investigating the effect of material properties and electrode microstructure on the performance of solid oxide fuel cell (SOFC) electrodes. During cell fabrication by infiltration, the ion-conducting electrolyte phase is sintered first, followed by the addition of the catalytically active perovskite phase into the pores of the electrolyte. The use of separate sintering steps for the electrolyte and the active phase gives one a high degree of control over the microstructure of both phases, unattainable with traditional fabrication methods. In this thesis, the infiltration approach has been used to conduct a systematic investigation into the factors that govern the performance and stability of solid oxide fuel cell cathodes. As a result, a number of microstructural and material properties, crucial for obtaining high electrode activity, were identified. In particular, the effect of varying the ionic conductivity of the porous electrolyte, the specific surface area of the perovskite as well as the specific surface area of the porous electrolyte, and the effect of solid-state reactions between the two phases were studied and were found to significantly affect performance. The experimental findings agreed well with the predictions of a mathematical model that was developed to describe the electrochemical
The purpose of this research is to improve the performance of proton exchange membrane fuel cell (PEMFC) through two approaches. The first approach is to improve water management by using hydrophobic polymers i.e. fluorinated ethylene propylene (FEP) and polytetrafluoroetilene (PTFE) in the microporous layer (MPL). The second approach is to increase the conductivity properties of membrane electrode assembly (MEA) by using carbon nanotubes in MPL.The research results show that the utilization of 20%FEP in MPL gives better cell performance and durability up to 40 h than that of 20 wt.% PTFE because there is strong bonding between FEP and support layer, and it provides high hydrophobicity property inside the pore of carbon paper. The optimum composition of 50 wt.% MWCNT in MPL gives highest cell performance. The MPL with 50 wt.% SWCNT content gives lowest resistance in MPL which corresponds to an improvement of power density about 70% and 20% relative to, respectively, pure Vulcan and 50 wt.% MWCNT.
chitin cannot be described by simple C-R equivalent parallel circuit. In order to clear the origin of frequency dependence of AC electrical conductivity, we show the relation between the real and imaginary parts obtained from the measured impedance data in Figure 8. As shown in Figure 8, the observed impedance data Z shows the semicircle part and linear parts in the impedance plane. This result indicates that two components are contained in the measured impedance. The almost linear behavior in impedance plane is well known as the contribution of Warburg impedance caused by the double layer capacitance and charge transfer resistance at the interface between the electrode and the specimen . On the other hand, the part of semicircle behavior in impedance plane is also observed. When the specimen is considered by the simple C-R parallel equivalent circuit, the impedance Z can be described by the following equation,
Response time of an electrode is evaluated by measuring the average time required to achieve a potential within ±0.1 mV of the final steady-state potential, upon successive immersion of a series of interested ions, each having a ten-fold difference in concentration. It is notable that the experimental conditions-like the stirring or flow rate, the ionic concentration and composition of the test solution, the concentration and composition of the solution to which the electrode was exposed before experiment measurement was performed, any previous usages or preconditioning of the electrode, and the testing temperature have an effort on the experimental response time of a sensor [37,50]. In this work, 15 s response time was obtained for the proposed electrode when contacting different terazosin solutions from 1.0×10 -5 to 1.0×10 −2 mol L -1 .
A dye sensitized solar cell is one of the solar cells that use organic dyes to achieve photovoltaic properties. DSSCs are regarded as third generation solar cells. The photo electrode, counter electrode, electrolyte, and the dye are the major parts of a dye sensitized solar cell and all these have their own significance in the photovoltaic properties. The counter electrode plays an important role of gathering electrons that are generated at the photo-electrode and delivered through the external circuit, back to the electrolyte. Since the electrolyte is corrosive the counter electrode requires a high reaction rate to reduce the iodine in the electrolyte to an iodide ion. To fabricate the device in a cost effective way the researches turned towards carbon electrodes and conductive polymers. So in the present study we modified the counter electrode using MWCNTs and conducting polymers. Here we used Lawsone, a natural dye for the sensitization of nano crystalline TiO 2 . DSSCs are
Figure 2 shows a schematic drawing of the experimental setup of the designed pH sensors. The EGFET devices connected two differently independent structures, one was a sensing structure containing the surface of the sensitive layer and the other was an n-type MOSFET (FET IC4007) structure (Fuji Semiconductors, Tokyo, Japan). The sensing window of pH sensors was 5 mm × 5 mm en- capsulated using epoxy with a silver wire connected to the gate of the commercially available n-type MOSFET, which was connected to a Keithley 237 current-voltage meter (Keithley Instruments, Inc., Cleveland, OH, USA). It should be noted that the reference electrode voltage was increased from 0 to 3 V and the drain-source voltage (V DS ) was maintained to be constant at 0.3 V while the
both the matrix and the ﬁber are homogeneous and isotropic, (c) the thermal contact resistance between the ﬁber and matrix is negligible, (d) the problem is two-dimensional, and (e) the ﬁbers are arranged in a square periodic array, i.e. they are uniformly distributed in the matrix. The model shown in Fig. 3(a) is a unit cell which represents one-cycle of the periodic structure, so the transverse thermal conductivity of unidirectional composite of circular cylinders was estimated by using this unit cell. The unit cell was divided into 4-node ﬁxed size square elements as shown in Fig. 3(b), so that the FE model obtained from the unit cell became equivalent to that obtained from the microstructure of composites. Under the conditions described above, the microstructure is re- stricted to the model size in the direction of estimation even though it is assumed to spread inﬁnitely in other directions. So, the models which consist of several unit cells as shown in Fig. 4 are considered in this work for evaluating the eﬀect of boundary conditions. When the model consists of several unit cells, multiplying the number of elements per unit cell by the number of unit cells gives the total number of elements in the model. Thus, the number of unit cells represents the size of the model in this study. The analysis conditions are shown in Table 1.
The N-CNTs were simply synthesized utilizing a com- mon laboratorial alcohol burner. Two kinds of N-contained liquid amines, n-propylamine and n-butylamine, were selected as the fuels. The substrate was a pure copper plate sized 15 × 15 mm, which was pretreated by the following process: firstly, the sampling surface of the substrate was mechanically polished to a mirror finish as for preparation of metallographic samples; secondly, a thin nanocrystalline Ni layer was pulse plated upon the surface as the catalyst. The detailed plating process has been described elsewhere . Finally, the plated substrates were inserted into the flames for a cer- tain time and a layer of black materials were produced on the sampling surface of the substrates.
The electrochemical cell with three-electrode configuration which was designed by us has been played an important role for evaluating and monitoring the degradation processes of alloys and protective coatings under molten salt film conditions. It also showed the possibility and some credibility even under molten salt film with thermal cyclic conditions. However, it is difficult to use it under more aggressive thermal conditions because the weakness of ceramic tube used for reference electrode and the deformation of whole electrode setting due to the different thermal expansion that every electrode has. In order to improve the electrochemical cell to be more suitable for measurements under molten salt with more severe thermal cycles, two-electrode configuration electrochemical sell was designed and applied to monitoring the corrosion process of Inconel 600 and aluminide diffusion coating under molten sulfate film with 6 thermal cycles.
A Photo electrochemical Cell (PEC) is a device in which one or both electrodes is a photo responsive Semiconductor (SC) such that the Semiconductor with light of , the band gap of the Semiconductor, results in the flow of current in an external circuit (Aruchamy et al., 1982). The photo effect responsible for the current flow occurs at the Semiconductor/ electrolyte interface in which the light absorption takes place in the Semiconductor to produce excess charge carriers. At the interface, when a Semiconductor whose Femi level (electrochemical potential, ) is brought into contact with an electrolyte whose electrochemical (redox) potential is , an equilibrium of electrochemical potentials of the two phases is established by transfer of electrons across the interface. This leads to a potential Barrier for the further flow of charge carriers. The Semiconductor electronic bands near the surface are bent due to the depletion of majority charge carriers near the surface. The magnitude of the height of the potential Barrier (also the extent of band bending), is equal to the difference in the electrochemical potentials (Fermi levels) of the two phases (Semiconductor and electrolyte) before contact given by:
Early in Cauddle and Farmer’s work, it was found that the average pore size of the electrode material had significant effect on the ion removal performance. Yang et al.  conducted special work on the relationship between electrosorption behaviour and the pore size of carbon. They took the overlapping effect into the model by defining the cut-off pore size as the smallest width that contribute to the electrical double layers. The cut- off pore width for 100 ppm NaF at the voltage of 1.2 V is 0.6 nm. Any pore with a width smaller than 0.6 nm does not hold any ion. Mesosized pores can provide a smaller resistance for the ion transport pathway through the porous carbon  and also a high surface area for the ion adsorption . When pore size is larger than 10 nm, the amount of ions adsorbed remain constant. For the regions between 0.6 and 10 nm, the electrical double layers overlap to some extent resulting in par- tially losing the anion capacity. Macrosized pores can serve as ion-buffering reservoirs guarantees shorter ion diffusion distance, which facilitates the rapid transporta- tion of the ions into the interior of the bulk material . Noked et al.  carried out experiments of ions of different dimensions adsorbed onto carbon electrodes with various porous structures. They found that the ratio between the pore size and the ion size affected the elec- trosorption process significantly. When the ions’ radii approached the pore dimension, the electrical double layer charging process was impeded. They also reported that the rate of double layer charging was not only
Recently the jump relaxation model of Funke 16 has been used to account for the frequency dependence of the conductivity in disordered systems. Funke proposed that in the case of structurally disordered materials, if an ion performs a hop to neighboring vacant sites, there is high probability for that ion to hop back to its previous position (an unsuccessful hop) but if the neighborhood then becomes relaxed with respect to the ion position, the ion stays on the new site, the initial forward hop has proved successful. In the plateau region, the dc conductivity is determined entirely by the successful hops. In the region above the plateau, many hops are unsuccessful and, as the frequency is increased, the proportion of these unsuccessful hops rises; this change in the ratio of successful to unsuccessful hops results in the dispersive conductivity. The predictions of this jump relaxation model apply to the temperature dependence of the ac conductivity: different activation energies being associated with unsuccessful and successful hoping processes.
Transfer coefficients of the two-step electrode reaction in which the first electron transfer is rate determining step can be measured by square-wave voltammetry using cathodic and anodic scan directions. The first direction serves for the characterization of the first charge transfer, while the second electrode reaction can be analyzed by the reverse scan. In the latter case it is better that intermediate is stabilized neither thermodynamically nor kinetically and that the second electron transfer is less than thousand times faster than the first one. The relationships between peak potentials and the logarithm of frequency depend on the transfer coefficients α 1 and α 2 , and not on the products
These organisms will contaminate teat cups and milk lines, and they may impact against the teats of cows milked after those that ate infected, particularly during the reverse flow of milk in the teat cup. The excretion of large numbers of mastitis organisms in milk adds to the total number of bacteria in bulk milk, regardless of the degree of care taken with plant hygiene. In England, Jeffrey and Wilson ( 1987 ) tested 9,066 bulk milk samples, 754 of which had total bacterial counts > 45,000 colony forming units per ml. Of these 754 samples, 330 ( 43.8 % ) had greater numbers of mastitis related bacteria than of spoilage organisms usually associated with inadequately sterilized milking equipment. It was further shown that 44 % of producers who were penalized for total bacterial counts, were penalized as a result of mastitis related bacteria. Of the producers who failed because of these mastitis organisms, 78 % had bulk somatic cell counts < 500,000 per ml and 59 % were < 400,000 cells per ml, thus a lower bulk cell count does not guarantee that subclinical mastitis will not cause problems with the bacterial content of milk. There was a seasonal variation, the penalties being more frequent when the cows were kept indoors and were not grazed on pasture.
analysis of the dynamic phenomena occurring inside the SOFC is required. Therefore, a suitable mathematical model must be established to consider the complicated multi-physic dynamic phenomena occurring inside the fuel cell. Considerable number of research work have been conducted on the SOFC dynamic modeling, aiming to simulate transient phenomena such as load change and start up. Achenbach  analyzed the dynamic operation of a planar solid oxide fuel cell. He examined the transient cell voltage performance due to temperature changes and current density. Gemmen and Johnson  investigated a variety of transient cases, including representative load increase and decrease and system shutdown. Wang et al.  investigated the steady state and transient behavior of a co-flow planar solid oxide fuel cell with the volume-resistance characteristic modeling technique. Xie and Xue  developed an isothermal transient model for button solid oxide fuel cell. The model investigates the transient response of the button cell to the step change of load voltage, oxygen concentration and hydrogen concentration. In two literatures published by present authors, [7, 8] the heat-up and start-up behavior and load change response of a tubular SOFC is studied using a 2D transient numerical model.
prepared using a standard paste method. Stainless steel mesh was used as а current collector. The active mass was prepared by mixing the lithium titanate powder (80% wt), carbon black (15% wt, Timcal, Belgium) and polyvinylidenfluoride (5% wt, Aldrich) predissolved in N- methylpyrrolidone (Aldrich). The mass of active material in the electrode was about 8–10 mg cm -2 . Electrodes were pressed under a pressure of 1,000 kg cm -2 with subsequent vacuum drying at 120 о C. Electrochemical cells were assembled in an argon-filled glove box (“Spectro- systems”, Russia). The 1 М LiPF 6 in a mixture of ethylene
Chapter 4. Methods and Materials This chapter includes individual descriptions of the equipment and processes that were developed in the achievement of the project’s goals. The first section will describe the custom built chamber and the design considerations that dictated its final form. This will be followed by a discussion of the perfusion system and how it was designed to maintain the integrity of the living tissue. Aside from the hardware necessary for maintaining the tissue, the hardware and software needed to provide accurate electrode placement on a micron scale will be described in full. In the subsequent section the technique for optically imaging the tissue sample and specifying recording positions will be detailed. Additionally, the stimulating and recording electrode and amplification system design necessary for returning data that can justify the hypothesis will be outlined. This chapter also outlines the baseline recording tests that were conducted to demonstrate the accuracy of all the hardware and software systems described.