Browsing by Author "Gokagac, Gulsun"

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Activity of Carbon-Supported Platinum Nanoparticles Toward Methanol Oxidation Reaction
(Amer Chemical Soc, 2007) Sen, Fatih; Gokagac, Gulsun
Two groups of carbon-supported platinum nanoparticle catalysts have been prepared. In group 1, catalysts I and 11 were prepared using PtCl4 and H2PtCI6 as starting materials and 1-hexanethiol, HSCH2CH2CH2CH2CH2CH3, as a surfactant. For group 11, the same platinum complexes were used as starting materials (catalyst III from PtCl4, catalyst IV from H2PtCl6) and tert-octanethiol, HSC(CH3)(2)CH2CH2CH2CH2CH3, was used as a surfactant for the first time. It has been found that the group II catalysts are between similar to 2 and similar to 3.3 times more active toward methanol oxidation reaction compared to other prepared and commercial catalysts. Transmission electron microscopy shows that the platinum nanoparticles are homogeneously dispersed on the carbon support and exhibit a narrow size distribution; the average particle size was found to be 2 +/- 0.4 and 3 +/- 0.4 nm in diameter for group I and group II catalysts, respectively. X-ray diffractogram analysis indicates that the platinum nanoparticles have a face centered cubic structure consistent with that of platinum metal itself., X-ray photoelectron spectra of the catalysts indicate two different types of platinum with the Pt 4f(7/2) binding energies of 71.1, 74.4 eV; 71.3, 74.3 eV; 71.0, 74.4 eV; and 71.5, 74.5 eV for catalysts I-IV, respectively. These have been identified as Pt(0O) and Pt(IV), which could be platinum oxide or hydroxide. By looking at the oxidation state data, we found that catalysts I-IV consist of 71% Pt(0) and 29% Pt(IV); 83% Pt(0) and 17% Pt(IV); 76% Pt(0) and 24% Pt(IV); and 65% Pt(0) and 35% Pt(IV), respectively.
Efficiency Enhancement of Methanol/Ethanol Oxidation Reactions on Pt Nanoparticles Prepared Using a New Surfactant, 1,1-Dimethyl Heptanethiol
(Royal Soc Chemistry, 2011) Sen, Fatih; Sen, Selda; Gokagac, Gulsun
In this study, carbon-supported platinum nanoparticle catalysts were prepared using PtCl4 and H2PtCl6 as starting materials and 1-heptanethiol, 1,1-dimethyl heptanethiol, 1-hexadecanethiol and 1-octadecanethiol as surfactants. These nanoparticles can be used as catalysts for methanol and ethanol oxidation reactions in methanol and ethanol fuel cells. 1,1-Dimethyl heptanethiol was used for the first time in this type of synthesis; other surfactants were used to synthesize nanoparticles for comparison of the catalyst's performance. Cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to characterize the catalysts. It should also be stressed that AFM was employed for the first time in determining the surface topography of these catalysts. XRD, TEM and AFM height results indicate that the platinum crystallizes into a face-centered cubic structure and the surfactant plays an important role in determining the size of the platinum nanoparticles. XPS data revealed that the platinum was found in two different oxidation states, Pt(0) and Pt(IV) with a ratio of about 7.5 : 2.5, respectively. Electrochemical studies showed catalyst IIa to be the most active sample towards methanol/ethanol oxidation reactions (similar to 342 A g(-1) Pt at 0.612 V for methanol (4.6 times more active than the commercial catalyst), similar to 309 A g(-1) Pt at 0.66 V for ethanol, (15.4 times more active than the commercial catalyst)).
Platinum Nanocatalysts Prepared With Different Surfactants for C1-C3 Alcohol Oxidations and Their Surface Morphologies by Afm
(Springer, 2012) Ertan, Salih; Sen, Fatih; Sen, Selda; Gokagac, Gulsun
In this study, platinum nanoparticle catalysts have been prepared using PtCl4 as a starting material and 1-octanethiol, 1-decanethiol, 1-dodecanethiol, and 1-hexadecanethiol as surfactants for methanol, ethanol, and 2-propanol oxidation reactions. The structure, particle sizes, and surface morphologies of the catalysts were characterized by X-ray diffraction (XRD), atomic force microscopy and transmission electron microscopy (TEM). XRD and TEM results indicate that all prepared catalysts have a face-centered cubic structure and are homogeneously dispersed on the carbon support with a narrow size distribution (2.0-1.3 nm). X-ray photoelectron spectra of the catalysts were examined and it is found that platinum has two different oxidation states, Pt(0) and Pt(IV), oxygen and sulfur compounds are H2Oads and OHads, bound and unbound thiols. The electrochemical and electrocatalytic properties of these catalysts were investigated with respect to C1-C3 alcohol oxidations by cyclic voltammetry and chronoamperometry. The highest electrocatalytic activity was obtained from catalyst I which was prepared with 1-octanethiol. This may be attributed to a decrease in the ratio of bound to unbound thiol species increase in Pt (0)/Pt(IV), H2Oads/OHads ratios, electrochemical surface area, CO tolerance and percent platinum utility.
The Preparation and Characterization of Nano-Sized Pt-pd/C Catalysts and Comparison of Their Superior Catalytic Activities for Methanol and Ethanol Oxidation
(Springer, 2012) Ozturk, Zafer; Sen, Fatih; Sen, Selda; Gokagac, Gulsun
In this study, two groups of carbon supported PtPd samples with different percentages of metals were prepared to examine the effects of Pd and stabilizing agents on the catalytic activity towards methanol and ethanol oxidation reactions. As a stabilizing agent, 1-hexanethiol and 1,1-dimethyl hexanethiol were used for group "a" and "b" catalysts, respectively. Cyclic voltammetry, chronoamperometry, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS) were employed to understand the nature of the prepared catalysts. TEM and XRD results indicated a similar size distribution of the metal nanoparticles with a narrow average crystallite size of 3.0-3.7 nm. XPS data revealed the presence of two different oxidation states for both platinum and palladium, being Pt(0), Pt(IV), Pd(0), and Pd(II). Electrochemical studies indicated that the group "b" type catalysts have a higher catalytic activity than group "a". The most active catalyst was found to be a carbon supported 88 %Pt/12 %Pd prepared with 1,1-dimethyl hexanethiol, which has an activity of similar to 5 times (similar to 0.450 A/mg Pt at 0.57 V for methanol) and similar to 14 times (similar to 0.350 A/g Pt at 0.56 V for ethanol) greater than the commercial E-TEK catalyst.
The Preparation and Characterization of Nano-Sized Pt-pd/C Catalysts and Comparison of Their Superior Catalytic Activities for Methanol and Ethanol Oxidation (Vol 47, Pg 8134, 2012)
(Springer, 2021) Ozturk, Zafer; Sen, Fatih; Sen, Selda; Gokagac, Gulsun
Preparation and Characterization of Nano-Sized Pt-ru/C Catalysts and Their Superior Catalytic Activities for Methanol and Ethanol Oxidation (Publication With Expression of Concern)
(Royal Soc Chemistry, 2011) Sen, Selda; Sen, Fatih; Gokagac, Gulsun
Carbon-supported PtRu nanoparticles (Ru/Pt: 0.25) were prepared by three different methods; simultaneous reduction of PtCl4 and RuCl3 (catalyst I) and changing the reduction order of PtCl4 and RuCl3 (catalysts II and III) to enhance the performance of the anodic catalysts for methanol and ethanol oxidation. Structure, microstructure and surface characterizations of all the catalysts were carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results of the XRD analysis showed that all catalysts had a face-centered cubic (fcc) structure with different and smaller lattice parameters than that of pure platinum, showing that the Ru incorporates into the Pt fcc structure by different ratios in all the catalysts. The typical particle sizes of all catalysts were in the range of 2-3 nm. The most active and stable catalyst for methanol and ethanol oxidation is catalyst III, in which a large amount (more than 90%) of PtRu alloy formation was observed. It has been found that this catalyst is about 8.0 and 33.4 times more active at similar to 0.60 V towards the methanol and ethanol oxidation reactions, respectively, compared to the commercial Pt catalyst.