• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.399-402
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• 2006

현재까지 연료전지 전해질 막으로는 Nafion으로 잘 알려져 있는 perfluorosulfonic acid(PFSA)막이 주를 이루고 있다. 이 막들은 $80^{\circ}C$ 이하의 낮은 온도의 연료전지에서 가장 좋은 성능을 보인다. PFSA 막들은 탄소-불소로 이루어진 사슬의 특성상 산화, 환원의 조건에서도 뛰어난 안정성을 보이며 이온 전도도가 0.1S/cm 이상으로 기존에 알려진 전해질 막들 중 가장 우수한 성능을 나타낸다. 하지만 연료전지의 작동온도가 $100^{\circ}C$ 이상의 높은 온도에서 는 막에 존재하던 수분이 제거되면서 수소이온 전도도가 떨어지며 기계적 물성도 떨어지는 문제점을나타낸다. $100^{\circ}C$ 이상의 온도에서 연료전지를 작동시키면 양쪽의 전극에서 일어나는 촉매반응의 속도가 향상되며, 물의 끓는점 이상에서 작동되므로, 전지 내에서 다양한 상을 고려하지 않고 기화된 물만을 고려하여 설계를 할 수가 있다. 따라서 최근 이러한 고온/저가습 운전을 위 한 전해질 막의 개발을 위해 기존의 Nafion 막에 전도성 무기 입자를 도입하는 연구들이 활발히 진행되고 있다. 본 연구에서는 전도성 무기 입자로서 $ZrO_2$나노입자를 합성하고, 이를 상용 10 wt.% Nafion 용액에 분산하여 solution casting 방법을 통해 $61{\mu}m$ 두께의 유기-무기 복합막을 제조하였다. 제조한 유기-무기 복합막의 성능 평가를 위하여 함수율, 이온 전도도, 당량무게 및 단위 전지를 이용한 전류-전압 곡선을 측정하여 상용 Nafion 112 막과 비교해 보았다. $ZrO_2$ 입자는 전도성이며 동시에 친수성을 나타내기 때문에 상용 막에 비하여 함수율 및 수소이온 전도도가 우수하게 나타났다. 복합막의 이러한 물성은 $100^{\circ}C$이상의 고온에서 전해질 막 내의 물 관리를 용이하게 한다. 단위 전지 운전 온도 $130^{\circ}C$, 상대습도 37%의 운전 조건에서도 상당히 우수한 전지 성능을 보임에 따라 고온/저가습 조건에서 상용 Nafion 112 막보다 우수한 막 특성을 나타냄을 확인하였다.

• Journal of Powder Materials
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• v.21 no.1
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• pp.28-33
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• 2014

This paper describes the surface modification effect of a Ti substrate for improved dispersibility of the catalytic metal. Etching of a pure titanium substrate was conducted in 50% $H_2SO_4$, $50^{\circ}C$ for 1 h-12 h to observe the surface roughness as a function of the etching time. At 1 h, the grain boundaries were obvious and the crystal grains were distinguishable. The grain surface showed micro-porosities owing to the formation of micro-pits less than $1{\mu}m$ in diameter. The depths of the grain boundary and micro-pits appear to increase with etching time. After synthesizing the catalytic metal and growing the carbon nano tube (CNT) on Ti substrate with varying surface roughness, the distribution trends of the catalytic metal and grown CNT on Ti substrate are discussed from a micro-structural perspective.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.445.2-445.2
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• 2014

표면 조직화의 목적은 태양전지 표면에서의 입사되는 빛의 반사율을 감소 시키고, 웨이퍼 내에서 빛의 통과 길이를 길게 하며, 흡수되는 빛의 양을 증가시키는 것이다. 본 연구에서는 여러 가지 표면 조직화 공정 기술을 이용하여 표면 형상에 따른 광 변환 효율에 대해 연구하였으며, 셀을 제작하여 전기적 특성과 광학적 특성의 상관관계를 분석하였다. KOH를 이용한 표면 조직화, 산 증기를 이용한 표면 조직화, 반응성 이온 식각을 이용한 표면 조직화, 금속 촉매 반응을 이용한 표면 조직화 공정 기술을 이용하여 표면 조직화 공정을 진행하였다. 셀 제작 결과, 반사도 결과와는 상반되는 결과를 얻을 수 있었다. 표면 조직화 형상에 따른 셀 효율의 변화는 도핑 프로파일과 표면 재결합 속도의 변화 때문이라 생각되며 더 명확한 분석을 위해 양자 효율을 측정하여 분석을 시도하였다. 표면 조직화 공정 기술별 도핑 프로파일을 보면 KOH를 이용한 표면 조직화 공정을 제외한 나머지 표면 조직화 공정들의 도핑 프로파일은 불균일하게 형성되어 있는 것을 확인 할 수 있다. 양자 효율 측정 결과 단파장 대역에서 낮은 응답특성을 가지는 것을 확인 할 수 있었다. 그 이유는 낮은 반사도를 가지는 표면 조직화 공정의 경우 나노사이즈의 구조를 갖기 때문에 균일한 도핑 프로파일을 얻지 못해 전자, 정공의 분리가 제대로 이루어지지 못하였고 표면 재결합 속도증가의 원인으로 단락전류와 개방전압이 낮아져 효율이 떨어진 것으로 판단된다. 결과적으로 낮은 반사율을 갖는 표면 조직화 공정도 중요하지만 표면 조직화 공정 기술에 따른 균일한 도핑 프로파일을 갖는 공정을 개발한다면 단파장 응답도가 향상되어 단락전류밀도와 개방전압 상승효과를 얻을 수 있을 것이라 판단된다.

• Korean Journal of Materials Research
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• v.21 no.8
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• pp.419-424
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• 2011

Pt nanoparticle catalysts incorporated on $RuO_2$ nanowire support were successfully synthesized and their electrochemical properties, such as methanol electro-oxidation and electrochemically active surface (EAS) area, were demonstrated for direct methanol fuel cells (DMFCs). After fabricating $RuO_2$ nanowire support via an electrospinning method, two different types of incorporated Pt nanoparticle electrocatalysts were prepared using a precipitation method via the reaction with $NaBH_4$ as a reducing agent. One electrocatalyst was 20 wt% Pt/$RuO_2$, and the other was 40 wt% Pt/$RuO_2$. The structural and electrochemical properties of the Pt nanoparticle electrocatalysts incorporated on electrospun $RuO_2$ nanowire support were investigated using a bright field transmission electron microscopy (bright field TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry. The bright field TEM, XRD, and XPS results indicate that Pt nanoparticle electrocatalysts with sizes of approximately 2-4 nm were well incorporated on the electrospun $RuO_2$ nanowire support with a diameter of approximately 50 nm. The cyclic voltammetry results showed that the Pt nanoparticle catalysts incorporated on the electrospun $RuO_2$ nanowire support give superior catalytic activity in the methanol electro-oxidation and a higher electrochemically active surface (EAS) area when compared with the electrospun Pt nanowire electrocatalysts without the $RuO_2$ nanowire support. Therefore, the Pt nanoparticle catalysts incorporated on the electrospun $RuO_2$ nanowire support could be a promising electrode for direct methanol fuel cells (DMFCs).

• Korean Chemical Engineering Research
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• v.44 no.4
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• pp.399-403
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• 2006

There has been numerous reports for the synthesis of mesoporous $TiO_2$ thin films due to not only the high surface area and regular mesoscale pores but also wide band gap and photo activity. However, the synthesis has been restricted by the limited reproducibility mainly due to the extraordinarily fast hydrolysis and condensation rate of titania precursors. In this report, molar composition of reaction batch (HCl/Ti and Ti/P123) and exterior condition (humidity and temperature) during coating and anealing process. Thereafter, the mesoporous $TiO_2$ thin films were characterized by XRD and TEM

• Analytical Science and Technology
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• v.23 no.6
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• pp.560-565
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• 2010

Perchlorate ion ($ClO_4^-$) has been widely used as oxidizing agent in military weapon system such as rocket and missile fuel propellant. So it has been challenging to remove the pollutant of perchlorate ion. nanoscale zero valence iron (nZVI) particles are widely employing reduction catalyst for decomposition of perchlorate ion. nZVI particles has increasingly been utilized in groundwater purification and waste water treatment. But it have strong tendency of aggregation, rapid sedimentation and limited mobility. In this study, we focused on reduction of perchlorate ion using nZVI particles immobilized in alginate polymer bead for stabilization. The stabilized nZVI particles displayed much greater surface area, and much faster reaction rates of reduction of perchlorate ion. In this study, an efficient way to immobilize nZVI particles in a support material, alginate bead, was developed by using $Ca^{2+}$ as the cross-linking cations. The efficiency and reusability of the immobilized Fe-alginate beads on the reduction of perchlorate was tested at various temperature conditions.

• Journal of the Korean Ceramic Society
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• v.45 no.6
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• pp.331-335
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• 2008

The purpose of this study is to characterize the photo-catalytic efficiency of $TiO_2$ nanotube with respect to the distribution of anatase phase which can be changed by the annealing temperature of $TiO_2$ nanotube. $TiO_2$ nanotube was fabricated by the anodization method in the 0.5 wt% HF electrolyte. And then the $TiO_2$ nanotube was annealed at temperatures ranging from $380^{\circ}C$ to $780^{\circ}C$ in dry oxygen ambient for 2 h. For the photo-catalytic water-splitting tests, the photocurrent density was measured as a function of applied potential with a potentiostat using a Ag/AgCl reference, Pt counter electrode, and 1 M KOH electrolyte under illumination of UV by a Xe arc lamp of 1 KW. According to the UV photo-catalytic water-splitting tests, the nanotube annealed at $560^{\circ}C$ was found to show the highest photocurrent density.

• Korean Journal of Materials Research
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• v.19 no.5
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• pp.233-239
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• 2009

The electrocatalytic behavior of the PtCo catalyst supported on the multi-walled carbon nanotubes (MWNTs) has been evaluated and compared with commercial Pt/C catalyst in a polymer electrolyte membrane fuel cell(PEMFC). A PtCo/MWNTs electrocatalyst with a Pt:Co atomic ratio of 79:21 was synthesized and applied to a cathode of PEMFC. The structure and morphology of the synthesized PtCo/MWNTs electrocatalysts were characterized by X-ray diffraction and transmission electron microscopy. As a result of the X-ray studies, the crystal structure of a PtCo particle was determined to be a face-centered cubic(FCC) that was the same as the platinum structure. The particle size of PtCo in PtCo/MWNTs and Pt in Pt/C were 2.0 nm and 2.7 nm, respectively, which were calculated by Scherrer's formula from X-ray diffraction data. As a result we concluded that the specific surface activity of PtCo/MWNTs is superior to Pt/C's activity because of its smaller particle size. From the electrochemical impedance measurement, the membrane electrode assembly(MEA) fabricated with PtCo/MWNTs showed smaller anodic and cathodic activation losses than the MEA with Pt/C, although ohmic loss was the same as Pt/C. Finally, from the evaluation of cyclic voltammetry(CV), the unit cell using PtCo/MWNTs as the cathode electrocatalyst showed slightly higher fuel cell performance than the cell with a commercial Pt/C electrocatalyst.

• Journal of the Korean institute of surface engineering
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• v.49 no.6
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• pp.539-548
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• 2016

The non-noble 1D nanofibers(NFs) prepared by electrospinning and calcination method were used as oxygen evolution reaction (OER) electrocatalyst for water electrolysis. The electrospinning process and rate of solution composition was optimized to prepare uniform and non-beaded PVP polymer electrospun NFs. The diameter and morphology of PVP NFs changed in accordance with the viscosity and ion conductivity. The clean metal precursor contained electrospun fibers were synthesized via the optimized electrospinning process and solution composition. The calcined $CuCo_2O_4$ NFs catalyst showed higher activity and long-term cycle stability for OER compared with other $Co_3O_4$, $NiCo_2O$ NF catalysts. Furthermore, the $CuCo_2O_4$ NFs maintained the OER activity during long-term cycle test compared with commercial $CuCo_2O_4$ nanoparticle catalyst due to unique physicochemical and electrochemical properties by1D nanostructure.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.6
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• pp.256-259
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• 2006

The amorphous $SiO_x$ nanowires were synthesized by the vapor phase epitaxy (VPE) method. $SiO_x$ nanowires were formed on silicon wafer of temperatures ranged from $800{\sim}1100^{\circ}C$ and nickel thin film was used as a catalyst for the growth of nanowires. A vapor-liquid-solid (VLS) mechanism is responsible for the catalyst-assisted amorphous $SiO_x$ nanowires synthesis in this experiment. The SEM images showed cotton-like nanostructure of free standing $SiO_x$ nanowires with the length of more than about $10{\mu}m$. The $SiO_x$ nanowires were confirmed amorphous structure by TEM analysis and EDX spectrum reveals that the nanowires consist of Si and O.