Researcher:
Karakaya, Cüneyt

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PhD Student

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Cüneyt

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Karakaya

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Karakaya, Cüneyt

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2020 - 20233

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Researcher Of Publications: search.filters.isAuthorOfPublication.af8de69d-ea6a-4d05-9528-0665c30e08d8

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    Controlling oxygen reduction reaction activities of Ag@Pt core-shell nanoparticles via tuning of ag in the surface layer
    (Wiley-VCH, 2023) Savaci, Umut; Turan, Servet; N/A; N/A; N/A; Department of Chemistry; Department of Chemistry; Aksoy, Dilan; Karakaya, Cüneyt; Balkan, Timuçin; Metin, Önder; Kaya, Sarp; PhD Student; PhD Student; Other; Faculty Member; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; College of Sciences; College of Sciences; N/A; N/A; N/A; 46962; 116541
    Herein, the effect of Pt shell thickness and Ag content in the surface layer on the oxygen reduction reaction activities of Ag@Pt core@shell nanoparticles (NPs) is discussed. Ag@Pt NPs are synthesized via the seeded-growth method, where colloidal Ag NPs are first synthesized and used as seeds for the growth of Pt. Electrochemical activity measurements in alkaline media show a remarkable dependency between the Ag content in the shell and the oxygen reduction reaction (ORR) activity, where the overpotentials required for -1.0 mA cm(-2) drop gradually, that is, 0.72, 0.77, and 0.80 V-RHE for Ag@Pt-25, Ag@Pt-35, and Ag@Pt-45, respectively. Tafel analysis also confirms this dependency with 73.5 mV dec(-1) for Ag@Pt-25, 71.3 mV dec(-1) for Ag@Pt-35, and 68.8 mV dec(-1) for Ag@Pt-45. A combination of the high-resolution transmission electron microscope, X-ray photoelectron spectroscopy, and X-Ray diffraction analysis shows an increase of the Pt shell thickness. It is shown that the absence of Pt-H adsorption/desorption peaks in cyclic voltammetry of Ag@Pt NPs is correlated with Ag in the surface layer, which plays an important role in the ORR activity due to the blockage of Pt(111) terrace sites. Rate-limiting first-electron transfer to oxygen is facilitated by decreasing Ag amount at the surface.
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    Mesoporous molybdenum sulfide-oxide composite thin-film electrodes prepared by a soft templating method for the hydrogen evolution reaction
    (American Chemical Society (ACS), 2022) Savaç, Umut; Keleş, Emre; Turan, Servet; N/A; N/A; N/A; Department of Chemistry; Karakaya, Cüneyt; Solati, Navid; Balkan, Timuçin; Kaya, Sarp; PhD Student; PhD Student; Other; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; College of Sciences; N/A; N/A; N/A; 116541
    Electrode designs involving binder-free nanoparticles integrated within interconnected pore networks are critical in scaling up electrolyzers. MoS2 is the most promising electrocatalyst candidate that can show hydrogen evolution reaction (HER) activity comparable to platinum (Pt). Herein, a facile one-step soft templating method was developed to synthesize mesoporous molybdenum sulfide-oxide composite thin-film electrocatalysts directly on any substrate without using a binder or a template. Fabricated electrocatalysts contain amorphous MoS3 and small crystallite-sized MoS2 embedded into amorphous MoO3 with a large surface area (around 182 m(2)/g). The electrocatalyst layer undergoes in situ electrochemical activation in which amorphous MoS3 is reduced to MoS2 during the HER in acidic media. The electrocatalyst layer on the carbon fiber exhibits a low overpotential (similar to 189 mV at 10 mA/cm(2)) and Tafel slope (53 mV/dec) toward the HER after electrochemical activation.
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    Advancing the understanding of the structure-activity-durability relation of 2D MoS2 for the hydrogen evolution reaction
    (Amer Chemical Soc) N/A; N/A; Department of Chemistry; Solati, Navid; Karakaya, Cüneyt; Kaya, Sarp; PhD Student; PhD Student; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 116541
    It has been decades since electrochemical water splitting was proposed as a promising strategy for renewable hydrogen production. Transition-metal dichalcogenides offer cheap, earth-abundant catalyst candidates for the hydrogen evolution reaction (HER). Among those, molybdenum disulfide (MoS2) has been the subject of a vast number of studies, where different approaches such as manipulating the type and number of layers, or density of the intrinsic active sites, and engineering compositional phase and structure have been employed to enhance the electrochemical activity. Herein, we show the HER activities of twodimensional 1T-and 1H-MoS2 mixed phases with respect to the pure 1H-MoS2 scale with the 1T phase. The creation of S vacancies in 1H-MoS2 enhances HER activities. Further enhancement in the activity is achieved by N doping induced by N2 plasma exposure owing to the formation of a metallic 1T phase and S vacancies. The spectroelectrochemical Raman spectroscopy and ex-situ X-ray photoelectron spectroscopy investigations reveal a gradual phase conversion induced by H adsorption during electrochemical tests. The 1T to 1H phase transformation results in a significant loss in HER activity.
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    Mesoporous thin-film NIS2 as an idealized pre-electrocatalyst for a hydrogen evolution reaction
    (Amer Chemical Soc, 2020) Savacı, Umut; Kele, Emre; Turan, Servet; Çelebi, Serdar; N/A; N/A; Department of Chemistry; Solati, Navid; Karakaya, Cüneyt; Kaya, Sarp; PhD Student; PhD Student; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 116542
    Developing active, durable, and inexpensive electrocatalysts is critical for hydrogen production to meet ever-growing sustainable energy needs. Nickel sulfides offer significant potential as electrocatalysts for a hydrogen evolution reaction (HER); however, the active phase governing the electrochemical conversion is still under debate. We show that mesoporous thin-film NiS2 synthesized by a novel soft-templating method without post-sulfurization exhibits superior HER activity in alkaline media after a preconditioning step that results in sulfur leaching, amorphization of the surface, and collapse of the mesoporous structure. A comparative analysis with crystalline NiS2 reveals that partial hydroxylation of the under-coordinated Ni sites is responsible for the superior HER activity.