• Korean Chemical Engineering Research
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• v.44 no.6
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• pp.597-601
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• 2006

The degradation of the Nafion membrane by oxygen radical (OH, $HO_2$) was investigated in Polymer electrolyte membrane fuel cell (PEMFC). Nafion membrane was degraded in Fenton solution consisted with hydrogen peroxide (10-30％) and ferrous ion (1-4 ppm) at $80^{\circ}C$. After degradation in Fenton solution, C-F, S-O and C-O chemical bonds of membrane were broken by oxygen radical attack. Breaking of C-F bond reduced the mechanical strength of Nafion membrane, and hence induced pinholes, resulting in increase of $H_2$ crossover through the membrane. Decomposition of S-O and C-O bonds decreased the ion exchange capacity of the electrolyte membrane. The performance of unit cell composed the membrane, which was degraded in 30％ $H_2O_2$ with 4ppm $Fe^{2+}$ solution for 48 hr, was about half times as low as one with normal membrane.

• Membrane Journal
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• v.26 no.2
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• pp.141-145
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• 2016

Polymer electrolyte membranes (PEMs) are key components to determine electrochemical fuel cell performances, in addition to electrode materials. The PEMs need to satisfy selective transport behaviors to small molecules including gases and protons; the PEMs have to transport protons as fast as possible, while they should act as hydrogen barriers, since the permeated gas induces the thermal degradation of cathode catalyst, resulting in rapid electrochemical reduction. To date, limited tools have been used to measure how fast hydrogen gas permeates through PEMs (e.g., Constant volume/variable Pressure (time-lag) method). However, most of the measurements are conducted under vacuum where PEMs are fully dried. Otherwise, the obtained hydrogen permeance is easily changeable, which causes the measurement errors to be large. In this study, hydrogen permeation properties through Nafion212 used as a standard PEM are evaluated using an in-situ measurement system in which both temperature and humidity are controlled at the same time.

• Advances in Energy Research
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• v.2 no.1
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• pp.21-31
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• 2014

The use of a microporous membrane along with Au/C catalyst for direct glycerol alkaline fuel cell was investigated. In comparison with Nafion 112, the microporous Celgard 3401 membrane provides a better cell performance due to the lower ionic resistance as confirmed by impedance spectra. The single cell using Au/C as anode catalyst prepared by using PVA protection techniques provided a higher maximum power density than the single cell with commercial PtRu/C at $18.65mW\;cm^{-2}$ The short-term current decay studies show a better stability of Au/C single cell. The higher activity of Au/C over PtRu/C was owing to the lower activation loss of Awe. The magnitude of current decay indicates a low problem of glycerol crossover from anode to cathode side. The similar performance of single cell with and without humudification at cathode points out an adequate transport of water through the microporous membrane.

• Journal of the Korean Ceramic Society
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• v.29 no.8
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• pp.587-592
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• 1992

Sheets of SiC-SiC whisker maxed matrix were prepared from the mixed slurry of SiC whisker and SiC matrix by the rolling method. With the increase of SiC whisker, the pore size, the porosity and the phosphoric acid absorbency of the matrix were increased, while the bubble pressure was decreased. The activation energy for the transfer of H+ ion was decreased with the increase of mixing ratio of SiC whisker to the SiC matrix from the measurement of hydrogen ion conductivity. The activation energy was evaluated as 0.25 eV when the mixing ratio of SiC whisker to the SiC matrix was 1 : 2 and the activation energy was 0.16 eV for the 2 : 1 matrix. It means that SiC whisker matrix contributes to attain a better microstructure for the diffusion of hydrogen ion. From the measurement of single cell performance of matrix with various mixing ratio, it is concluded that if SiC-SiC whisker maxed matrix has a sufficient bubble pressure to prevent the crossover of H2 gas, the current density of a fuel cell is increased with the increase of acid absorbency of the matrix. Current density was improved from 140 mA/$\textrm{cm}^2$ for 0.25 mm thickness of matrix to 170 mA/$\textrm{cm}^2$ for the 0.20 mm one at 700 mV.

• Applied Chemistry for Engineering
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• v.27 no.2
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• pp.123-127
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• 2016

Methanol fuel cells having advantages of relatively favorable reaction kinetics and higher energy density have attracted increasing interests as best alternative to hydrogen fuel cell because of H2 production, storage and distribution issues. While there have been extensive research works on developing key components such as electrocatalysts as well as their physicochemical properties in practical formic acid fuel cells, there have also been urgent requests for investigating which fuel sources will be more suitable for direct liquid fuel cells in future. In this mini-review, we highlight the overall interest and outlook of formic acid fuel cells in terms of electrocatalysts, fuel supply and crossover, water management, fuel cell efficiency and system integration in comparison with methanol fuel cells.

• Korean Chemical Engineering Research
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• v.55 no.1
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• pp.107-114
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• 2017

The performance of polymer electrolyte membrane fuel cell (PEMFC) could be deteriorated when fuel contains contaminants such as carbon monoxide (CO) or hydrogen sulfide ($H_2S$). Generally, $H_2S$ is introduced in hydrogen by steam reforming of hydrocarbon which has mercaptan as odorant. $H_2S$ poisoning effect on PEMFC performance was examined on this study. Pure hydrogen injection, voltage cycling and water circulation methods were compared as performance recovery methods. The PEMFC performance was analyzed using electrochemical methods such as polarization curve, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Pure hydrogen injection and voltage cycling methods showed low recovery ratio, however, water circulation method showed high recovery ratio over 95%. Because anode was directly poisoned by $H_2S$, anode water circulation showed higher recovery ratio compared to the other methods. Water circulation method was developed to recover PEMFC performance from $H_2S$ poisoning. This method could contribute to PEMFC durability and commercialization.

• Transactions of the Korean hydrogen and new energy society
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• v.16 no.2
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• pp.170-179
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• 2005

Electrolyte loss is considered as one of the major obstacles limiting the life time of molten carbonate fuel cells (MCFCs). Unit cells with an effective area of 100 $cm^2$ were prepared and were operated to determine the optimum matrix thickness which contains the maximum amount of electrolyte without serious preformance loss caused by high resistance. Matrices with different thickness, 1.45, 1.8, and 2.3 mm, were used in unit cells and those cells were operared about 5000, 10000, and 4000 hrs. The unit cell used 1.8 mm thick matrix showed 0.85 V (at 150 mA/$cm^2$) as the intial performance and this cell voltage is not lower than the cell voltage obtained in the cell with 1 mm thick matrix. This cell was operated for 10000 hrs. The cell used 1.45 mm thick matrices showed 16.6 % in the electrolyte loss after 5000 hr operation. In the case of the cell with 2.3 mm thick matrix, the initial cell voltage was below 0.80 V (at 150 mA/$cm^2$). For thermal cycle test, the gas crossover amount of unit cell used 1.8 mm thick matrix was much less than that of the cell with 1.0 mm thick matrix.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.3
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• pp.243-249
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• 2012

A lightweight 200W direct methanol fuel cell (DMFC) stack is designed and fabricated to power a small scale Unmanned Aerial Vehicle (UAV). The DMFC stack consists of 33-cells in which membrane-electrode assemblies (MEAs) having an active area of 88 $cm^2$ are sandwiched with lightweight composite bipolar plates. The total stack weight is around 3.485 kg and stack performance is tested under various methanol feed concentrations. The DMFC stack delivers a maximum power of 248 W at 13.2 V and $71.3^{\circ}C$ under methanol feed concentration of 1.2 M. In addition, the voltage of individual cell in the 33-cell stack is measured at various current levels to ensure the stability of DMFC stack operations. The cell voltage distribution data exhibit the maximum cell voltage deviation of 28 mV at 15 A and hence the uniformity of cell voltages is acceptable. These results clearly demonstrate that DMFC technology becomes a potential candidate for small-scale UAV applications.

• Journal of Pharmacopuncture
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• v.18 no.2
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• pp.7-18
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• 2015

Objectives: Lawsone (1,4 naphthoquinone) is a non redox cycling compound that can be catalyzed by DT diaphorase (DTD) into 1,2,4-trihydroxynaphthalene (THN), which can generate reactive oxygen species by auto oxidation. The purpose of this study was to evaluate the toxicity of the phytomarker 1,4 naphthoquinone and its metabolite THN by using the molecular docking program AutoDock 4. Methods: The 3D structure of ligands such as hydrogen peroxide ($H_2O_2$), nitric oxide synthase (NOS), catalase (CAT), glutathione (GSH), glutathione reductase (GR), glucose 6-phosphate dehydrogenase (G6PDH) and nicotinamide adenine dinucleotide phosphate hydrogen (NADPH) were drawn using hyperchem drawing tools and minimizing the energy of all pdb files with the help of hyperchem by $MM^+$ followed by a semi-empirical (PM3) method. The docking process was studied with ligand molecules to identify suitable dockings at protein binding sites through annealing and genetic simulation algorithms. The program auto dock tools (ADT) was released as an extension suite to the python molecular viewer used to prepare proteins and ligands. Grids centered on active sites were obtained with spacings of $54{\times}55{\times}56$, and a grid spacing of 0.503 was calculated. Comparisons of Global and Local Search Methods in Drug Docking were adopted to determine parameters; a maximum number of 250,000 energy evaluations, a maximum number of generations of 27,000, and mutation and crossover rates of 0.02 and 0.8 were used. The number of docking runs was set to 10. Results: Lawsone and THN can be considered to efficiently bind with NOS, CAT, GSH, GR, G6PDH and NADPH, which has been confirmed through hydrogen bond affinity with the respective amino acids. Conclusion: Naphthoquinone derivatives of lawsone, which can be metabolized into THN by a catalyst DTD, were examined. Lawsone and THN were found to be identically potent molecules for their affinities for selected proteins.

• Korean Chemical Engineering Research
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• v.50 no.5
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• pp.778-782
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• 2012

Until a recent day, degradation of PEMFC MEA (membrane and electrode assembly) has been studied, separated with membrane degradation and electrode degradation, respectively. But membrane and electrode were degraded coincidentally at real PEMFC operation condition. Therefore in this work, AST (Accelerated Stress Test) of MEA degradation was done at the condition that membrane and electrode were degraded simultaneously. There was interaction between membrane degradation and electrode degradation. Membrane degradation reduced the decrease range of catalyst active area by electrode degradation. Electrode degradation reduces increase range of the hydrogen crossover current and FER (Fluoride Emission Rate) by membrane degradation.