• Journal of Hydrogen and New Energy
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• 제13권2호
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• pp.143-150
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• 2002

The thermal behavior of $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$ prepared by a co-precipitation wasinvestigated for Hz generation by the thermochemical cycle. The reduction reaction of $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$ started from $480^{\circ}C$, and the weight loss was 1.6 wt% up to $1100^{\circ}C$. At this reaction, $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$ was reduced by release of oxygen bonded with the $Fe^{3+}$ ion in the B site of ($CO_{0.5}$ $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$. In the $H_2O$ decomposition reaction, $H_2$ was generated by oxidationof reduced $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$. The crystal structure of $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$ for reduction reaction maintained spinel structure and the lattice constant of $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$ ($8.41\AA$) was enlarged to $8.45\AA$. But the lattice constant of $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$ after $H_2O$ decomposition reaction did not change to $8.45\AA$. Then, $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$ is excellent material in the thermochemical cyclic reaction due to release oxygen at low temperature for the reduction reaction and produce $H_2$ maintaining crystal structure for redox reaction.

• Journal of Hydrogen and New Energy
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• 제19권6호
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• pp.505-513
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• 2008

The two-step thermochemical cycle was examined on the $CeO_2$, YSZ, and $ZrO_2$-supported $NiFe_2O_4$ to investigate the effects of support material addition. The supported $NiFe_2O_4$ was prepared by the aerial oxidation method. Thermal reduction was conducted at 1573K and 1523K while water-splitting was carried out at 1073K. Supporting $NiFe_2O_4$ on $CeO_2$, YSZ and $ZrO_2$ alleviated the high-temperature sintering of iron-oxide. As a result, the supported $NiFe_2O_4$ exhibited greater reactivity and repeatability in the water-splitting cycle as compared to the unsupported $NiFe_2O_4$. Especially, $ZrO_2$-supported $NiFe_2O_4$ showed better sintering inhibition effect than other supporting materials, but hydrogen production amount was decreased as cycle repeated. In case of $CeO_2$-supported $NiFe_2O_4$, improvement of hydrogen production was found when the thermal reduction was conducted at 1573K. It was deduced that redox reaction of $CeO_2$ activated above 1573K.

• Journal of Energy Engineering
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• 제15권2호
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• pp.107-117
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• 2006

The status of water splitting thermochemical cycle for hydrogen production was reviewed in this article. Mass production of hydrogen could be possible using the thermochemical process which is similar to the concept of conventional chemical reaction system if the high temperature heat source is available. The mediators (chemicals and reagents) should be used to split chemically stable water, and should be recycled in a closed cycle in order to be environmentally acceptable. Though there is no process to reach commercial stage, IS cycle, two-step cycles based on metallic oxide such as ZnO/Zn, $Fe_3O_4/FeO$ and the associated cycles are attracted due to their possibilities of application. Development of materials for high temperature and/or corrosive conditions during thermochemical process is still important topic in some thermochemical processes.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.163.2-163.2
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• 2010

We developed a simple method to synthesis a nitrogen doped graphene, nitrogen plasma treated graphene (NPG) sheets thought nitrogen plasma etching of graphene oxide (GO). X-ray photo electron spectroscopy (XPS) study of NPG sheets treated at various plasma conditions reveal that N-doping is classified to 3 kinds of binding configurations. The nitrogen doping concentration is at least 1.5 at % and up to 3 at% with changing of ratio of nitrogen configuration in NPG. Our group demonstrate ultracapacitor with high capacity and extremely durable using a NPG sheets that are comparable to pristine graphene supercapacitor, and pseudocapacitor using polymer and metal oxide with redox reaction, capacitance that are three-times higher, and a cycle life that are extremely stable. We also realized flexible capacitor by using the paper electrode that are coated by NPG sheets. NPG paper capacitor presented almost same performance compare with NPG on a metal substrate, and durability is much more enhanced than that. To additionally explain that how different kind of atoms in graphene layers can act as the ion absorption sites, we simulated the binding energy between nitrogen in graphene layer and ions in electrolyte. Increasing the energy density and long cycle life of ultracapacitor will enable them to compete with batteries and conventional capacitors in number of applications.

• Journal of the Korean Society of Industry Convergence
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• 제19권4호
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• pp.176-184
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• 2016

Electrochemical ion exchange method is expected to be one of the most acceptable techniques for the separation of radioactive cations from nuclear wastewater. In this study a thin film of hexacyanoferrate on nickel surface was derivatized chemically in an aqueous potassium-ferricyanide solution. Electrochemical redox behavior of the nickel hexacyanoferrate(NiHCNFe) film electrode was investigated with the use of cyclic voltammetry potentiostated from -100 to 800 mV versus SCE. The electro-reduction characteristics of the NiHCNFe film were examined in the cobalt solutions. The NiHCNFe ion exchanger was more useful at lower concentration, lower temperature, and pH7 of the cobalt solution. The capacity loss of NiHCNFe was 0.018%/cycle that was less than the average loss of 2~3%/cycle of the convective organic exchanger. The 45~55% of the initial cobalt ions was electro-deposited on the NiHCNFe by using continuous recirculating reactor system. As a result, it was found that the electroactive NiHCNFe films showed better performance than the organic resins for the separation of cobalt ion from the aqueous solutions.

• Korean Chemical Engineering Research
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• 제57권6호
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• pp.868-873
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• 2019

In this study, the evaluation of performance of AORFB using methyl viologen and TEMPOL as organic active materials in neutral supporting electrolyte (NaCl) with various membrane types was performed. Using methyl viologen and TEMPOL as active materials in neutral electrolyte solution, the cell voltage is 1.37V which is relatively high value for AORFB. Two types of membranes were examined for performance comparison. First, when using Nafion 117 membrane which is commercial cation exchange membrane, only the charge process occurred in the first cycle and the single cell couldn't work because of its high resistance. However, when using Fumasep anion exchange membrane (FAA-3-50) instead of Nafion 117 membrane, the result was obtained as the totally different charge-discharge graphs. When current density was $40mA{\cdot}cm^{-2}$ and cut off voltage range was from 0.55 V to 1.7 V, the charge efficiency (CE) was 97% and voltage efficiency (VE) was 78%. In addition, the discharge capacity was $1.44Ah{\cdot}L^{-1}$ which was 54% of theoretical capacity ($2.68Ah{\cdot}L^{-1}$) at $10^{th}$ cycle and the capacity loss rate was $0.0015Ah{\cdot}L^{-1}$ per cycle during 50 cycles. Through cyclic voltammetry test, it seems that this difference in the performance between the full cell using Nafion 117 membrane and Fumasep anion exchange membrane came from increasing resistance due to chemical reaction between membrane and active material, not the capacity loss due to cross-over of active material through membrane.

• Bulletin of the Korean Chemical Society
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• 제27권9호
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• pp.1381-1385
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• 2006

Cobalt (cyclam) complex has been successfully immobilized onto SBA-15, and proven to be an active catalyst for the epoxidation of styrene with tert-butyl hydroperoxide as a terminal oxidant. The selectivity for styrene oxide was observed to be up to 66% with 40% styrene conversion after 12h reaction time. The reversible redox cycle between Co(III) and Co(II) couple which was supposed to play key role during the epoxidation reaction was supported by a cyclic voltametry analysis. The textural properties of the catalyst was characterized by XRD, N2 adsorption-desorption, and TEM analysis.

• Carbon letters
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• 제19권
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• pp.40-46
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• 2016

Nitrogen-atom doped graphene oxide was considered to prevent the dissolution of polysulfide and to guarantee the enhanced redox reaction of sulfur for good cycle performance of lithium sulfur cells. In this study, we used urea as a nitrogen source due to its low cost and easy preparation. To find the optimum urea content, we tested three different ratios of urea to graphene oxide. The morphology of the composites was examined by field emission scanning electron microscope. Functional groups and bonding characterization were measured by X-ray photoelectron spectroscopy. Electrochemical properties were characterized by cyclic voltammetry in an organic electrolyte solution. Compared with thermally reduced graphene/sulfur (S) composite, nitrogen-doped graphene/S composites showed higher electroactivity and more stable capacity retention.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 한국환경과학회 2004년도 봄 학술발표회 발표논문집
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• pp.40-45
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• 2004

액상 TCE 제거반응을 위한 Hetero-CWO 촉매들 중에서 $CoO_{x}$/$TiO_2$와 $CuO_{x}$/$TiO_2$가 상대적으로 유망한 것으로 보여졌으며, 특히 5% $CoO_{x}$/$TiO_2$ 촉매의 경우에 반응시간에 따른 활성추이는 TCE 제거반응에서 주요 역할을 할 수 있는 반응 활성점의 변화를 암시하고 있다. $FeO_{x}$ /$TiO_2$와 Fe-MFI 촉매상에서 TCE 제거반응에 대한 시간에 따른 활성거동으로부터 활성점의 redox cycle를 어떻게 제어하는가 하는 점이 매우 중요함을 알 수 있었으며, 촉매표면에서 이를 유지.증진시킬 수 있는 촉매 디자인 기법이 요구되었다.

• BMB Reports
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• 제44권7호
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• pp.423-434
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• 2011

A female hormone, estrogen, is linked to breast cancer incidence. Estrogens undergo phase I and II metabolism by which they are biotransformed into genotoxic catechol estrogen metabolites and conjugate metabolites are produced for excretion or accumulation. The molecular mechanisms underlying estrogen-mediated mammary carcinogenesis remain unclear. Cell proliferation through activation of estrogen receptor (ER) by its agonist ligands and is clearly considered as one of carcinogenic mechanisms. Recent studies have proposed that reactive oxygen species generated from estrogen or estrogen metabolites are attributed to genotoxic effects and signal transduction through influencing redox sensitive transcription factors resulting in cell transformation, cell cycle, migration, and invasion of the breast cancer. Conjuguation metabolic pathway is thought to protect cells from genotoxic and cytotoxic effects by catechol estrogen metabolites. However, methoxylated catechol estrogens have been shown to induce ER-mediated signaling pathways, implying that conjugation is not a simply detoxification pathway. Dual action of catechol estrogen metabolites in mammary carcinogenesis as the ER-signaling molecules and chemical carcinogen will be discussed in this review.