• Journal of Powder Materials
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• v.24 no.1
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• pp.24-28
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• 2017

Silicon alloys are considered promising anode active materials to replace Li-ion batteries by graphite powder, because they have a relatively high capacity of up to 4200 mAh/g, and are environmentally friendly and inexpensive ECO-materials. However, its poor charge/discharge properties, induced by cracking during cycles, constitute their most serious problem as anode electrode. In order to solve these problems, Si-Ge-Al alloys with porous structure are designed as anode alloy powders, to improve cycling stability. The alloys are melt-spun to obtain the rapidly solidified ribbons, and then ball-milled to make fine powders. The powders are etched using 1 M HCl solution, which gives the powders a porous structure by removing the element Al. Subsequently, in this study, the microstructures and the characteristics of the etched powders are evaluated for application as anode materials. As a result, the etched porous powder shows better electrochemical properties than as-milled Si-Ge-Al powder.

• Applied Chemistry for Engineering
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• v.33 no.6
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• pp.646-652
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• 2022

The dead-end anode (DEA) system is a method that closes the anode outlet and supplies fuel by pressure. The DEA method could improve fuel usage and power efficiency through system simplification. However, flooding occurs due to water and nitrogen back diffusion from the cathode to the anode during the DEA operation. Flooding is a cause of decreased fuel cell performance and electrode degradation. Therefore, tthe structure and components of polymer electrolyte membrane fuel cell (PEMFC) should be optimized to prevent anode flooding during DEA operation. In this study, the effect of a porous flow field with metal foam on fuel cell performance and fuel efficiency improvement was investigated in the DEA system. As a result, fuel cell performance and purge interval were improved by effective water management with a porous flow field at the cathode, and it was confirmed that cathode flow field structure affects water back-diffusion. On the other hand, the effect of the porous flow field at the anode on fuel cell performance was insignificant. Purge interval was affected by metal foam properties and shown stable performance with large cell size metal foam in the DEA system.

• Korean Journal of Materials Research
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• v.20 no.11
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• pp.592-599
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• 2010

A porous nickel-tin nano-dendritic electrode, for use as the anode in a rechargeable lithium battery, has been prepared by using an electrochemical deposition process. The adjustment of the complexing agent content in the deposition bath enabled the nickel-tin alloys to have specific stoichiometries while the amount of acid, as a dynamic template for micro-porous structure, was limited to a certain amount to prevent its undesirable side reaction with the complexing agent. The ratios of nickel to tin in the electro-deposits were nearly identical to the ratios of nickel ion to tin ion in the deposition bath; the particle changed from spherical to dendritic shape according to the tin content in the deposits. The nickel to tin ratio and the dendritic structure were quite uniform throughout the thickness of the deposits. The resulting nickel-tin alloy was reversibly lithiated and delithiated as an anode in rechargeable lithium battery. Furthermore, the resulting anode showed much more stable cycling performance up to 50 cycles, as compared to that resulting from dense electro-deposit with the same atomic composition and from tin electrodeposit with a similar porous structure. From the results, it is expected that highly-porous nickel-tin alloys presented in this work could provide a promising option for the high performance anode materials for rechargeable lithium batteries.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.1013-1014
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• 2013

• Journal of Powder Materials
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• v.22 no.1
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• pp.15-20
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• 2015

The composite of porous silicon (Si) and amorphous carbon (C) is prepared by pyrolysis of a nano-porous Si + pitch mixture. The nano-porous Si is prepared by mechanical milling of magnesium powder with silicon monoxide (SiO) followed by removal of MgO with hydrochloric acid (etching process). The Brunauer-Emmett-Teller (BET) surface area of porous Si ($64.52m^2g^{-1}$) is much higher than that before etching Si/MgO ($4.28m^2g^{-1}$) which indicates pores are formed in Si after the etching process. Cycling stability is examined for the nano-porous Si + C composite and the result is compared with the composite of nonporous Si + C. The capacity retention of the former composite is 59.6% after 50 charge/discharge cycles while the latter shows only 28.0%. The pores of Si formed after the etching process is believed to accommodate large volumetric change of Si during charging and discharging process.

• Korean Chemical Engineering Research
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• v.54 no.4
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• pp.459-464
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• 2016

In this study, the electrochemical characteristics of porous silicon/carbon composite anode were investigated to improve the cycle stability and rate performance in lithium ion batteries. In this study, the effect of TEOS and $NH_3$ concentration, mixing speed and temperature on particle size of nano silica was investigated using $St{\ddot{o}}ber$ method. Nano porous Si/C composites were prepared by the fabrication processes including the synthesis of nano $SiO_2$, magnesiothermic reduction of nano $SiO_2$ to obtain nano porous Si by HCl etching, and carbonization of phenolic resin. Also the electrochemical performances of nano porous Si/C composites as the anode were performed by constant current charge/discharge test, cyclic voltammetry and impedance tests in the electrolyte of $LiPF_6$ dissolved inorganic solvents (EC:DMC:EMC=1:1:1vol%). It is found that the coin cell using nano porous Si/C composite has the capacity of 2,006 mAh/g and the capacity retention ratio was 55.4% after 40 cycle.

• Carbon letters
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• v.1 no.1
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• pp.27-30
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• 2000

Performance of direct methanol fuel cell using high porous active carbon as an uncatalysed diffusion layer in anode (composite electrode) has been evaluated. Effects of porous active carbon in anode were investigated by galvanostatic method and Fourier Transform Infrared spectroscopy. The single cell was operated with 2.5 M methanol at temperature of $80-120^{\circ}C$ and showed performance of $210-510\;mA/cm^2$ at 0.4V. By replacing conventional electrode with composite electrode, the increment of $290\;mA/cm^2$ in current density was obtained at $90^{\circ}C$and 0.4V. The potential decay of the single cell was about 14.5% for 20 days operation.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.4
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• pp.353-363
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• 2012

The relationship between the diffusivity and electrochemical characteristics of lithium secondary battery with the modified Si anode material prepared in HF/$AgNO_3$ solution was investigated. The crystallographic structure and images of the modified porous Si and modified Si/Cu was examined using the X-ray diffraction, BET and SEM. To examine the effect of metal composite and pore size distribution according to chemical etching on the electrochemical characterization, the electrodes for half cells were prepared with the modified Si, modified Si/Cu, and modified Si/Cu annealed with $600^{\circ}C$. Our results showed that the chemical diffusivity of lithium ions was related to structure and resistance of Si/Cu composite anode material. The lithium diffusivity in modified silicon compound calculated from the CV was at the range of $1{\times}10^{-12}$ to $9{\times}10^{-16}cm^2/s$. The effects of modified silicon structure and resistance on the cycling efficiency were significant.

• Journal of the Korean institute of surface engineering
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• v.26 no.6
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• pp.291-298
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• 1993

In order to substitute for porous nickel anode in Molten Carbonate Fuel Cell(MCFC), porous cermet elec-trode was fabricated with Ni and Ni-P coated ceramic powder. Ni and Ni-P were coated by electroless plat-ing method in the nickel solution containing of hydrazine and sodium hypophosphate as a reducing agent. The plating solution was stirred by air and mechanical agitator. Ultrasonic irradiation was applied to the plating bath to improved the effect of agitation and coating speed. Electorde was formed by pressing method and doc-tor blade method followed by sinterd at$ 800^{\circ}C$ for 6 hours in H2 environment. Anode performance test carried out by potentiodynamic polarization technique in the MCFC operating condition and 154-161mA/$\textrm{cm}^2$ as ob-tained as a anode current density at the+100mV overpotential.

• Journal of the Korean Electrochemical Society
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• v.16 no.3
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• pp.138-144
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• 2013

Electrochemical reductions of $UO_2$ at various anode-to-cathode distances (1.3, 2.3, 3.2, 3.7 and 5.8 cm) were carried out to investigate the effect of the anode-to-cathode distance on the electrochemical reduction rate. The geometry of the electrolysis cell in this study, apart from the anode-to-cathode distance, was identical for all of the electrolysis runs. Porous $UO_2$ pellets were electrolyzed by controlling a constant cell voltage in molten $Li_2O-LiCl$ at $650^{\circ}C$. A steel basket containing the porous $UO_2$ pellets and a platinum plate were used as the cathode and anode, respectively. The metallic products were characterized by means of a thermogravimetric analyzer, an X-ray diffractometer and a scanning electron microscope. The electrolysis runs conducted during this study revealed that a short anode-to-cathode distance is advantageous to achieve a high current density and accelerate the electrochemical reduction process.