Researcher:
Kaya, Sarp

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Sarp

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Kaya

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Kaya, Sarp

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2013 - 2019192020 - 202325

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Now showing 1 - 10 of 45
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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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    Hybrid cufe-cofe Prussian blue catalysts on BIVO4 for enhanced charge separation and injection for photoelectrochemical water oxidation
    (American Chemical Society (ACS), 2022) Vishlaghi, Mahsa Barzgar; Akbari, Sina Sadigh; Karadas, Ferdi; Department of Chemistry; N/A; N/A; Kaya, Sarp; Usman, Emre; Barzgarvishlaghi, Mahsa; Faculty Member; Master Student; PhD Student; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); College of Sciences; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 116541; N/A; N/A
    The utilization of cocatalysts on the photoelectrode surface is a feasible strategy to achieve a high photocurrent density in the photoelectrochemical water oxidation process. The catalysts can enhance the activity by improving the reaction kinetics, retarding charge carrier recombination, or accumulating charge carriers. In this work, we have utilized a CuFe-CoFe Prussian blue (PB) catalyst layer on the BiVO4 photoanode surface to enhance its water oxidation activity. The hybrid catalyst, in which the semiprecious cobalt ions are partially substituted with earth-abundant copper ions, exhibits 56% higher photocurrent density than the CoFe PB-modified BiVO4. We show that photogenerated hole accumulation is present in the CuFe PB layer, which results in higher charge extraction from the BiVO4 surface. The CoFe PB layer on top of the CuFe one facilitates the charge transfer due to its catalytic activity toward the oxygen evolution reaction (OER).
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    Surfactant-free synthesis of CdS nanorods for efficient reduction of carcinogenic Cr(VI)
    (Taylor and Francis Ltd, 2021) Butler, Ian S.; Rehman, Zia Ur; N/A; N/A; Department of Chemistry; Ullah, Haseeb; Balkan, Timuçin; Kaya, Sarp; Researcher; Other; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); N/A; N/A; College of Sciences; N/A; N/A; 116541
    Hexavalent chromium, Cr(VI), is a toxic, mutagenic and carcinogenic species. We report here the semiconductor-based, photocatalytic reduction of Cr(VI) to trivalent chromium, Cr(III), using CdS nanorods (NRs) as the photocatalyst under visible light illumination. The CdS NRs were synthesized by a facile and scalable solvothermal method in which ethylenediamine acts as solvent and morphology controller. The CdS NRs produced were studied by PXRD, Raman, FESEM, EDX, XPS, PL, UV-visible DRS and BET techniques in order to investigate their structural, morphological and optical properties, as well as their porosity. The photoreduction of Cr(VI) to Cr(III) under visible light illumination was performed under a variety of conditions, i.e., varying the irradiation time, pH, substrate concentration, and the amount of photocatalyst. The maximum photoreduction of Cr(VI) to Cr(III) (99%) was achieved using 60 min of irradiation under acidic conditions (pH 4). The excellent photoreduction ability of the CdS NRs can be attributed to their rod-like structure together with their small particle size, large surface area, and clean surfaces. These properties enhanced separation of the photo-generated electron-hole pairs, which was confirmed by the XRD, BET, and PL measurements. In addition, the results of a kinetic study indicated that the photoreduction of Cr(VI) to Cr(III) follows a pseudo-first-order kinetic model. A possible mechanism for the photocatalytic reduction of Cr(VI) to Cr(III) is also proposed in this paper.
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    Strong light–matter interactions in Au plasmonic nanoantennas coupled with Prussian blue catalyst on BiVO4 for photoelectrochemical water splitting
    (Wiley-VCH Verlag, 2020) Ghobadi, T. Gamze Ulusoy; Ghobadi, Amir; Soydan, Mahmut Can; Karadas, Ferdi; Ozbay, Ekmel; N/A; Department of Chemistry; Kaya, Sarp; Barzgarvishlaghi, Mahsa; Faculty Member; PhD Student; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); College of Sciences; Graduate School of Sciences and Engineering; 116541; N/A
    Invited for this month′s cover is the group of Ferdi Karadas and Ekmel Ozbay at Bilkent University. The image proposes a hybrid architecture, in which the semiconductor photoactive host is coupled to a plasmonic particle and a catalyst, to significantly substantiate the photoactivity of the cell.
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    Enhanced electron transport induced by a ferroelectric field in efficient halide perovskite solar cells
    (Elsevier, 2020) Askari, Masoud; Halali, Mohammad; Department of Chemistry; N/A; N/A; Department of Chemistry; Zarenezhad, Hamaneh; Solati, Navid; Balkan, Timuçin; Kaya, Sarp; Researcher; PhD Student; Other; Faculty Member; Department of Chemistry; N/A; N/A; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); N/A; College of Sciences; Graduate School of Sciences and Engineering; N/A; College of Sciences; N/A; N/A; N/A; 116541
    Perovskite solar cells have been appearing as a superior photovoltaic device owing to their high photovoltaic performance and low cost of fabrication. The formation of a compact and uniform perovskite layer with large crystal size is a significant factor to get the best device performance. In this work, polyvinylidene difluoride (PVDF) was used as a ferroelectric polymer additive to fabricate high-performance mesoporous CH3NH3PbI3-xClx mixed-halide perovskite solar cells in a sequential deposition method. Power conversion efficiency has been enhanced from 10.4 to 16.51% in an ambient atmosphere in the presence of an optimized amount of PVDF assuring continuous and smooth layers with large grain size. Besides morphological improvements, this progress in the photovoltaic performance is attributed to the dipole field exerted by PVDF that leads to enhanced charge separation. Further improvements in efficiency (18.60%) have been achieved by directing the dipoles under an external field.
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    Electrocatalytic reduction of CO2 to produce higher alcohols
    (Royal Soc Chemistry, 2018) N/A; N/A; N/A; Department of Chemistry; Munir, Shamsa; Varzeghani, Amir Rahimi; Kaya, Sarp; Researcher; PhD Student; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); N/A; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 116541
    Electrodeposited and thermally oxidized copper surfaces have been documented in recent years to produce simple alcohols. In this work, we endeavored to study the electrochemical reduction of CO2 at different electrodes prepared via the electrodeposition method, namely, Cu-Cu2O, Cu-Cu2O-ZnO, and Cu-ZnO. In addition, thermally oxidized Cu (Cu-TO) was also investigated. C1, C2, and C3 species were produced on Cu-Cu2O-ZnO, Cu-Cu2O, and Cu-ZnO. The highest faradaic efficiency (FE of 97.4%) of the liquid products (methanol, formate, n-propanol, acetone) was evidenced on Cu-ZnO. The formation of C3 species with high FE on the Cu-ZnO electrode is attributed to the fast C-C-C coupling at the Cu-Zn interface. on thermally oxidized Cu, the total FE of the liquid products (methanol, formate, ethanol, acetate, n-propanol) was found to be 58.51%, which is considerably closer to the already reported values for these electrodes. Moreover, the Cu-Cu2O-ZnO electrode revealed selectivity toward methanol production. Detailed morphological and elemental analyses of the electrode, performed using XPS, Raman spectroscopy, and FESEM, as well as activity measurements to obtain an insight into the mechanistic pathways, reveal that C-C coupling is favored on Cu-0 sites rather than Cu2O. Moreover, methanol formation seems to proceed via O coordination of CO2 to Cu-Cu2O surface having (100) facets, whereas C coordination is favored on Cu-TO with (111) exposed faces, resulting in Cu-0 sites. The localized formation of ZnO nanoflowers was observed on Cu-ZnO electrodes after the electrochemical reduction of CO2, which is attributed to the mechanistic pathway involving chemical steps, leading to the formation of C3 species.
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    Easy hydrogenation and dehydrogenation of a hybrid graphene and hexagonal boron nitride monolayer on platinum
    (Institute of Physics (IOP) Publishing, 2021) Pis, Igor; Nappini, Silvia; Magnano, Elena; Bondino, Federica; N/A; Department of Chemistry; N/A; Panahi, Mohammad; Kaya, Sarp; Kahraman, Abdullah; PhD Student; Faculty Member; PhD Student; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; College of Sciences; Graduate School of Sciences and Engineering; N/A; 116541; N/A
    Understanding the fundamental steps of adsorption and controlled release of hydrogen in two-dimensional (2D) materials is of relevance for applications in nanoelectronics requiring tuning the physical properties or functionalization of the material, hydrogen storage and environmental sensors. Most applications demand that hydrogen adsorption and desorption can be controlled at room temperature. Here we report an element-specific study on the hydrogenation and dehydrogenation, in a low coverage regime, of a quasi-free standing 2D heterostructure (h-BNG) in the form of coexisting lateral domains of isostructural hexagonal boron nitride (h-BN) and graphene (Gr) on Pt(111). At very low hydrogen coverage a selective and partial hydrogenation of the Gr domains is observed in h-BNG. At the same time no changes are detected in the h-BN domains, indicating a preferential hydrogenation of Gr rather than h-BN domains. At higher coverage, hydrogenation of both Gr and h-BN domains is detected. A thermally facile hydrogen release from h-BN domains near room temperature is observed. Furthermore, the hybrid h-BNG 2D heterostructure enables also a much easier H-2 thermal release from Gr domains when compared with a full Gr monolayer grown on the same Pt(111) substrate. These results suggest that the presence of coexisting hydrogenated h-BN domains could destabilize C-H bonds in Gr.
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    Operando x-ray photoelectron spectroscopy studies of aqueous electrocatalytic systems
    (Springer, 2016) Ogasawara, Hirohito; Nilsson, Anders; Department of Chemistry; Kaya, Sarp; Faculty Member; Department of Chemistry; College of Sciences; 116541
    Development of efficient fuel cell and electrochemical cell devices to retrieve energy in a renewable manner lies in the molecular level understanding of the conversion processes taking place at surfaces and interfaces. These processes involve complicated bond breaking and formation at the surfaces as well as charge transfer through interfaces which are challenging to track under operational conditions. We address the nature of these interfacial processes using ambient pressure X-ray photoelectron spectroscopy by leveraging both its chemical and surface sensitivity. Herein, we give several examples of fuel cell and electrolysis reactions to demonstrate the importance of probing the surface under operating conditions. Oxygen reduction reaction taking place on the platinum cathode in proton exchange membrane fuel cells, water splitting reactions including oxygen evolution reaction over IrO2 and hydrogen evolution reaction over MoSx reveal that different species dominate on the surface under different operational conditions and surface activities are directly related to the stabilities of those intermediate species and possible structural rearrangements of the catalyst material.
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    A comprehensive study on the characteristic spectroscopic features of nitrogen doped graphene
    (Elsevier, 2019) Ogasawara, Hirohito; N/A; N/A; N/A; Department of Chemistry; Solati, Navid; Mobassem, Sonia; Kahraman, Abdullah; Kaya, Sarp; PhD Student; PhD Student; PhD Student; Faculty Member; Department of Chemistry; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 116541
    Despite significant methodical improvements in the synthesis of N-doped graphene, there are still unsolved questions regarding the control of content and the configuration of nitrogen species in graphene honeycomb network. A cross-examination of X-ray photoelectron spectroscopy and Raman spectroscopy findings indicates that the nitrogen dopant amount is graphene thicknesses dependent, but the various nitrogen dopant coordination can be obtained on both double- and few-layer graphene. Characteristic defect features (D') appearing in Raman spectra upon N-doping is sensitive to nitrogen dopant coordination, graphitic-pyridinic/nitrilic species and therefore the doping level can be identified. Pyridinic and nitrilic nitrogen as primary species turn graphene to p-type semiconductor after a mild thermal treatment.
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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.