Yazar "Muehlbacher, Marlene" seçeneğine göre listele

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    Electrocatalytic Behavior of Hydrogenated Pd-Metallic Glass Nanofilms: Butler-Volmer, Tafel, and Impedance Analyses
    (Springer, 2020) Sarac, Baran; Karazehir, Tolga; Muehlbacher, Marlene; Sarac, A. Sezai; Eckert, Juergen
    Electrocatalytic activity and sorption behavior of hydrogen in nanosized Pd-Si-(Cu) metallic glass thin film and Pd thin film electrodes sputtered on a Si/SiO2 substrate were investigated by linear sweep voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy. The electrode MG4 (Pd69Si18Cu13) exhibits the best performance with the highest electrocatalytic activity in the hydrogen evolution region with less than half of the Tafel slope of Pd thin film of the same thickness and lowest overpotential at 10 mA cm(-2). A new approach has been adopted by a nonlinear fitting of the entire region of the polarization curve (far- and near-equilibrium cathodic and anodic regions) to the Butler-Volmer model. a parameter is lowest for the MG2 electrode (Pd79Si16Cu5), marking that nonequilibrium conditions change the reaction kinetics. Together with MG2, MG4 shows the lowest Bode magnitude values for hydrogen sorption and evolution regions, indicating that the bonding and release of hydrogen atoms to the electrode is easier. MG4 electrode shows a dramatic decrease of the overpotential after 100 cycles, yielding an increase in hydrogen activity. Besides, MG4 exhibits the sharpest current density drop in the HER region in cyclic voltammetry compared with other MG and Pd electrodes, indicating higher electrocatalytic activity towards hydrogen evolution. The findings highlight the influence of the selected metallic glasses for the design and development of metal catalysts with higher sorption kinetics and/or electrocatalytic turnover.
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    Öğe
    Electrosorption of Hydrogen in Pd-Based Metallic Glass Nanofilms
    (Amer Chemical Soc, 2018) Sarac, Baran; Karazehir, Tolga; Muehlbacher, Marlene; Kaynak, Baris; Gammer, Christoph; Schoeberl, Thomas; Sarac, A. Sezai
    As an efficient potential hydrogen storage and conversion system, hydrogen electrosorption and evolution mechanisms in Pd-based metallic glass thin films (MGTFs) are investigated. In this study, thin films of 55 nm thickness were deposited by dc magnetron sputtering. The amorphous structure of MGTFs and the atomically smooth interface between the MGTF and substrate were confirmed by transmission electron microscopy, whereas the composition-dependent surface roughness was obtained via atomic force microscopy. The shifts in the broad diffraction maxima for the Si and Cu additions were evaluated by X-ray diffraction. The Pd thin film (PdTF) and MGTF working electrodes were chronoamperometrically saturated in 0.5 M H2SO4 solution. The formation of palladium hydride (PdHx) in the MGTFs was investigated by X-ray photoelectron spectroscopy. Cyclic voltammograms were subsequently recorded (between -0.2 and 1.4 V) at sweep rates of 0.02 V s(-1). Electrochemical impedance spectroscopy of MGTFs and PdTF was performed in full spectrum including sorption, desorption, and evolution of hydrogen in a conventional three-electrode configuration. Electrochemical circuit modeling provided the relationship between the composition-dependent hydrogen evolution and H absorption/adsorption processes. The adsorption capacitance parameter Y-ad corresponding to alpha- and beta-hydride formation in the case of Pd0.79Si0.16Cu0.05 MGTF is similar to 5 times higher than that of the crystalline Pd thin film which is in line with the decrease in the charge-transfer resistance R-ct. Addition of Cu disturbs the symmetry of the glass formers, leading to remarkable changes in interfacial hydrogen bonding and diffusion of hydrogen into sublayers. Compared to other Pd-based micron-sized materials, our findings show excellent volumetric hydrogen storage capacity 4 times higher than that of the traditional counterparts of several microns, and 50% higher than the Pd thin films of the same thickness, together with high tunable capacitance, charge-transfer resistance, and diffusivity depending on the glass-forming characteristics of the nanosized MGTF.
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    Öğe
    Nanoporous Pd-Cu-Si Amorphous Thin Films for Electrochemical Hydrogen Storage and Sensing
    (Amer Chemical Soc, 2021) Sarac, Baran; Karazehir, Tolga; Yuce, Eray; Muehlbacher, Marlene; Sarac, A. Sezai; Eckert, Juergen
    Increasing the efficiency of hydrogen storage and release using recent generation metallic glass nanofilms (MGNFs) offers green solutions for nanoscale energy applications. Contrary to flat nanofilms, enhanced electrochemical performance of Pd-Cu-Si MGNF assemblies for hydrogen interaction is obtained on different sizes and configurations of a nanoporous alumina support. In particular, 10 nm thick samples with pore diameters of 25 nm reach a high specific pseudocapacitance per unit mass of 637 F g(-1), which is more than an order of magnitude larger than for flat samples, surpassing the precious metal-based systems in the literature. The same electrode exhibits the highest double-layer capacitance calculated from the equivalent circuit model of the electrochemical impedance spectra, featuring its eligibility for hydrogen nanosensors. A rough and fully coated surface is attained for samples of 250 mu m thickness and above, while smoother and open-pore structures are observed for lower thicknesses, inducing a capillary pressure and turbulent flow effect for the latter case. The comparison of cyclic voltammetry (CV) profiles recorded in the region where hydrogen-metal interactions occur confirms a remarkable desorption charge difference, reaching 2.5 times higher values for the 50 nm thick 25 nm pore diameter than the 40 nm pore diameter and flat electrodes, and lower absolute impedance values near-DC range revealing their highly conductive behavior.