrate seeding points for MoS2 on the surface of CF substrates by fabricating CF composites with MoO3 and MoS2 powders mixed separately with the coal precursor powder and at concentrations of 1, 2.5, and 5 wt.%. After sulfurizing the green CF composites, the MoS2-CF materials were characterized via SEM imaging, Raman spectroscopy, and EDS. The MoS2-CF composites were then used to make working electrodes for use in a 3-electrode cell for photo-chemical and electrochemical measurements, which showed the composites were stable in 0.5 M H2SO4, and most electrodes reached a current density of -10 mA cm-2 between 200-500 mV. Differences between the MoO3 and MoS2 precursor sources resulted in a 40% smaller magnitude overpotential, and a 75% larger concentration averaged photo-response, for MoO3 precursor-based composites compared with MoS2 precursor-based composites. Overall, the batch-process method provided a simple and scalable method to fabricate well performing MoS2-CF composite electrocatalysts.

English

ISBN: 9798286450763Subjects--Topical Terms:

516420
Chemistry.
Subjects--Index Terms:

Molybdenum disulfide

Structural and Photo-Electrochemical Properties of Molybdenum Disulfide and Carbon Foam Composites /
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520 $a This dissertation highlights scalable production techniques and characterization of a two-dimensional (2D) transition metal dichalcogenide (TMD) material, molybdenum disulfide (MoS2), and its application in a foamed carbon composite for electrocatalysis. The first project of this dissertation discusses the investigation of an anomalous MoS2 growth pattern displaying venation-like patterns of raised material observed from the ?precursor free? chemical vapor deposition (CVD) technique implemented by our group. Reproducible growth of this anomalous growth with enhanced coverage of the substrate was achieved by isolating the required growth parameters. To create this material at least 10 mg of sulfur powder is necessary, as well as a seasoned (well used) graphite boat to hold the substrate and a growth step at temperatures at least 50 ?C above the standard growth temperature for MoS2, which means temperatures above 800 ?C. Optical microscope imaging confirmed the structure of the growth, which had two trends: a primary growth pattern perpendicular to the seeding point, and a secondary parallel to the seeding point. Atomic force microscopy (AFM) was measured on the patterns to determine their average height, 50.40 nm for the primary pattern and 54.84 nm for the secondary, and periodicity, ~3.5 ?m for the primary pattern and ~1.16 ?m for the secondary. Both photoluminescence (PL) and Raman spectroscopy were used to optically characterize the material on a flat and raised region. The PL showed a comparative red-shifting of the A exciton peak while both the Raman E12g and A1g peaks decreased in Raman shift. These results indicate the presence of strain in the material, specifically in the flat regions between the raised MoS2 patterns.The second project of this dissertation covered the fabrication of carbon foam (CF) substrates using the batch-process method, which were used to create an MoS2-CF composite material by sulfurizing various Mo sources as comparisons to determine the most efficient technique. The Mo sources and techniques used were MoO3 powder directly applied to the CF substrate surface, RF sputtering 360 nm of Mo which was oxidized and sulfurized, and MoO3 powder mixed with coal precursor powder then foaming using the standard process. Each Mo source produced MoS2 on the surface of the CF substrate, with sputtered Mo and the MoO3 powder mixture producing composites with similar surface structures to the CF substrate, seen using scanning electron microscope (SEM) imaging. Raman spectroscopy of all MoS2-CF composites indicate bulk crystal growth with all E12g and A1g peak separations above 26 cm-1. Additionally, energy dispersive x-ray spectroscopy (EDS) and x-ray photoelectron spectroscopy (XPS) measurements confirmed similar elemental compositions and chemical state information about the CF substrate and the MoS2-CF composites.The final project of this dissertation implements the results of the previous project to create MoS2-CF composites used for electrocatalysis. The batch-process method was used to integrate seeding points for MoS2 on the surface of CF substrates by fabricating CF composites with MoO3 and MoS2 powders mixed separately with the coal precursor powder and at concentrations of 1, 2.5, and 5 wt.%. After sulfurizing the green CF composites, the MoS2-CF materials were characterized via SEM imaging, Raman spectroscopy, and EDS. The MoS2-CF composites were then used to make working electrodes for use in a 3-electrode cell for photo-chemical and electrochemical measurements, which showed the composites were stable in 0.5 M H2SO4, and most electrodes reached a current density of -10 mA cm-2 between 200-500 mV. Differences between the MoO3 and MoS2 precursor sources resulted in a 40% smaller magnitude overpotential, and a 75% larger concentration averaged photo-response, for MoO3 precursor-based composites compared with MoS2 precursor-based composites. Overall, the batch-process method provided a simple and scalable method to fabricate well performing MoS2-CF composite electrocatalysts.
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