Fabrication of β-FeOOH@Hollow SiO2 particles and their coloration behavior via annealing temperature

Gye Seok An,Ri Yu,YooJin Kim 한양대학교 세라믹연구소 2017 Journal of Ceramic Processing Research Vol.18 No.10

In this study, we synthesized a hollow structured core-shell β-FeOOH@SiO2 particles via etching treatment with mild basic solution. The rod shaped β-FeOOH particles were prepared by hydrolysis of FeCl3 as a raw material and subsequently coated with silica via sol-gel method. The hollow shell layer was fabricated by dissolution of SiO2 shell from core-shell β- FeOOH@SiO2 particles in certain NH4OH solution. We have been found that the thermal stability of a hollow SiO2 coating layer having a relatively low density is sufficiently maintained to a temperature at a very specific high temperature equivalent to common core-shell structure. Particularly, the crystal phase and morphology of core shell particles, which have a large effect on the chromaticity, were transferred at about 500 o C. Moreover, the chromaticity of the core-shell particles was not significantly decreased due to individual phase transition in the state of being trapped in the coating layer.

Tunnel-type β-FeOOH cathode material for high rate sodium storage via a new conversion reaction

Cho, Min Kyoung,Jo, Jae Hyeon,Choi, Ji Ung,Kim, Jongsoon,Yashiro, Hitoshi,Yuan, Shuai,Shi, Liyi,Sun, Yang-Kook,Myung, Seung-Taek Elsevier 2017 Nano energy Vol.41 No.-

<P><B>Abstract</B></P> <P>We have investigated a tunnel-type β-FeOOH cathode material for rapid sodium storage. Rietveld refinement of the X-ray diffraction (XRD) data obtained for β-FeOOH indicated that the structure was stabilized into [2 × 2] hollandite tunnel structure, and the adhesion of the β-FeOOH onto carbon nanotubes (CNTs) led to a high electrical conductivity of 3Scm<SUP>−1</SUP>. As a result, the β-FeOOH/CNTs composite electrode showed excellent electrode performance, with a discharge capacity of 205 mAh g<SUP>−1</SUP> and a coulombic efficiency of 88.5% in the voltage range of 1.1–4V during the first cycle, 131 mAh g<SUP>−1</SUP> after 200 cycles, and a capacity retention of 70% over 300 cycles at 10C (1920mAg<SUP>−1</SUP>). Based on the XRD, X-ray absorption, and time-of-flight secondary-ion mass spectroscopy results, we suggest a new conversion mechanism for the β-FeOOH cathode material in Na cells, namely, FeOOH + Na<SUP>+</SUP> + e<SUP>-</SUP> → FeO + NaOH. This conversion reaction produces NaOH as a byproduct, and the reaction is fairly reversible even at 10 C-rates.</P> <P><B>Highlights</B></P> <P> <UL> <LI> β-FeOOH/CNTs composite is suggested as an cathode material for Na-ion batteries. </LI> <LI> β-FeOOH/CNTs composite is activated by a new conversion reaction via Fe<SUP>3+/2+</SUP> redox. </LI> <LI> β-FeOOH/CNTs composite shows a high electric conductivity, 3Scm<SUP>−1</SUP>. </LI> <LI> β-FeOOH/CNTs composite is fairly reversible at high rates for a long term. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>We report on tunnel type β-FeOOH nano-stick particles embedded in carbon nanotubes. The β-FeOOH/CNTs composite represents rapid sodium storage capability via a new conversion reaction, which is fairly reversible at high rates for a long term.</P> <P>[DISPLAY OMISSION]</P>

Micro-Flower NiCoMnO2 Superstructures Prepared by a Catalytic Chemical Oxidation for Supercapacitor Applications

조영훈,고태훈,최웅기,국윤수,서민강,김병석 한국섬유공학회 2020 한국섬유공학회지 Vol.57 No.5

Herein, a facile method of catalytic chemical oxidation was reported to produce the micro-flower NiCoMnO2 superstructures. FE-SEM confirmed the uniform NiCoMnO2 flower-like morphologies with an averaged diameter of 1−2 μm, composed of the nanosheets with the thickness of 10 ± 2 nm, could provide the pathways for efficient and fast transport of both electrolyte ions and electrons due to higher electroactive surface areas and enhanced electrical conductivity. As an anode material, nanorod-like β-FeOOH with the average diameter of 139 ± 30 nm and the length of 796 ± 140 nm was obtained by a hydrothermal method. The NiCoMnO2 and β-FeOOH electrode materials showed the good electrochemical performance with maximum specific capacitances of 726 F g-1 and 276 F g-1 at 1 A g-1, respectively. Furthermore, the fabricated asymmetric supercapacitor (ASC) NiCoMnO2//β-FeOOH device exhibited excellent specific capacitance of 110 F g-1 at 1 A g-1, cycle stability of 84.5% after 2000 charge/discharge cycles and high energy density of 34.38 Wh kg-1 at the power density of 750 W kg-1.

보존처리 후 철제유물에 생성된 부식물 특성 연구

정지해,양희제,하진욱 한국문화재보존과학회 2013 보존과학회지 Vol.29 No.4

철제유물은 출토되는 순간 급격한 환경변화로 인해 빠른 속도로 부식이 진행되므로 보존처리 과정을 거쳐 부식을 억제한다. 그러나 보존처리가 완료된 철제유물도 재부식이 발생하는 경우가 다수이며, 재부식된 유물의 보존처리는 1차 보존처리 시보다 그 처리가 어렵고 처리기간 또한 길어진다. 본 연구는 보존처리가 완료된 이후 보관과정에서 발생하는 부식생성물을 과학적으로 분석하여 재부식의 요인을 찾고자 하였다. 경주지역의 세 유적에서 출토된 철제유물을 동일한 약품과 방법으로 2002∼2009년 동안 보존처리를 완료하였으나, 포장·보관 상태의 일부 철제유물에서 재부식 징후가 관찰되었다. 이중 재부식의 징후가 확인된 단조 철제유물 9점을 선별하여 질량측정, 육안관찰, 현미경을 통한 물리적 변화를 관찰하였고, SEM-EDS, XRD, IC, ICP분석을 통해 화학적 변화를 분석하였다. 그 결과, 유물에서 탈락된 부분의 접면에 형성된 황갈색 부식생성물은 군집한 형상만 다를 뿐 결정상은 공통적으로 침상형이 확인되었으며, 적색에서 황갈색으로 갈수록 침상의 형태가 뚜렷하였다. 보존처리가 완료된 시점의 경과에 따라 부식생성물이 증가할수록 유물의 질량이 증가하였고 염화이온의 농도가 상대적으로 높아지는 경향이 나타났다. 채집된 모든 시료의 부식생성물에 대한 XRD분석에서는 β-FeOOH(akaganeite)이 확인되었고, ICP분석 결과 Na+, Ca2+ 성분을 확인할 수 있었다.

Cathodic shift in onset potential of hematite photoanodes by ZrO2 underlayer for efficient water splitting

( Subramanian Arunprabaharan ),( Alagappan Annamalai ),( Jum Suk Jang ) 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.0

Herein we report that influence of Zr underlayer to hematite photoanodes for cathodic shift in onset potential as well as photocurrent. Akaganite (β-FeOOH) nanorods were grown on Zr underlayer treated FTO substrates. Sintering at 800°C transforms the akaganite to hematite phase and induces the Sn atoms from the FTO substrates will penetrate in to the hematite lattices along with Zr atoms. Zr underlayer treated sample shows the better performance of water splitting compared to the pristine photoanode. Cathodic shift in onset potential as well as photocurrent was done by penetration of Zr atoms from the underlayer to hematite lattices. 0.96 mA/cm2 at 1.23 VRHE was achieved for Zr based hematite photoanode with low turn on voltage 0.7 V vs. RHE. The crystalline structure and morphology for the Zr modified hematite photoanode almost identical to the pristine photoanode. Presence of Zirconium and Sn diffusion from the FTO were confirmed by XPS analysis. Electrochemical Impedance Spectroscopy reveals that the presence of Zr underlayer increases the charge transfer resistance along the various interfaces. The presence of ZrO2 underlayer decreases the FTO deformation and the sheet resistance of FTO is decreased. Mott Schottky analysis reveals that the donor density and flat band potential of the pristine and Zr underlayer treated photoanodes shows similar values. This is the first report on Zr underlayer based hematite photoanodes for the increment in photocurrent and cathodic shift in onset potential.

Fabrication of superior α-Fe₂O₃ nanorod photoanodes through ex-situ Sn-doping for solar water splitting

Annamalai, Alagappan,Shinde, Pravin S.,Jeon, Tae Hwa,Lee, Hyun Hwi,Kim, Hyun Gyu,Choi, Wonyong,Jang, Jum Suk Elsevier 2016 Solar energy materials and solar cells Vol.144 No.-

<P><B>Abstract</B></P> <P>Doping transition metals into 1-D nanostructures is of crucial importance for their application in photovoltaics and photoelectrochemical (PEC) systems; performance enhancements arise from both dopant incorporation and the 1-D nanostructures. Both in-situ and ex-situ doping methods have been demonstrated for 1-D hematite (α-Fe<SUB>2</SUB>O<SUB>3</SUB>) nanostructures, with tin (Sn) as the dopant, for photoelectrochemical water oxidation. In-situ Sn-doped hematite photoanodes adopted a morphology consisting of nanocorals with the (104) plane as the preferred direction of crystal growth. As an alternative solution, ex-situ doping not only preserves the vertically-aligned nanorod morphology but also sustains the preferred orientation of the (110) axis, which is favorable for high conductivity in pristine hematite photoanodes. In-situ Sn-doping was carried out by the same method: Sn precursors were added and dissolved in ethanol during the hydrothermal synthesis. Ex-situ doping was carried out in two stages (during pre-deposition and during high temperature sintering). During pre-deposition, a defined amount of the Sn precursor was introduced near the surface region of the 1-D nanostructure, and the Sn content was controlled by changing the concentration of the precursor solution. In subsequent high temperature sintering (800°C), the dopant atoms diffused into the hematite lattice to attain the desired doping profile. We found that ex-situ Sn-doping resulted in a 60% increase in the photocurrent while in-situ Sn-doping yielded an increase of only 20% in the photocurrent, as compared with pristine hematite photoanodes, at 1.4 V <I>vs.</I> RHE. The improvement in the photocurrent was caused by a combination of Sn dopants in the hematite, which act as electron donors by increasing the donor density, and better surface charge transfer kinetics, thereby enhancing the overall device performance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> In-situ and ex-situ doping methods were compared for α-Fe<SUB>2</SUB>O<SUB>3</SUB> with Sn as a dopant. </LI> <LI> Ex-situ Sn-doping has 60% higher photocurrent compared to pristine photoanodes. </LI> <LI> Ex-Situ retains highly conductive (110) crystal plane and nanorod morphology. </LI> <LI> In-situ has lot of grain boundaries (nano-corals) and less conductive (104) phase. </LI> <LI> All doping problems related to β-FeOOH phase has been avoided in ex-situ doping. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

침염시킨 철기 유물 표면 위에 형성된 부식 생성물과 탈염처리에 대한 연구

민심근(Sim-Kun Min),이재형(Jae Hyung Lee),이재봉(Jae-Bong Lee),안병찬(Byeong-Chan An) 한국표면공학회 2007 한국표면공학회지 Vol.40 No.1

Excavated archaeological iron artifacts are usually conducted the conservation treatment for removal of chloride ions in the corrosion products. However, some iron artifacts are corroded again even after the conservation treatment due to unremoved chloride ions. Therefore, it is important to prevent desalinized artifacts from the occurrence of corrosion after the treatment. In this paper, we investigated the characteristics of corrosion products on salinized iron artifacts and evaluated the variety of desalination methods such as autoclave, intensive washing and NaOH. It was also found that β-FeOOH (Akaganeite) played an important role on the occurrence of corrosion and the treatment for removal of chloride ions. The extents of desalination were compared between the desalination methods. Results showed that the auto-clave method represented the highest efficiency for desalination while the intensive washing method was the lowest.