Vibration of simply-supported trapezoidal plates II. Unsymmetric trapezoids

This paper deals with the investigation of the vibration characteristics of simply-supported unsymmetric trapezoidal plates. For numerical calculations, the relationship between the eigenvalue problems of a polygonal simply-supported plate and polygonal membrane is again effectively utilized. The Galerkin method is applied, with the deflection surface expressed in terms of a Fourier sine series in transformed coordinates. Numerical values for the first seven to eight frequencies for different geometries of the unsymmetric trapezoid are presented in the form of tables. Also the nodal patterns for a few representative configurations are presented.

A Durable PEFC with Carbon-Supported Pt-TiO2 Cathode: A Cause and Effect Study

Durability is central to the commercialization of polymer electrolyte fuel cells (PEFCs). The incorporation of TiO2 with platinum (Pt) ameliorates both the stability and catalytic activity of cathodes in relation to pristine Pt cathodes currently being used in PEFCs. PEFC cathodes comprising carbon-supported Pt-TiO2 (Pt-TiO2/C) exhibit higher durability in relation to Pt/C cathodes as evidenced by cell polarization, impedance, and cyclic voltammetry data. The degradation in performance of the Pt-TiO2/C cathodes is 10% after 5000 test cycles as against 28% for Pt/C cathodes. These data are in conformity with the electrochemical surface area and impedance values. Pt-TiO2/C cathodes can withstand even 10,000 test cycles with nominal effect on their performance. X-ray diffraction, transmission electron microscope, and cross-sectional field-emission-scanning electron microscope studies on the catalytic electrodes reflect that incorporating TiO2 with Pt helps in mitigating the aggregation of Pt particles and protects the Nafion membrane against peroxide radicals formed during the cathodic reduction of oxygen. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3421970] All rights reserved.

Pd Supported on Titanium Nitride for Efficient Ethanol Oxidation

The excellent metal support interaction between palladium (Pd) and titanium nitride (TiN) is exploited in designing an efficient anode material. Pd-TN, that could be useful for direct ethanol fuel cell in alkaline media. The physicochemical and electrochemical characterization of the Pd-TiN/electrolyte interface reveals an efficient oxidation of ethanol coupled with excellent stability of the catalyst under electrochemical conditions. Characterization of the interface using in situ Fourier transform infrared spectroscopy (in situ FITR) shows the production CO2 at low overvoltages revealing an efficient cleaving of the C-C bond. The performance comparison of Pd supported on TiN (Pd-TiN) with that supported on carbon (Pd-C) clearly demonstrates the advantages of TiN support over carbon. A positive chemical shift of Pd (3d) binding energy confirms the existence of metal support interaction between pd and TiN, which in turn helps weaken the Pd-CO synergetic bonding interaction. The remarkable ability of TiN to accumulate -OH species on its surface coupled with the strong adhesion of Pd makes TiN an active support material for electrocatalysts.

Platinum particles supported on titanium nitride: an efficient electrode material for the oxidation of methanol in alkaline media

In the present study, titanium nitride which shows exceptional stability, extreme corrosion resistance, good electronic conductivity and adhesion behaviour is used to support platinum particles and then used for methanol oxidation in an alkaline medium. The catalyst shows very good CO tolerance for the electrochemical oxidation of methanol. In situ infrared spectroelectrochemical data show the remarkable ability of TiN to decompose water at low over potentials leading to -OH type functional groups on its surface which in turn help in alleviating the carbon monoxide poisoning associated with methanol oxidation. TiN supported catalysts are found to be very good in terms of long term stability, exchange current density and stable currents at low over voltages. Supporting evidence from X-ray photoelectron spectroscopic data and cyclic voltammetry clearly demonstrates the usefulness of TiN supported Pt catalysts for efficient methanol oxidation in alkaline media.

Tuning the interfacial properties of supported metal nanoclusters

Nanoclusters are objects made up of several to thousands of atoms and form a transitional state of matter between single atoms and bulk materials. Due to their large surface-to-volume ratio, nanoclusters exhibit exciting and yet poorly studied size dependent properties. When deposited directly on bare metal surfaces, the interaction of the cluster with the substrate leads to alteration of the cluster properties, making it less or even non-functional. Surfaces modified with self-assembled monolayers (SAMs) were shown to form an interesting alternative platform, because of the possibility to control wettability by decreasing the surface reactivity and to add functionalities to pre-formed nanoclusters. In this thesis, the underlying size effects and the influence of the nanocluster environment are investigated. The emphasis is on the structural and magnetic properties of nanoclusters and their interaction with thiol SAMs. We report, for the first time, a ferromagnetic-like spin-glass behaviour of uncapped nanosized Au islands tens of nanometres in size. The flattening kinetics of the nanocluster deposition on thiol SAMs are shown to be mediated mainly by the thiol terminal group, as well as the deposition energy and the particle size distribution. On the other hand, a new mechanism for the penetration of the deposited nanoclusters through the monolayers is presented, which is fundamentally different from those reported for atom deposition on alkanethiols. The impinging cluster is shown to compress the thiol layer against the Au surface and subsequently intercalate at the thiol-Au interface. The compressed thiols try then to straighten and push the cluster away from the surface. Depending on the cluster size, this restoring force may or may not enable a covalent cluster-surface bond formation, giving rise to various cluster-surface binding patterns. Compression and straightening of the thiol molecules pinpoint the elastic nature of the SAMs, which has been investigated in this thesis using nanoindentation. The nanoindenation method has been applied to SAMs of varied tail groups, giving insight into the mechanical properties of thiol modified metal surfaces.

Synergitic Promotion of Electrooxidation of Methanol of Carbon-Supported PT-SN Catalysts

Electrooxidation of methanol in sulphuric acid on carbon-supported electrodes containing Pt-Sn bimetal catalysts prepared by an in-situ route is reported, The catalysts have been characterized employing chemical analyses, XRD, and XANES data in conjunction with electrochemistry. This study suggests that the Sn content in Pt-Sn bimetals produces: (i) a charge transfer from Sn to Pt and (ii) an increase in the coverage of adsorbed methanolic residues with the Sn content. From the electrode-kinetics data, it is inferred that while the electrodes of (3:3) Pt-Sn/C catalyst involve a 2-electron rate-limiting step akin to Pt/C electrodes, it is shifted to only 1-electron on (3:2) Pt-Sn/C, (3:3) Pt-Sn/C, and (3:4) Pt-Sn/C electrodes.

Methanol oxidation on carbon-supported platinum-tin electrodes in sulfuric acid

A study is made of the electrooxidation of methanol in sulfuric acid on carbon-supported electrodes containing platinum-tin bimetal catalysts that are prepared by an in situ potentiometric-characterization route. The catalysts are investigated by employing chemical analyses, X-ray diffraction (XRD), X-ray absorption-near-edge spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS) data in conjunction with electrochemical measurements. From the electrochemical data, it is inferred that while an electrode with (3:1) Pt-Sn/C catalyst involves a two-electron rate-limiting step akin to platinum-on-carbon electrodes, it is shifted to a one-electron mechanism on electrodes with (3:2)Pt-Sn/C, (3:3)Pt-Sn/C, and (3:4)Pt-Sn/C catalysts. The study suggests that the tin content in the platinum-tin bimetal catalyst produces: (i) a charge transfer from tin to platinum; (ii) an increase in the coverage of adsorbed methanolic residues with increase in the tin content, as indicated by the shift in rest potential of the electrodes towards the reversible value for oxidation of methanol (0.043 V versus SHE), and (iii) a decrease in the overall content of higher valent platinum sites in the catalyst.

Methanol oxidation on carbon-supported Pt---Sn electrodes in silicotungstic acid

Electro-oxidation of methanol was studied on carbon-supported Pt---Sn/C electrodes in silcotungstic acid (SiWA) at various concentrations. The porous-carbon electrodes employing Pt---Sn/C catalyst have been characterized using chemical analyses, X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) in conjunction with electrochemistry. The presence of Pt---Sn and Pt3Sn alloys along with Pt and SnO2 phases in the catalyst were identified by XRD. XPS analysis showed a lower amount of PtO species in the Pt---Sn/C catalyst with respect to the corresponding Pt/C sample. From the steady-state galvanostatic polarization data on Pt---Sn/C electrodes in SiWA, it is inferred that a one-electron process is the rate determining step. The performance of the electrodes in 0.084 M SiWA was better than in 2.5 M H2SO4 under similar conditions up to load currents of about 100 mA cm−2 indicating the promoting behaviour of the electrolyte. At currents larger than 100 mA cm−2, the performance of the electrodes in 0.084 SiWA was poorer than that in 2.5 M H2SO4 mainly due to the dominance of mass polarization in the former owing to the large size of keggin units associated with the structure of SiWA. This aspect was supported by cyclic voltammetry and ac impedance studies on Pt---Sn/C electrodes. Simulation of the electrochemical impedance response for the oxidation of methanol in SiWA was carried out using the equivalent electrical circuit model.

Methanol oxidation on carbon-supported platinum-tin electrodes in sulfuric acid

A study is made of the electrooxidation of methanol in sulfuric acid on carbon-supported electrodes containing platinum-tin bimetal catalysts that are prepared by an in situ potentiometric-characterization route. The catalysts are investigated by employing chemical analyses, X-ray diffraction (XRD), X-ray absorption-near-edge spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS) data in conjunction with electrochemical measurements. From the electrochemical data, it is inferred that while an electrode with (3:1) Pt-Sn/C catalyst involves a two-electron rate-limiting step akin to platinum-on-carbon electrodes, it is shifted to a one-electron mechanism on electrodes with (3:2)Pt-Sn/C, (3:3)Pt-Sn/C, and (3:4)Pt-Sn/C catalysts. The study suggests that the tin content in the platinum-tin bimetal catalyst produces: (i) a charge transfer from tin to platinum; (ii) an increase in the coverage of adsorbed methanolic residues with increase in the tin content, as indicated by the shift in rest potential of the electrodes towards the reversible value for oxidation of methanol (0.043 V versus SHE), and (iii) a decrease in the overall content of higher valent platinum sites in the catalyst.

Methanol oxidation on carbon-supported Pt---Sn electrodes in silicotungstic acid

Electro-oxidation of methanol was studied on carbon-supported Pt-Sn/C electrodes in silcotungstic acid (SiWA) at various concentrations. The porous-carbon electrodes employing Pt-Sn/C catalyst have been characterized using chemical analyses, X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) in conjunction with electrochemistry. The presence of Pt-Sn and Pt3Sn alloys along with Pt and SnO2 phases in the catalyst were identified by XRD. XPS analysis showed a lower amount of PtO species in the Pt-Sn/C catalyst with respect to the corresponding Pt/C sample. From the steady-state galvanostatic polarization data on Pt-Sn/C electrodes in SiWA, it is inferred that a one-electron process is the rate determining step. The performance of the electrodes in 0.084 M SiWA was better than in 2.5 M H2SO4 under similar conditions up to load currents of about 100 mA cm-2 indicating the promoting behaviour of the electrolyte. At currents larger than 100 mA cm-2, the performance of the electrodes in 0.084 SiWA was poorer than that in 2.5M H2SO4 mainly due to the dominance of mass polarization in the former owing to the large size of Keggin units associated with the structure of SiWA. This aspect was supported by cyclic voltammetry and ac impedance studies on Pt-Sn/C electrodes. Simulation of the electrochemical impedance response for the oxidation of methanol in SiWA was carried out using the equivalent electrical circuit model.

Design and development of a self-supported polymer electrolyte fuel cell system with anodic dead-end operation

Design and operational details for a self-supported polymer electrolyte fuel cell (PEFC) system with anodic dead-end fuel supply and internally humidified cathodic oxidant flow are described. During the PEFC operation, nitrogen and water back diffuse across the Nafion membrane from the cathode to the anode and accumulate in the anode flow channels affecting stack performance. The accumulated inert species are flushed from the stack by purging the fuel cell stack with a timer-activated purge valve to address the aforesaid problem. To minimize the system complexity, stack is designed in such a way that all the inert species accumulate in only one cell called the purge cell. A pulsed purge sequence comprises opening the valve for purge duration followed by purge-valve closing for the hold period and repeating the sequence in cycles. Since self-humidification is inadequate to keep the membrane wet, the anodic dead-end-operated PEFC stack with composite membrane comprising perflourosulphonic acid (Nafion) and silica is employed for keeping the membrane humidified even while operating the stack with dry hydrogen and internally humidified air.

Linear dynamics and active control of an elastically supported travelling string

In this paper, the linear dynamics and active control of a string travelling with uniform velocity is presented. Discrete elastic supports are introduced along the length of the string. Finite element formulation is adopted to obtain the governing equations of motion. The velocity of translation introduces gyroscopic terms in the system equations. The effect of translation and the discrete elastic supports on the free vibration solution is studied. The solution is utilized in actively controlling the string vibrations due to an initial disturbance. The control, affected in modal space, is optimal with respect to a quadratic performance index. Numerical results are presented to demonstrate the effectiveness of the control strategy in regulating the travelling string vibrations.

Methanol electrooxidation on carbon-supported Pt-WO3−x electrodes in sulphuric acid electrolyte

Electrooxidation of methanol has been studied in sulphuric acid electrolyte at 60 degrees C on carbon-supported Pt-WO3-x, electrodes employing varying amounts of WO3-x,. It is found that the electrodes containing (3:1) Pt-WO3-x, composite catalyst exhibit a higher catalytic activity towards methanol electrooxidation than platinized carbon electrodes without WO3-x. In the light of the XPS and XRD data on the carbon-supported (3:1) Pt-WOx sample, it is speculated that the WOx is present in the form of an oxyhydroxide, which can promote surface oxy-species on platinum by proton transfer.