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Article Citation - WoS: 44Citation - Scopus: 52Graphene-Supported Platinum Catalyst-Based Membrane Electrode Assembly for Pem Fuel Cell(Springer, 2016) Devrim, Yilser; Albostan, AyhanThe aim of this study is the preparation and characterization of a graphene-supported platinum (Pt) catalyst for proton exchange membrane fuel cell (PEMFC) applications. The graphene-supported Pt catalysts were prepared by chemical reduction of graphene and chloroplatinic acid (H2PtCl6) in ethylene glycol. X-ray powder diffraction, thermogravimetric analysis (TGA) and scanning electron microscopy have been used to analyze structure and surface morphology of the graphene-supported catalyst. The TGA results showed that the Pt loading of the graphene-supported catalyst was 31%. The proof of the Pt particles on the support surfaces was also verified by energy-dispersive x-ray spectroscopy analysis. The commercial carbon-supported catalyst and prepared Pt/graphene catalysts were used as both anode and cathode electrodes for PEMFC at ambient pressure and 70 degrees C. The maximum power density was obtained for the Pt/graphene-based membrane electrode assembly (MEA) with H-2/O-2 reactant gases as 0.925 W cm(2). The maximum current density of the Pt/graphene-based MEA can reach 1.267 and 0.43 A/cm(2) at 0.6 V with H-2/O-2 and H-2/air, respectively. The MEA prepared by the Pt/graphene catalyst shows good stability in long-term PEMFC durability tests. The PEMFC cell voltage was maintained at 0.6 V without apparent voltage drop when operated at 0.43 A/cm(2) constant current density and 70 degrees C for 400 h. As a result, PEMFC performance was found to be superlative for the graphene-supported Pt catalyst compared with the Pt/C commercial catalyst. The results indicate the graphene-supported Pt catalyst could be utilized as the electrocatalyst for PEMFC applications.Article Citation - WoS: 7Citation - Scopus: 9Reliability-Based Evaluation of Hybrid Wind-Solar Energy System(Sage Publications Ltd, 2021) Devrim, Yilser; Eryilmaz, SerkanIn this article, a hybrid system that consists of a specified number of wind turbines and solar modules is considered. In particular, the system is modeled using weightedk-out-of-nsystem which is also known as a threshold system in reliability literature. The system under concern consists ofn1identical wind turbines andn2identical solar modules, and each turbine and module can be in one of two states as working or failed. The probability that the entire hybrid system withn=n1+n2components produces power at minimum levelkis computed and evaluated. The importance of single-wind turbine and solar module is also calculated to measure which renewable energy component is more critical and important. Extensive numerical results that are based on real data set are presented to illustrate the model.Article Citation - WoS: 30Citation - Scopus: 34Preparation and Testing of Nafion/Titanium Dioxide Nanocomposite Membrane Electrode Assembly by Ultrasonic Coating Technique(Wiley-blackwell, 2014) Devrim, Yilser; Alemdaroğlu Temel, Mine; Alemdaroğlu Temel, MineMembrane electrode assemblies with Nafion/nanosize titanium dioxide (TiO2) composite membranes were manufactured with a novel ultrasonic-spray technique (UST) and tested in proton exchange membrane fuel cell (PEMFC). The structures of the membranes were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis. The composite membranes gained good thermal resistance with insertion of TiO2. The SEM and XRD techniques have proved the uniform and homogeneous distribution of TiO2 and the consequent enhancement of crystalline character of these membranes. The existence of nanometer size TiO2 has improved the thermal resistance, water uptake, and proton conductivity of composite membranes. Gas diffusion electrodes were fabricated by UST. Catalyst loading was 0.4 (mg Pt) cm(-2) for both anode and cathode sides. The membranes were tested in a single cell with a 5 cm(2) active area operating at the temperature range of 70 degrees C to 110 degrees C and in humidified under 50% relative humidity (RH) conditions. Single PEMFC tests performed at different operating temperatures indicated that Nafion/TiO2 composite membrane is more stable and also performed better than Nafion membranes. The results show that Nafion/TiO2 is a promising membrane material for possible use in PEMFC at higher temperature. (c) 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40541.Article Citation - WoS: 8Citation - Scopus: 10Computing Reliability Indices of a Wind Power System Via Markov Chain Modelling of Wind Speed(Sage Publications Ltd, 2024) Eryilmaz, Serkan; Bulanik, Irem; Devrim, YilserStatistical modelling of wind speed is of great importance in the evaluation of wind farm performance and power production. Various models have been proposed in the literature depending on the corresponding time scale. For hourly observed wind speed data, the dependence among successive wind speed values is inevitable. Such a dependence has been well modelled by Markov chains. In this paper, the use of Markov chains for modelling wind speed data is discussed in the context of the previously proposed likelihood ratio test. The main steps for Markov chain based modelling methodology of wind speed are presented and the limiting distribution of the Markov chain is utilized to compute wind speed probabilities. The computational formulas for reliability indices of a wind farm consisting of a specified number of wind turbines are presented through the limiting distribution of a Markov chain. A case study that is based on real data set is also presented.
