Metal-Nanowire-Electrode-Based Perovskite Solar Cells: Challenging Issues and New Opportunities

Ahn, Jihoon,Hwang, Hyewon,Jeong, Sunho,Moon, Jooho Wiley 2017 ADVANCED ENERGY MATERIALS Vol.7 No.15

Variation in Crystalline Phases: Controlling the Selectivity between Silicon and Silicon Carbide via Magnesiothermic Reduction using Silica/Carbon Composites

Ahn, Jihoon,Kim, Hee Soo,Pyo, Jung,Lee, Jin-Kyu,Yoo, Won Cheol American Chemical Society 2016 Chemistry of materials Vol.28 No.5

<P>Magnesiothermic reduction of various types of silica/carbon (SiO2/C) composites has been frequently used to synthesize silicon/carbon (Si/C) composites and silicon carbide (SiC) materials, which are of great interest in the research areas of lithium-ion batteries (LIBs) and nonmetal oxide ceramics, respectively. Up to now, however, it has not been comprehensively understood how totally different crystal phases of Si or SiC can result from the compositionally identical parent materials (SiO2/C) via magnesiothermic reduction. In this article, we propose a formation mechanism of Si and SiC by magnesiothermic reduction of SiO2/C; SiC is formed at the interface between SiO2 and carbon when silicon intermediates, mainly in situ-formed Mg2Si, encounter carbon through diffusion. Otherwise, Si is formed, which is supported by an ex situ reaction between Mg2Si and carbon nanosphere that results in SiC. In addition, the resultant crystalline phase ratio between Si and SiC can be controlled by manipulating the synthesis parameters such as the contact areas between silica and carbon of parent materials, reaction temperatures, heating rates, and amount of the reactant mixtures used. The reasons for the dependence on these synthesis parameters could be attributed to the modulated chance of an encounter between silicon intermediates and carbon, which determines the destination of silicon intermediates, namely, either thermodynamically preferred SiC or kinetic product of Si as a final product. Such a finding was applied to design and synthesize the hollow mesoporous shell (ca. 3-4 nm pore) SiC, which is particularly of interest as a catalyst support under harsh environments.</P>

Fabrication of Slippery Sticker with 3D Structures

Jihoon Ahn,Jaehyeon Jeon,Chang Sung Heu,Dong Rip Kim 한국생산제조학회 2018 한국생산제조시스템학회 학술발표대회 논문집 Vol.2018 No.10

Elucidating Relationships between Structural Properties of Nanoporous Carbonaceous Shells and Electrochemical Performances of Si@Carbon Anodes for Lithium-Ion Batteries

Ahn, Jihoon,Lee, Kyung Jae,Bak, Woojeong,Kim, Jung-Joon,Lee, Jin-Kyu,Yoo, Won Cheol,Sung, Yung-Eun American Chemical Society 2015 The Journal of Physical Chemistry Part C Vol.119 No.19

<P>The encapsulation of silicon in hollow carbonaceous shells (Si@C) is known to be a successful solution for silicon anodes in Li-ion batteries, resulting in many efforts to manipulate the structural properties of carbonaceous materials to improve their electrochemical performance. In this regard, we demonstrate in this work how both the shell thickness and pore size of nanoporous carbonaceous materials containing silicon anodes influence the electrochemical performance. Structurally well-defined Si@C materials with varying carbon-shell thicknesses and pore sizes were synthesized by a nanocasting method that manipulated the carbon shell and by a subsequent magnesiothermic reduction that converted the amorphous silica cores into silicon nanocrystals. When these materials were employed as anodes, it was verified that two opposite effects occur with respect to the thickness of carbon shell: The weight ratio of silicon and the electrical conductivity are simultaneously affected, so that the best electrochemical performance is not obtained from either the thickest or the thinnest carbon shell. Such countervailing effects were carefully confirmed through a series of electrochemical performance tests and the use of electrochemical impedance spectroscopy. In addition, the effect of pore size was elucidated by comparing Si@C samples with different pore sizes, revealing that larger pores can further improve the electrochemical performance as a result of enhanced Li-ion diffusion.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2015/jpccck.2015.119.issue-19/acs.jpcc.5b02073/production/images/medium/jp-2015-02073q_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp5b02073'>ACS Electronic Supporting Info</A></P>

Arsonic Acid As a Robust Anchor Group for the Surface Modification of Fe₃O₄

Ahn, Jihoon,Moon, Doo-Sik,Lee, Jin-Kyu American Chemical Society 2013 Langmuir Vol.29 No.48

<P>In order to use iron oxide nanoparticles (Fe<SUB>3</SUB>O<SUB>4</SUB>) in various applications, a surface modification that provides colloidal stability and additional functionality to the nanoparticles is necessary. For the modification of the nanoparticle surface with ligand molecules, the ligand molecule should contain an anchor group that has a strong affinity for the surface. However, currently used anchor groups have shown some problems such as low affinity and stability as well as reactivity with the surface. In this study, arsonic acid (RAsO(OH)<SUB>2</SUB>) was investigated as a novel anchor group. It was possible to introduce azide groups on the surface of iron oxide nanoparticles using 4-azidophenylarsonic acid, and the desired functional molecules could be chemically attached to the surface via copper-catalyzed azide–alkyne cycloaddition (click chemistry). By quantifying and comparing the amount of attached anchors on the surface, it was found that arsonic acid displays better affinity than other currently used anchors (catechol, carboxylic acid). Furthermore, we examined the binding reversibility, long–term anchoring stability, and anchoring stability at various pH values. It was revealed that arsonic acid is a stable anchor in various conditions.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2013/langd5.2013.29.issue-48/la402939r/production/images/medium/la-2013-02939r_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la402939r'>ACS Electronic Supporting Info</A></P>

Detection of Organic Vapors Based on Photoluminescent Bragg-Reflective Porous Silicon Interferomete.

Ahn, Jihoon,Cho, Bomin,Kim, Sungsoo,Sohn, Honglae American Scientific Publishers 2015 Journal of Nanoscience and Nanotechnology Vol.15 No.7

<P>Novel photoluminescent Bragg-reflective porous silicon, exhibiting dual optical properties, both the optical reflectivity and photoluminescence, was developed and used for sensing organic vapors. Photoluminescent Bragg-reflective porous silicon samples were prepared by an electrochemical etch of n-type silicon under the illumination. The etching solution consisted of a 3:1 volume mixture of aqueous 48% hydrofluoric acid and absolute ethanol. The typical etch parameters for the generation of photoluminescent Bragg-reflective porous silicon involved a periodic square wave current with 50 repeats. The surface of photoluminescent Bragg-reflective porous silicon was characterized by a FT-IR spectroscopy. Both reflectivity and photoluminescence were simultaneously measured under the exposure of organic vapors. The shift of reflection band to the longer wavelength and the quenching of photoluminescence under the exposure of various organic vapors were observed.</P>

Sea Sand-Derived Magnesium Silicide as a Reactive Precursor for Silicon-Based Composite Electrodes of Lithium-Ion Battery

Ahn, Jihoon,Lee, Dae-Hyeok,Kang, Min Seok,Lee, Kyung-Jae,Lee, Jin-Kyu,Sung, Yung-Eun,Yoo, Won Cheol Elsevier 2017 ELECTROCHIMICA ACTA Vol.245 No.-

<P><B>Abstract</B></P> <P>Recently, it has been clearly elucidated that nanostructured Si-based composites hybridized with protective and conductive materials can present enhanced electrochemical performance as anodes for Li-ion batteries (LIBs). One of remaining issues is to develop a sustainable and economic method to synthesize these composites on a large scale for industrial applications. Herein, we introduce a modified magnesiothermic reaction route to prepare the aforementioned Si-based composite electrodes using sea-sand derived Mg<SUB>2</SUB>Si as a reactive precursor. Owing to its reducibility and lability, Mg<SUB>2</SUB>Si can readily reduce group IVA oxides, such as Na<SUB>2</SUB>CO<SUB>3</SUB>, SiO<SUB>2</SUB>, GeO<SUB>2</SUB>, and SnO<SUB>2</SUB>, resulting in macroporous Si surrounded by the reduced forms of the counter reactants (C, Si, Ge, and Sn, respectively), some of which can be electrochemically attractive. Notably, the porous Si-based composite can be synthesized by a simple solid state reaction, so simplicity and scalability can be obtained. Also, the sea sand precursor is naturally–abundant; hence this process can be cost-effective, scalable, and sustainable. Porous Si@C composite can be synthesized from the modified magnesiothermic reaction using a sea sand-derived Mg<SUB>2</SUB>Si precursor, showing a specific capacity of 1000 mAh/g at 200th cycle. Potentially this process can be used for practical synthesis of Si-based composites.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We investigated Mg<SUB>2</SUB>Si as a reactive precursor for Si-based composite materials for Li-ion battery. </LI> <LI> Porous Si@C can be synthesized from naturally abundant sea sand using the reaction between sea sand-derived Mg<SUB>2</SUB>Si and Na<SUB>2</SUB>CO<SUB>3</SUB>. </LI> <LI> The reaction mechanism of the reaction between sea-sand derived Mg<SUB>2</SUB>Si and Na<SUB>2</SUB>CO<SUB>3</SUB> to form porous Si@C was investigated. </LI> <LI> Porous Si@C exhibits a large reversible capacity approximately 1000mAhg<SUP>−1</SUP> even after 200 cycles. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

R600a를 이용한 소형 멀티형 냉장고 시스템의 성능특성에 대한 실험적 연구

안지훈(Jihoon Ahn),장용희(Yonghee Jang),김용찬(Yongchan Kim),김용한(Yonghan Kim),장의영(Uiyoung Jang),박용종(Yongjong Park) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

Various types of refrigerators become popular in the market such as a common refrigerator, kimchi refrigerator and wine cellar. It is required to develop a multi function refrigerator which has different purposes in each evaporator. In this study, the performance of a multi type refrigerator system, which consists of one machine room and three evaporators, was measured in a bench type multi refrigerator. The multi type refrigerator system was tested by varying the number of refrigerator cabinet, refrigerant charge amount, compressor frequency and temperature condition. Based on experimental data, the multi type refrigerator showed better performance than the conventional refrigerator (single type). At the same external load condition, the COP of the multi type refrigerator was 1.2~1.5, but the COP of the single type refrigerator was 0.8. The single and multi type refrigerator cycles were optimized at -30.0℃ and -25.0℃, respectively. Therefore, the multi type refrigerator may show low compression ratio than the single type refrigerator.

인공지능교육 교과 융합을 위한 특수교육 교육과정 분석 및 교육 프로그램 개발

안지훈(JIHOON AHN),박형빈(HYOUNGBIN PARK) 한국인공지능윤리학회 2023 인공지능윤리연구 Vol.2 No.2

R600a를 이용한 소형 멀티형 냉장고 시스템의 성능특성에 대한 실험적 연구

안지훈(Jihoon Ahn),장용희(Yonghee Jang),김용찬(Yongchan Kim),최원섭(Wonseop Choi),오승환(Seungwhan Oh),김창년(Changnyeun Kim),이재승(Jaeseung Lee) 대한설비공학회 2009 설비공학 논문집 Vol.21 No.4

Various types of refrigerators become popular in the market such as a common refrigerator, kimchi refrigerator and wine cellar. It is required to develop a multi type refrigerator combining these refrigerators to save space and energy consumption. In this study. the performance of a multi type refrigerator, which consists of one machine room and three evaporators, was measured in a bench type multi refrigerator. The multi type refrigerator was tested by varying the number of refrigerator cabinet, refrigerant charge, and temperature conditions. In addition, the multi type refrigerator with a suction line heat exchanger(SLHX) was tested to improve system performance. Based on the experimental data, the multi type refrigerator showed better performance than the conventional refrigerator (single type system). Besides. the COP of the single system increased from 1.0 to 1.37, and those of the dual and triple system increased from 1.29 to 1.39, and 1.22 to 1.51, respectively, by applying the SLHX.