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Publication Restricted Carbon aerogel supported pure Pt and bimetallic Pt-Cu alloy nanoparticles by supercritical deposition as electrocatalysts for polymer electrolyte membrane fuel cells(Koç University, 2016) Barım, Şansım Bengisu; Erkey, Can; 0000-0001-6539-7748; Koç University Graduate School of Sciences and Engineering; Chemical and Biological Engineering; 29633Publication Open Access Effect of cerium doping on morphology and physical properties of alpha-Fe2O3 films prepared by hydrothermal electrodeposition(Electrochemical Society (ECS), 2014) Department of Chemistry; Akkaya, Ceren Yılmaz; Ünal, Uğur; PhD Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and EngineeringIn this study, electrochemical growth of Ce-doped alpha-Fe2O3 films is reported. Electrodeposition at 75 degrees C and also a combined hydrothermal-electrochemical method to obtain hematite are presented. Both acidic and neutral plating solutions were used for the depositions. Ferric oxyhydroxide is produced by electrodeposition at 75 degrees C and converted to hematite phase after annealing. Hydrothermal-electrodeposition at 130 degrees C results in formation of hematite phase directly. The effect of temperature, deposition solution and cerium ion amount on the morphology and physical properties of hematite films are characterized.Publication Open Access Electrochemical deposition of Mn:ZnO films under hydrothermal conditions(Electrochemical Society (ECS), 2013) N/A; Department of Chemistry; Akkaya, Ceren Yılmaz; Ünal, Uğur; PhD Student; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of SciencesThis study demonstrated the electrochemical deposition of Mn-doped ZnO films under hydrothermal conditions at 130 degrees C in 50% v/v DMSO-H2O mixture. X-ray diffraction analysis showed that the deposition of the ZnO structures was along (002) direction. However, the presence of Mn2+ affected the thickness of ZnO structures and we believe that the interaction of Mn2+ with the nonpolar surface of ZnO restricts lateral growth. Mn appears in the mixed oxide state in ZnO lattice. The photoluminescence spectra of the films show only UV emission indicating high crystal quality. The blueshift of the UV emission is observed after the introduction of Mn impurity into the ZnO lattice. The surface morphology, lattice structure, Mn content, chemical binding characteristics, and optical properties of the deposits were examined by scanning electron microscopy, X-ray diffraction, X-ray photoelectron-spectroscopy and photoluminescence spectroscopy, respectively.Publication Restricted Electrochemical investigations on functionalized 2D graphene, molybdenum disulfide and nickel sulfide(Koç University, 2022) Solati, Navid; Kaya, Sarp; 0000-0002-2591-5843; Koç University Graduate School of Sciences and Engineering; Materials Science and Engineering; 116541Publication Open Access Evaluating the manufacturing quality of lithium Ion pouch batteries(Institute of Physics (IOP) Publishing, 2022) Kong, Lingxi; Aalund, Ryan; Stoliarov, Stanislav, I.; Pecht, Michael; Alipour, Mohammad; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM)Lithium-ion batteries must undergo a series of quality control tests before being approved for sale. In this study, quality control tests were carried out on two types of lithium-ion pouch batteries, here denoted as type A (with stacked electrode configuration) and type B (with a jelly-roll arrangement) to assess the effectiveness of the tests. Electrochemical tests, which included capacity and impedance measurements, found that both types of batteries met the specifications. However, computed tomography (CT) scan, disassembly, and material characterization revealed quality concerns in battery assembly and material composition. Results showed that, for an A cell, cathode extended past anode at the top and bottom of the roll, and a CT scan revealed inhomogeneities in the electrode near the corners. Similarly, analysis of a B cell revealed gaps in the winding structure and cathode material discrepancies. More specifically, the lithium nickel manganese cobalt oxide (NMC) material specified by the battery manufacturer turned out to be lithium cobalt oxide (LCO). The findings indicate that systematic quality control tests are needed to properly identify defects in batteries before they are used in products.Publication Open Access FR4-based electromagnetic energy harvester for wireless tyre sensor nodes(Elsevier, 2009) Department of Electrical and Electronics Engineering; Hatipoğlu, Gökhan; Ürey, Hakan; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; N/A; 8579An electromagnetic (EM) power generator having 46 Hz resonance frequency is designed to scavenge mechanical vibrations occurring in tyres due to lyre-road contact. The major innovation is the use of FR4 as a structural spring material as well as utilizing a spacer and stopper mechanism increasing the shock resistance by limiting the maximum deflection. The novel magnet assembly and spacer design provide high power density. The tangential acceleration waveforms of typical tyre rotation is used as an input in the experiments and 0.4 mW power is obtained over a 100 Omega load resistance for 15g peak-to-peak amplitude at 22,83 Hz, corresponding to about 150 kph vehicle speed. Maximum acceleration is limited with the shaker, larger power values are expected in actual operation. The performance is obtained off-resonance and superior to resonant Silicon MEMS based scavengers.Publication Open Access Highly sensitive optical sensor for hydrogen gas based on a polymer microcylinder ring resonator(Elsevier, 2020) Eryürek, Mustafa; Department of Physics; Department of Chemistry; Department of Electrical and Electronics Engineering; Bavili, Nima; Balkan, Timuçin; Morova, Berna; Uysallı, Yiğit; Kaya, Sarp; Kiraz, Alper; Researcher; Researcher; PhD Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Department of Electrical and Electronics Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; N/A; N/A; N/A; 116541; 22542A highly sensitive platform is demonstrated for hydrogen gas (H-2) sensing based on a polymer microcylinder ring resonator (PMRR) obtained by an optical fiber coated with an inner nanofilm of amorphous palladium (Pd) and an outer polymer layer of polydimethylsiloxane (PDMS) permeable to H-2. The sensing scheme is based on monitoring the spectral shifts of high-quality optical resonances called whispering gallery modes (WGMs) that propagate in the vicinity of the outer rim of the PDMS layer without being affected by the absorption and scattering losses caused by the Pd nanofilm. WGMs are excited by a single-mode tapered optical fiber evanescently coupled to the PMRR. The observed reversible spectral shifts of the WGMs are induced by changes in the diameter of the PDMS layer caused by expansion or contraction of the Pd nanofilm exposed to varying concentrations of H-2. Maximum spectral shift sensitivity of 140 pm/% H-2, a minimum response time of 95 s, and minimum limit of detection of similar to 60 ppm were measured for sensors prepared with different thicknesses of the amorphous Pd nanofilm and tested in the H-2 concentration range up to 1%, having nitrogen gas (N-2) as a carrier. Experiments were also conducted with Pd nanofilms annealed in air or N-2 atmosphere after the deposition. In both cases, smaller sensitivities were observed due to the formation of larger grains within the film, resulting in slower diffusion and reduced solubility of H in the Pd layer. The impacts of oxygen gas and humidity on sensor performance were also studied.Publication Restricted Mesoporous materials for electrochemical energy conversion(Koç University, 2021) Karakaya, Cüneyt; Kaya, Sarp; 0000-0002-2591-5843; Koç University Graduate School of Sciences and Engineering; Materials Science and Engineering; 116541Publication Restricted Modified layered titanates for enhanced photochemical and photoelectrochemical water splitting(Koç University, 2023) Üstünel, Tuğçe; Kaya, Sarp; 0000-0002-2591-5843; Koç University Graduate School of Sciences and Engineering; Materials Science and Engineering; 116541Publication Restricted N-deposited carbon supported FeNi alloys as electrocatalysts for oxygen evolution reaction(Koç University, 2022) Kınık, Aylin; Ünal, Uğur; 0000-0003-4718-1243; Koç University Graduate School of Sciences and Engineering; Chemistry; 42079