Matching Items (3)
Description
Low temperature fuel cells are very attractive energy conversion technology for automotive applications due to their qualities of being clean, quiet, efficient and good peak power densities. However, due to high cost and limited durability and reliability, commercialization of this technology has not been possible as yet. The high fuel cell cost is mostly due to the expensive noble catalyst Pt. Alkaline fuel cell (AFC) systems, have potential to make use of non-noble catalysts and thus, provides with a solution of overall lower cost. Therefore, this issue has been addressed in this thesis work. Hydrogen-oxygen fuel cells using an alkaline anion exchange membrane were prepared and evaluated. Various non-platinum catalyst materials were investigated by fabricating membrane-electrode assemblies (MEAs) using Tokuyama membrane (# A201) and compared with commercial noble metal catalysts. Co and Fe phthalocyanine catalyst materials were synthesized using multi-walled carbon nanotubes (MWCNTs) as support materials. X-ray photoelectron spectroscopic study was conducted in order to examine the surface composition. The electroreduction of oxygen has been investigated on Fe phthalocyanine/MWCNT, Co phthalocyanine/MWCNT and commercial Pt/C catalysts. The oxygen reduction reaction kinetics on these catalyst materials were evaluated using rotating disk electrodes in 0.1 M KOH solution and the current density values were consistently higher for Co phthalocyanine based electrodes compared to Fe phthalocyanine. The fuel cell performance of the MEAs with Co and Fe phthalocyanines and Tanaka Kikinzoku Kogyo Pt/C cathode catalysts were 100, 60 and 120 mW cm-2 using H22 and O2 gases. This thesis also includes work on synthesizing nitrogen doped MWCNTs using post-doping and In-Situ methods. Post-doped N-MWNCTs were prepared through heat treatment with NH4OH as nitrogen source. Characterization was done through fuel cell testing, which gave peak power density ~40mW.cm-2. For In-Situ N-MWCT, pyridine was used as nitrogen source. The sample characterization was done using Raman spectroscopy and RBS, which showed the presence ~3 at.% of nitrogen on the carbon surface.
ContributorsShah, QuratulAin Jawed (Author) / Madakannan, Arunachalanadar (Thesis advisor) / Tamizhmani, Govindasamy (Committee member) / Macia, Narciso (Committee member) / Arizona State University (Publisher)
Created2012
Description
With a recent shift to a more environmentally conscious society, low-carbon and non-carbon producing energy production methods are being investigated and applied all over the world. Of these methods, fuel cells show great potential for clean energy production. A fuel cell is an electrochemical energy conversion device which directly converts chemical energy into electrical energy. Proton exchange membrane fuel cells (PEMFCs) are a highly researched energy source for automotive and stationary power applications. In order to produce the power required to meet Department of Energy requirements, platinum (Pt) must be used as a catalyst material in PEMFCs. Platinum, however, is very expensive and extensive research is being conducted to develop ways to reduce the amount of platinum used in PEMFCs. In the current study, three catalyst synthesis techniques were investigated and evaluated on their effectiveness to produce platinum-on copper (Pt@Cu) core-shell nanocatalyst on multi-walled carbon nanotube (MWCNT) support material. These three methods were direct deposition method, two-phase surfactant method, and single-phase surfactant method, in which direct deposition did not use a surfactant for particle size control and the surfactant methods did. The catalyst materials synthesized were evaluated by visual inspection and fuel cell performance. Samples which produced high fuel cell power output were evaluated using transmission electron microscopy (TEM) imaging. After evaluation, it was concluded that the direct deposition technique was effective in synthesizing Pt@Cu core-shell nanocatalyst on MWCNTs support when a rinsing process was used before adding platinum. The peak power density achieved by the rinsed core-shell catalyst was 618 mW.cm-2 , 13 percent greater than that of commercial platinum-carbon (Pt/C) catalyst. Transmission electron microscopy imaging revealed the core-shell catalyst contained Pt shells and platinum-copper alloy cores. Rinsing with deionized (DI) water was shown to be a crucial step in core-shell catalyst deposition as it reduced the number of platinum colloids on the carbon nanotube surface. After evaluation, it was concluded that the two-phase surfactant and single-phase surfactant synthesis methods were not effective at producing core-shell nanocatalyst with the parameters investigated.
ContributorsAdame, Anthony (Author) / Madakannan, Arunachalanadar (Thesis advisor) / Peng, Xihong (Committee member) / Tamizhmani, Govindasamy (Committee member) / Arizona State University (Publisher)
Created2012
Description
ABSTRACT
Transition metals have been extensively employed to address various challenges
related to catalytic organic transformations, small molecule activation, and energy storage
over the last few decades. Inspired by recent catalytic advances mediated by redox noninnocent
pyridine diimine (PDI) and α-diimine (DI) ligand supported transition metals,
our group has designed new PDI and DI ligands by modifying the imine substituents to
feature donor atoms. My doctoral research is focused on the development of PDI and DI
ligand supported low valent first row metal complexes (Mn, Fe, Co) and their application
in bond activation reactions and the hydrofunctionalization of unsaturated bonds.
First two chapters of this dissertation are centered on the synthesis and
application of redox non-innocent ligand supported low valent iron complexes. Notably,
reduction of a DI-based iron dibromide led to the formation of a low valent iron
dinitrogen compound. This compound was found to undergo a sequential C-H and C-P
bond activation processes upon heating to form a dimeric compound. The plausible
mechanism for dimer formation is also described here.
Inspired by the excellent carbonyl hydrosilylation activity of our previously
reported Mn catalyst, (Ph2PPrPDI)Mn, attempts were made to synthesize second generation
Mn catalyst, which is described in the third chapter. Reduction of (PyEtPDI)MnCl2
furnished a deprotonated backbone methyl group containing Mn compound
[(PyEtPDEA)Mn] whereas reduction of (Ph2PEtPDI)MnCl2 produced a dimeric compound,
[(Ph2PEtPDI)Mn]2. Both compounds were characterized by NMR spectroscopy and XRD
analysis. Hydrosilylation of aldehydes and ketones have been studied using
[(PyEtPDEA)Mn] as a pre-catalyst. Similarly, 14 different aldehydes and 6 different
ii
formates were successfully hydrosilylated using [(Ph2PEtPDI)Mn]2 as a pre-catalyst.
Encouraged by the limited number of cobalt catalysts for nitrile hydroboration, we
sought to develop a cobalt catalyst that is active for hydroboration under mild conditions,
which is discussed in the last chapter. Treatment of (PyEtPDI)CoCl2 with excess NaEt3BH
furnished a diamagnetic Co(I) complex [(PyEtPDIH)Co], which exhibits a reduced imine
functionality. Having this compound characterized, a broad substrate scope for both
nitriles and imines have been investigated. The operative mechanism for nitrile
dihydroboration has been investigated based on the outcomes of a series of stoichiometric
reactions using NMR spectroscopy.
Transition metals have been extensively employed to address various challenges
related to catalytic organic transformations, small molecule activation, and energy storage
over the last few decades. Inspired by recent catalytic advances mediated by redox noninnocent
pyridine diimine (PDI) and α-diimine (DI) ligand supported transition metals,
our group has designed new PDI and DI ligands by modifying the imine substituents to
feature donor atoms. My doctoral research is focused on the development of PDI and DI
ligand supported low valent first row metal complexes (Mn, Fe, Co) and their application
in bond activation reactions and the hydrofunctionalization of unsaturated bonds.
First two chapters of this dissertation are centered on the synthesis and
application of redox non-innocent ligand supported low valent iron complexes. Notably,
reduction of a DI-based iron dibromide led to the formation of a low valent iron
dinitrogen compound. This compound was found to undergo a sequential C-H and C-P
bond activation processes upon heating to form a dimeric compound. The plausible
mechanism for dimer formation is also described here.
Inspired by the excellent carbonyl hydrosilylation activity of our previously
reported Mn catalyst, (Ph2PPrPDI)Mn, attempts were made to synthesize second generation
Mn catalyst, which is described in the third chapter. Reduction of (PyEtPDI)MnCl2
furnished a deprotonated backbone methyl group containing Mn compound
[(PyEtPDEA)Mn] whereas reduction of (Ph2PEtPDI)MnCl2 produced a dimeric compound,
[(Ph2PEtPDI)Mn]2. Both compounds were characterized by NMR spectroscopy and XRD
analysis. Hydrosilylation of aldehydes and ketones have been studied using
[(PyEtPDEA)Mn] as a pre-catalyst. Similarly, 14 different aldehydes and 6 different
ii
formates were successfully hydrosilylated using [(Ph2PEtPDI)Mn]2 as a pre-catalyst.
Encouraged by the limited number of cobalt catalysts for nitrile hydroboration, we
sought to develop a cobalt catalyst that is active for hydroboration under mild conditions,
which is discussed in the last chapter. Treatment of (PyEtPDI)CoCl2 with excess NaEt3BH
furnished a diamagnetic Co(I) complex [(PyEtPDIH)Co], which exhibits a reduced imine
functionality. Having this compound characterized, a broad substrate scope for both
nitriles and imines have been investigated. The operative mechanism for nitrile
dihydroboration has been investigated based on the outcomes of a series of stoichiometric
reactions using NMR spectroscopy.
ContributorsGhosh, Chandrani (Author) / Trovitch, Ryan J. (Thesis advisor) / Seo, Don (Committee member) / Moore, Ana (Committee member) / Arizona State University (Publisher)
Created2018