• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.407-410
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• 2006

Selection of flow channel in the separation plate of PEMFC is very important parameter to improve its performance and reduce parasite loss. Flow patterns in the channel have great influence on the transport of hydrogen and all and water generated from electrochemical reaction in diffusion layer In this study, fluid flow in flow channel with parallel and interdigitated patterns are simulated three dimensionally on full flow domain including anode and cathode electrode together. The numerical results show that the fuel cell with interdigitated flow channel represents better performance than that with parallel flow channel due to its strong convective transport across the gas diffusion layer. But the pressure drop in parallel flow channel is much more than that in nterdigitated flow channel. The effect of temperature and stoichiometric number on performance can be calculated and analyzed as well.

• Journal of Powder Materials
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• v.20 no.3
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• pp.186-190
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• 2013

The electrochemical performance for the corrosion of zinc anodes according to particle size and shape as anode in Zn/air batteries was study. We prepared five samples of Zn powder with different particle size and morphology. For analysis the particle size of theme, we measured particle size analysis (PSA). As the result, sample (e) had smaller particle size with $10.334{\mu}m$ than others. For measuring the electrochemical performance of them, we measured the cyclic voltammetry and linear polarization in three electrode system (half-cell). For measuring the morphology change of them before and after cyclic voltammetry, we measured Field Emission Scanning Electron Microscope (FE-SEM). From the cyclic voltammetry, as the zinc powder had small size, we knew that it had large diffusion coefficient. From the linear polarization, as the zinc powder had small size, it was a good state with high polarization resistance as anode in Zn/air batteries. From the SEM images, the particle size had increased due to the dendrite formation after cyclic voltammetry. Therefore, the sample (e) with small size would have the best electrochemical performance between these samples.

• Journal of the Korean Institute of Gas
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• v.4 no.1 s.9
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• pp.40-48
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• 2000

A fuel cell is an electrochemical device continuously converting the chemical energy in a fuel and an oxidant to electrical energy by going through an essentially invariant electrode-electrolyte system. Phosphoric acid fuel cell employs concentrated phosphoric acid as an electrolyte. The cell stack in the fuel cell, which is the most important part of the fuel cell system, is made up of anode where oxidation of the fuel occurs cathode where reduction of the oxidant occurs; and electrolyte, to separate the anode and cathode and to conduct the ions between them. Fuel cell performance is associated with many parameters such as operating and design parameters associated with the system configuration. In order to understand the design concepts of the phosphoric fuel cell and predict it's performance, we have here introduced the simulation of the fuel-cell stack which is core component and modeled in a 3-dimensional grid space. The concentration of reactants and products, and the temperature distributions according to the flow rates of an oxidant are computed by the help of a computational fluid dynamic code, i.e., FLUENT.

• Journal of the Korean Electrochemical Society
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• v.12 no.2
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• pp.148-154
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• 2009

With respect to the durability of large scale ($150cm^2$) membrane electrode assembly (MEA) of direct methanol fuel cell (DMFC), degradation phenomena at cathode is monitored and analyzed according to the position on the cathode surface. After constant current mode operation of large scale MEA for 500 hr, the MEA is divided into three parts along the cathode channel; (close to) inlet, middle, and (close to) outlet. The performance of each MEA is tested and it is revealed that the MEA from the cathode outlet of large MEA shows the worst performance. This is due to the catalyst degradation and GDL delamination caused by flooding at cathode outlet of large MEA during the 500 hr operation. Particularly on the catalyst degradation, the loss of electrochemically active surface area (ECSA) of catalyst gets worse along the cathode channel from inlet to outlet, of which the reason is believed to be loss of catalysts by dissolution and migration rather than their agglomeration. The extent of loss in the performance and catalyst degradation has strong relation to the cathode flooding and it is required to develop proper water management techniques and separator channel design to control the flooding.

• Journal of Sensor Science and Technology
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• v.14 no.1
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• pp.33-41
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• 2005

For more convenient electrode-electrolyte interface impedance analysis in biosensor, a stand-alone impedance measurement system is required. In our study, we developed a PC-based portable system to analyze impedance of the electrochemical cell using microprocessor. The devised system consists of signal generator, programmable amplifiers, A/D converter, low pass filter, potentiostat, I/V converter, microprocessor, and PC interface. As a microprocessor, PIC16F877 which has the processing speed of 5 MIPS was used. For data acquisition, the sampling rate at 40 k samples/sec, resolution of 12 bit is used. RS-232 with 115.2 kbps speed is used for the PC communication. The square wave was used as stimuli signal for impedance analysis and voltage-controlled current measurement method of three-electrode-method were adopted. Acquired voltage and current data are calculated to multifrequency impedance signal after Fourier transform. To evaluate the implemented system, we set up the dummy cell as equivalent circuit of which was composed of resistor, parallel circuit of capacitor and resistor connected in parallel and measured the impedance of the dummy cell; the result showed that there exist accuracy within 5 % errors and reproduction within 1 % errors compared to output of Hioki LCR tester and HP impedance analyzer as a standard product. These results imply that it is possible to analyze electrode-electrolyte interface impedance quantitatively in biosensor and to implement the more portable high speed impedance analysis system compared to existing systems.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.10
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• pp.912-917
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• 2007

Many electrochemical power devices such as solid state batteries and solid oxide fuel cell have been studied and developed for solving energy and environmental problems. An amperometric gas sensor usually generates sensing signal of electric current along the proportion of the concentration of target gas under the condition of limiting current. For narrow variations of gas concentration, the amperometric gas sensor can show higher precision than a potentiometric gas sensor does. In additional, cross sensitivities to interfering gases can possibly be mitigated by choosing applied voltage and electrode materials properly. In order to improve the sensitivity to $NO_2$, the device was attached with Au reference electrode to form the amperometric gas sensor device with three electrodes. With the fixed bias voltage being applied between the sensing and counter electrodes, the current between the sensing and reference electrodes was measured as a sensing signal. The response to $NO_2$ gas was obviously enhanced and suppressed with a positive bias, respectively, while the reverse current occurred with a negative bias. The way to enhance the sensitivity of $NO_2$ gas sensor was thus realized. It was shown that the response to $NO_2$ gas could be enhanced sensitivity by changing the bias voltage.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.10
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• pp.667-673
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• 2017

We investigated the temperature uniformity in an anode-supported solid oxide fuel cell, using the open source computational fluid dynamics (CFD) toolbox, OpenFOAM. Numerical simulation was performed in three different flow paths, i.e., co-flow, counter-flow, and cross-flow paths. Gas flow in a porous electrode was calculated using effective diffusivity while considering the effect of interconnect rib. A lumped internal resistance model derived from a semi-empirical correlation was implemented for the calculation of electrochemical reaction. The result showed that the counter-flow path displayed the most uniform temperature distribution.

• Journal of Industrial and Engineering Chemistry
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• v.68
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• pp.161-167
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• 2018

In this study, transition metal coated carbon nanofibers (CNFs) were synthesized and applied as anode materials of Li secondary batteries. CNFs/Ni foam was immersed into 0.01 M transition metal solutions after growing CNFs on Ni foam via chemical vapor deposition (CVD) method. Transition metal coated CNFs/Ni foam was dried in an oven at $80^{\circ}C$. Morphologies, compositions, and crystal quality of CNFs-transition metal composites were characterized by scanning electron microscopy (SEM), Raman spectroscopy (Raman), and X-ray photoelectron spectroscopy (XPS), respectively. Electrochemical characteristics of CNFs-transition metal composites as anodes of Li secondary batteries were investigated using a three-electrode cell. Transition metal/CNFs/Ni foam was directly employed as a working electrode without any binder. Lithium foil was used as both counter and reference electrodes while 1 M $LiClO_4$ was employed as the electrolyte after it was dissolved in a mixture of propylene carbonate:ethylene carbonate (PC:EC) at 1:1 volume ratio. Galvanostatic charge/discharge cycling and cyclic voltammetry measurements were taken at room temperature using a battery tester. In particular, the capacity of the synthesized CNFs-Fe was improved compared to that of CNFs. After 30 cycles, the capacity of CNFs-Fe was increased by 78%. Among four transition metals of Fe, Cu, Co and Ni coated on carbon nanofibers, the retention rate of CNFs-Fe was the highest at 41%. The initial capacity of CNFs-Fe with 670 mAh/g was reduced to 275 mAh/g after 30 cycles.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.134-134
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• 2010

Fuel cell is a device that directly converts chemical energy in the form of a fuel into electrical energy by way of an electrochemical reaction. In the anode for a high temperature fuel cell, nickel or nickel alloy has been used in consideration of the cost, oxidation catalystic ability of hydrogen which is used as fuel, electron conductivity, and high temperature stability in reducing atmosphere. Most MCFC stacks currently operate at an average temperature of $650^{\circ}C$. There is some gains with decreased temperature in MCFC to diminish the electrolyte loss from evaporation and the material corrosion, which could improve the MCFC life. However, operating temperature has a strong related on a number of electrode reaction rates and ohmic losses. Baker et al. reported the effect of temperature (575 to $650^{\circ}C$). The rates of cell voltage loss were 1.4mV/$^{\circ}C$ for a reduction in temperature from 650 to $600^{\circ}C$, and 2.16mV/$^{\circ}C$ for a decrease from 600 to $575^{\circ}C$. The two major contributors responsible for the change in cell voltage with reducing operation temperature are the ohmic polarization and electrode polarization. It appears that in the temperature range of 550 to $650^{\circ}C$, about 1/3 of the total change in cell voltage with decreasing temperature is due to an increase in ohmic polarization, and the electrode polarization at the anode and cathode. In addition, the oxidation reaction of hydrogen on an ordinary nickel alloy anode in MCFC is generally considered to take place in the three phase zone, but anyway the area contributing to this reaction is limited. Therefore, in order to maintain a high performance of the fuel cell, it is necessary to keep this reaction responsible area as wide as possible, that is, it is needed to keep the porosity and specific surface area of the anode at a high level. In this study effective anodes are prepared for low temperature MCFC capable of enhancing the cell performance by using zirconium hydride at least in part of anode material.

• Journal of the Korean Electrochemical Society
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• v.5 no.1
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• pp.7-12
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• 2002

The gas diffusion electrodes as oxygen cathodes f3r the brine electrolysis process were investigated. The gas diffusion electrode consists of a reaction layer, a gas diffusion layer, and a current distributor. The reaction layer was made from hydrophilic carbon black, hydrophobic carbon black, PTFE(polyterafluoroethylene), and Ag catalyst loaded by the silver mirror reaction or impregnation method. The gas diffusion layer was made from hydrophobic carbon black and PTFE, and Ni mesh was used as the current distributor in the reaction layer. The result that the gas diffusion electrode $(10wt\%\;Ag\;catalyst\;and\;20wt\%\;binder)$ manufactured by applying impregnation method to the carbon black f3r reaction layer showed the better performance was obtained from experiments. From the half-cell test, the measured overpotential of this oxygen cathode was about 700mV, And through the electrolysis experiment under the condition of $80^{\circ}C,\;32wt\%$ NaOH, and $300mA/cm^2$, the electrolysis voltage of this electrode was about 2.2 V, The gas diffusion electrodes manufactured in the present research were capable of continuous operations for three months.