이중 전기방사법을 이용하여 SnO₂-Sn-Ag₃Sn 나노 입자가 균일하게 내재된 탄소 나노섬유의 합성

안건형,안효진,An, Geon-Hyoung,Ahn, Hyo-Jin 한국재료학회 2013 한국재료학회지 Vol.23 No.2

Well-distributed $SnO_2$-Sn-$Ag_3Sn$ nanoparticles embedded in carbon nanofibers were fabricated using a co-electrospinning method, which is set up with two coaxial capillaries. Their formation mechanisms were successfully demonstrated. The structural, morphological, and chemical compositional properties were investigated by field-emission scanning electron spectroscopy (FESEM), bright-field transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In particular, to obtain well-distributed $SnO_2$ and Sn and $Ag_3Sn$ nanoparticles in carbon nanofibers, the relative molar ratios of the Ag precursor to the Sn precursor including 7 wt% polyacrylonitrile (PAN) were controlled at 0.1, 0.2, and 0.3. The FESEM, bright-field TEM, XRD, and XPS results show that the nanoparticles consisting of $SnO_2$-Sn-$Ag_3Sn$ phases were in the range of ~4 nm-6 nm for sample A, ~5 nm-15 nm for sample B, ~9 nm-22 nm for sample C. In particular, for sample A, the nanoparticles were uniformly grown in the carbon nanofibers. Furthermore, when the amount of the Ag precursor and the Sn precursor was increased, the inorganic nanofibers consisting of the $SnO_2$-Sn-$Ag_3Sn$ nanoparticles were formed due to the decreased amount of the carbon nanofibers. Thus, well-distributed nanoparticles embedded in the carbon nanofibers were successfully synthesized at the optimum molar ratio (0.1) of the Ag precursor to the Sn precursor after calcination of $800^{\circ}C$.

루테늄 산화물 나노 섬유 지지체에 담지된 고 분산성 촉매의 전기화학적 거동

안건형,안효진,An, Geon-Hyoung,Ahn, Hyo-Jin 한국분말야금학회 2017 한국분말재료학회지 (KPMI) Vol.24 No.2

Well-dispersed platinum catalysts on ruthenium oxide nanofiber supports are fabricated using electrospinning, post-calcination, and reduction methods. To obtain the well-dispersed platinum catalysts, the surface of the nanofiber supports is modified using post-calcination. The structures, morphologies, crystal structures, chemical bonding energies, and electrochemical performance of the catalysts are investigated. The optimized catalysts show well-dispersed platinum nanoparticles (1-2 nm) on the nanofiber supports as well as a uniform network structure. In particular, the well-dispersed platinum catalysts on the ruthenium oxide nanofiber supports display excellent catalytic activity for oxygen reduction reactions with a half-wave potential ($E_{1/2}$) of 0.57 V and outstanding long-term stability after 2000 cycles, resulting in a lower $E_{1/2}$ potential degradation of 19 mV. The enhanced electrochemical performance for oxygen reduction reactions results from the well-dispersed platinum catalysts and unique nanofiber supports.

산소환원반응 촉매용 질소 도핑된 탄소나노섬유의 제조

안건형,이은환,안효진,An, Geon-Hyoung,Lee, Eun-Hwan,Ahn, Hyo-Jin 한국분말야금학회 2016 한국분말재료학회지 (KPMI) Vol.23 No.6

N-doped carbon nanofibers as catalysts for oxygen-reduction reactions are synthesized using electrospinning and carbonization. Their morphologies, structures, chemical bonding states, and electrochemical performance are characterized. The optimized N-doped carbon nanofibers exhibit graphitization of carbon nanofibers and an increased nitrogen doping as well as a uniform network structure. In particular, the optimized N-doped carbon nanofibers show outstanding catalytic activity for oxygen-reduction reactions, such as a half-wave potential ($E_{1/2}$) of 0.43 V, kinetic limiting current density of $6.2mAcm^{-2}$, electron reduction pathways (n = 3.1), and excellent long-term stability after 2000 cycles, resulting in a lower $E_{1/2}$ potential degradation of 13 mV. The improvement in the electrochemical performance results from the synergistic effect of the graphitization of carbon nanofibers and the increased amount of nitrogen doping.

$TiO_2$기반 복합 나노선을 이용한 리튬이온 배터리의 전극 특성 연구

안건형,안효진,An, Geon-Hyoung,Ahn, Hyo-Jin 한국마이크로전자및패키징학회 2011 마이크로전자 및 패키징학회지 Vol.18 No.3

우리는 전기방사법을 이용하여 $TiO_2$-Ag 복합 나노선 전극을 성공적으로 합성 하였으며 그들의 전기화학적 특성 및 구조 사이의 관계를 주사전자현미경(FESEM), 투과전자현미경(TEM), X-선 회절(XRD), X-선 광전자 분광법(XPS) 및 cycler에 의하여 규명하였다. 특히 $TiO_2$-Ag 복합 나노선 전극의 전기화학 특성은 순수한 $TiO_2$ 나노선 전극 및 나노입자(P25, Degussa)와 비교하였을 때 우수한 전기화학적 결과를 얻었다. 따라서 $TiO_2$ 나노선 전극 안에 Ag nanophases의 도입은 리튬이온 배터리를 위한 나노선 전극의 수명 및 용량을 향상 시킬 수 있다. we successfully synthesized $TiO_2$-Ag composite nanowires via an electrospinning method and investigated the relationship between their electrochemical properties and structures by means of field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and cycler. It is shown that the $TiO_2$-Ag composite nanowires exhibit superior electrochemical properties when compared to the single $TiO_2$ nanowires and $TiO_2$ nanoparticles (P25, Degussa). Therefore, the results indicate that the introduction of Ag nanophases within the electrospun $TiO_2$ nanowires could be improved the capacitance and cycleability of electrodes in Li-ion batteries.

다공성 탄소나노섬유 지지체에 담지된 백금촉매의 메탄올 산화 특성 연구

신동요,안건형,안효진,Sin, Dong-Yo,An, Geon-Hyoung,Ahn, Hyo-Jin 한국재료학회 2015 한국재료학회지 Vol.25 No.3

To improve the methanol electro-oxidation in direct methanol fuel cells(DMFCs), Pt electrocatalysts embedded on porous carbon nanofibers(CNFs) were synthesized by electrospinning followed by a reduction method. To fabricate the porous CNFs, we prepared three types of porous CNFs using three different amount of a styrene-co-acrylonitrile(SAN) polymer: 0.2 wt%, 0.5 wt%, and 1 wt%, respectively. A SAN polymer, which provides vacant spaces in porous CNFs, was decomposed and burn out during the carbonization. The structure and morphology of the samples were examined using field emission scanning electron microscopy and transmission electron microscopy and their surface area were measured using the Brunauer-Emmett-Teller(BET). The crystallinities and chemical compositions of the samples were examined using X-ray diffraction and X-ray photoelectron spectroscopy. The electrochemical properties on the methanol electro-oxidation were characterized using cyclic voltammetry and chronoamperometry. Pt electrocatalysts embedded on porous CNFs containing 0.5 wt% SAN polymer exhibited the improved methanol oxidation and electrocatalytic stability compared to Pt/conventional CNFs and commercial Pt/C(40 wt% Pt on Vulcan carbon, E-TEK).

Electrochemical capacitor를 위한 Ru 나노입자가 담지 된 다공성 탄소 나노섬유의 제조

이유진,안건형,안효진,Lee, Yu-Jin,An, Geon-Hyoung,Ahn, Hyo-Jin 한국재료학회 2014 한국재료학회지 Vol.24 No.1

Well-distributed ruthenium (Ru) nanoparticles decorated on porous carbon nanofibers (CNFs) were synthesized using an electrospinning method and a reduction method for use in high-performance elctrochemical capacitors. The formation mechanisms including structural, morphological, and chemical bonding properties are demonstrated by means of field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). To investigate the optimum amount of the Ru nanoparticles decorated on the porous CNFs, we controlled three different weight ratios (0 wt%, 20 wt%, and 40 wt%) of the Ru nanoparticles on the porous CNFs. For the case of 20 wt% Ru nanoparticles decorated on the porous CNFs, TEM results indicate that the Ru nanoparticles with ~2-4 nm size are uniformly distributed on the porous CNFs. In addition, 40 wt% Ru nanoparticles decorated on the porous CNFs exhibit agglomerated Ru nanoparticles, which causes low performance of electrodes in electrochemical capacitors. Thus, proper distribution of 20 wt% Ru nanoparticles decorated on the porous CNFs presents superior specific capacitance (~280.5 F/g at 10 mV/s) as compared to the 40 wt% Ru nanoparticles decorated on the porous CNFs and the only porous CNFs. This enhancement can be attributed to the synergistic effects of well-distributed Ru nanoparticles and porous CNF supports having high surface area.

수소제조를 위한 다공성 FeCrAl 금속 합금 Foam의 NiO 촉매 담지 및 미세구조 분석

이유진,안건형,박만호,이창우,최상현,정주용,조성종,이근재,안효진,Lee, Yu-Jin,An, Geon-Hyoung,Park, Man-Ho,Lee, Chang-Woo,Choi, Sang-Hyun,Jung, Ju-Yong,Jo, Sung-Jong,Lee, Kun-Jae,Ahn, Hyo-Jin 한국재료학회 2014 한국재료학회지 Vol.24 No.8

NiO catalysts were successfully coated onto FeCrAl metal alloy foam as a catalyst support via a dip-coating method. To demonstrate the optimum amount of NiO catalyst on the FeCrAl metal alloy foam, the molar concentration of the Ni precursor in a coating solution was controlled, with five different amounts of 0.4 M, 0.6 M, 0.8 M, 1.0 M, and 1.2 M for a dip-coating process. The structural, morphological, and chemical bonding properties of the NiO-catalyst-coated FeCrAl metal alloy foam samples were assessed by means of field-emission scanning electron microscopy(FESEM), scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS), X-ray diffraction(XRD), and X-ray photoelectron spectroscopy(XPS). In particular, when the FeCrAl metal alloy foam samples were coated using a coating solution with a 0.8 M Ni precursor, well-dispersed NiO catalysts on the FeCrAl metal alloy foam compared to the other samples were confirmed. Also, the XPS results exhibited the chemical bonding states of the NiO phases and the FeCrAl metal alloy foam. The results showed that a dip-coating method is one of best ways to coat well-dispersed NiO catalysts onto FeCrAl metal alloy foam.

산소환원반응을 위한 탄화철이 내재된 질소 도핑된 탄소의 제조

이영근,안건형,안효진,Lee, Young-Geun,An, Geon-Hyoung,Ahn, Hyo-Jin 한국재료학회 2018 한국재료학회지 Vol.28 No.11

The design of non-precious electrocatalysts with low-cost, good stability, and an improved oxygen reduction reaction(ORR) to replace the platinium-based electrocatalyst is significant for application of fuel cells and metal-air batteries with high energy density. In this study, we synthesize iron-carbide($Fe_3C$) embedded nitrogen(N) doped carbon nanofiber(CNF) as electrocatalysts for ORRs using electrospinning, precursor deposition, and carbonization. To optimize electrochemical performance, we study the three stages according to different amounts of iron precursor. Among them, $Fe_3C$-embedded N doped CNF-1 exhibits the most improved electrochemical performance with a high onset potential of -0.18 V, a high $E_{1/2}$ of -0.29 V, and a nearly four-electron pathway (n = 3.77). In addition, $Fe_3C$-embedded N doped CNF-1 displays exellent long-term stabillity with the lowest ${\Delta}E_{1/2}=8mV$ compared to the other electrocatalysts. The improved electrochemical properties are attributed to synergestic effect of N-doping and well-dispersed iron carbide embedded in CNF. Consequently, $Fe_3C$-embedded N doped CNF is a promising candidate for non-precious electrocatalysts for high-performance ORRs.

전기 이중층 커패시터용 메조 다공성 탄소 나노섬유의 제조

이도영,안건형,안효진,Lee, Do-Young,An, Geon-Hyoung,Ahn, Hyo-Jin 한국재료학회 2017 한국재료학회지 Vol.27 No.11

Mesoporous carbon nanofibers as electrode material for electrical double-layer capacitors(EDLCs) are fabricated using the electrospinning method and carbonization. Their morphologies, structures, chemical bonding states, porous structure, and electrochemical performance are investigated. The optimized mesoporous carbon nanofiber has a high sepecific surface area of $667m^2\;g^{-1}$, high average pore size of 6.3 nm, and high mesopore volume fraction of 80 %, as well as a unifom network structure consiting of a 1-D nanofiber stucture. The optimized mesoporous carbon nanofiber shows outstanding electrochemical performance with high specific capacitance of $87F\;g^{-1}$ at a current density of $0.1A\;g^{-1}$, high-rate performance ($72F\;g^{-1}$ at a current density of $20.0A\;g^{-1}$), and good cycling stability ($92F\;g^{-1}$ after 100 cycles). The improvement of the electrochemical performance via the combined effects of high specific surface area are due to the high mesopore volume fraction of the carbon nanofibers.

산화환원반응용 백금 촉매 지지체를 위한 질소 도핑된 단백질계 탄소의 제조

이영근,안건형,안효진,Lee, Young-geun,An, Geon-hyeong,Ahn, Hyo-Jin 한국재료학회 2018 한국재료학회지 Vol.28 No.3

Nitrogen (N)-doped protein-based carbon as platinum (Pt) catalyst supports from tofu for oxygen reduction reactions are synthesized using a carbonization and reduction method. We successfully prepare 5 wt% Pt@N-doped protein-based carbon, 10 wt% Pt@N-doped protein-based carbon, and 20 wt% Pt@N-doped protein-based carbon. The morphology and structure of the samples are characterized by field emission scanning electron microscopy and transmission electron micro scopy, and crystllinities and chemical bonding are identified using X-ray diffraction and X-ray photoelectron spectroscopy. The oxygen reduction reaction are measured using a linear sweep voltammogram and cyclic voltammetry. Among the samples, 10 wt% Pt@N-doped protein-based carbon exhibits exellent electrochemical performance with a high onset potential of 0.62 V, a high $E_{1/2}$ of 0.55 V, and a low ${\Delta}E_{1/2}=0.32mV$. Specifically, as compared to the commercial Pt/C, the 10 wt% Pt@N-doped protein-based carbon had a similar oxygen reduction reaction perfomance and improved electrochemical stability.