• 한국세라믹학회지
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• 제51권4호
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• pp.265-270
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• 2014

Among the Ruddlesden-Popper series, $La_4Ni_3O_{10}$ has received widespread attention as a promising cathode material by reason of its favorable properties for realizing high performance of intermediate temperature solid oxide fuel cells (IT-SOFCs). The $La_4Ni_3O_{10}$ cathode is prepared using the facile sol-gel method by employing tri-blockcopolymer (F127) to obtain a single phase in a short sintering time. There are no reactions between the $La_4Ni_3O_{10}$ cathode and the $Ce_{0.9}Gd_{0.1}O_{2-\delta}$ (GDC) electrolyte upon sintering at $1000^{\circ}C$, indicating that the $La_4Ni_3O_{10}$ cathode has good chemical compatibility with the GDC electrolyte. The maximum electrical conductivity of $La_4Ni_3O_{10}$ reaches approximately 240 S $cm^{-1}$ at $100^{\circ}C$ and gradually decreases with increasing temperaturein air atmosphere. The area specific resistance value of $La_4Ni_3O_{10}$ composite with 40 wt% GDC is $0.435{\Omega}cm^2$ at $700^{\circ}C$. These data allow us to propose that the $La_4Ni_3O_{10}$-GDC composite cathode is a good candidate for IT-SOFC applications.

• 대한화학회지
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• 제21권6호
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• pp.404-412
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• 1977

에탄올-물 혼합용매에서 납전극을 사용하여 니트로벤젠(${\phi}NO_2$)과 그 유도체의 전해 환원반응을 조사하였다. 산성용액에서는 퍼텐셜에 따라 ${\phi}NHOH\;및\;{\phi}NH_2$가 생성되었으며 니트로벤젠(${\phi}NO$)은 중간체가 아닌것으로 보였다. 염기성 용액에서는 ${\phi}NO$가 생성되며 더 낮은 퍼텐셜에서 환원시키면 ${\phi}N=N{\phi}$ 등 짝지어진 화합물이 생성됨을 확인하였다. 사용한 전해질 용액에서 ${\phi}NO\;와\;{\phi}NHOH$ 사이에 화학적인 짝지음 반응(coupling reaction)은 일어나지 않았다. 각각의 반응에 대해 전류-전압관계와 pH 의존도 및 반응물질에대한 반응 차수로부터 반응 메카니즘을 도출하였다. ${\phi}NO$가 생성되는 반응은 치환기가 있을 때도 같은 메카니즘을 따르는 것으로 보인다.

• 한국세라믹학회지
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• 제48권5호
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• pp.479-484
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• 2011

In this paper, investigations of thick film $La_{0.75}Sr_{0.25}Ga_{0.8}Mg_{0.16}Fe_{0.04}O_{3-{\delta}}$ (LSGMF) cells fabricated via spin coating on either NiO-YSZ anode or $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_3$ (LSGF) cathode substrates are presented. A La-doped $CeO_2$ (LDC) layer is inserted between NiO-YSZ and LSGMF in order to prevent reactions from occurring during co-firing. For the LSGF cathode-supported cell, no interlayer was required because the components of the cathode are the same as those of LSGMF with the exception of Mg. An LSGMF electrolyte slurry was deposited homogeneously on the porous supports via spin coating. The current-voltage characteristics of the anode and cathode supported LSGMF cells at temperatures between $700^{\circ}C$ and $850^{\circ}C$ are described. The LSGF cathode supported cell demonstrates a theoretical OCV and a power density of ~420 mW $cm^2$ at $800^{\circ}C$, whereas the NiO-YSZ anode supported cell with the LDC interlayer demonstrates a maximum power density of ~350 mW $cm^2$ at $800^{\circ}C$, which decreased more rapidly than the cathode supported cell despite the presence of the LDC interlayer. Potential causes of the degradation at temperatures over $700^{\circ}C$ are also discussed.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.75.2-75.2
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• 2013

Atomic layer deposition (ALD), utilizing self-limiting surface reactions, could offer promising perspectives for future efficient energy conversion devices. The capabilities of ALD for surface/interface modification and construction of novel architectures with sub-nanometer precision and exceptional conformality over high aspect ratio make it more valuable than any other deposition methods in nanoscale science and technology. In the context, a variety of researches on fabrication of active materials for energy conversion applications by ALD are emerging. Among those materials, one-dimensional nanotubular titanium dioxide, providing not only high specific surface area but also efficient carrier transport pathway, is a class of the most intensively explored materials for energy conversion systems, such as photovoltaic cells and photo/electrochemical devices. The monodisperse, stoichiometric, anatase, TiO2 nanotubes with smooth surface morphology and controlled wall thickness were fabricated via low-temperature template-directed ALD followed by subsequent annealing. The ALD-grown, anatase, TiO2 nanotubes in alumina template show unusual crystal growth behavior which allows to form remarkably large grains along axial direction over certain wall thickness. We also fabricated dye-sensitized solar cells (DSCs) introducing our anatase TiO2 nanotubes as photoanodes, and studied the effect of blocking layer, TiO2 thin films formed by ALD, on overall device efficiency. The photon convertsion efficiency ~7% were measured for our TiO2 nanotubebased DSCs with blocking layers, which is ~1% higher than ones without blocking layer. We also performed open circuit voltage decay measurement to estimate recombination rate in our cells, which is 3 times longer than conventional nanoparticulate photoanodes. The high efficiency of our ALD-grown, anatase, TiO2 nanotube-based DSCs may be attributed to both enhanced charge transport property of our TiO2 nanotubes photoanode and the suppression of recombination at the interface between transparent conducting electrode and iodine electrolytes by blocking layer.

• 한국재료학회지
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• 제24권5호
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• pp.243-248
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• 2014

Silicon-carbon composite was prepared by the magnesiothermic reduction of mesoporous silica and subsequent impregnation with a carbon precursor. This was applied for use as an anode material for high-performance lithium-ion batteries. Well-ordered mesoporous silica(SBA-15) was employed as a starting material for the mesoporous silicon, and sucrose was used as a carbon source. It was found that complete removal of by-products ($Mg_2Si$ and $Mg_2SiO_4$) formed by side reactions of silica and magnesium during the magnesiothermic reduction, was a crucial factor for successful formation of mesoporous silicon. Successful formation of the silicon-carbon composite was well confirmed by appropriate characterization tools (e.g., $N_2$ adsorption-desorption, small-angle X-ray scattering, X-ray diffraction, and thermogravimetric analyses). A lithium-ion battery was fabricated using the prepared silicon-carbon composite as the anode, and lithium foil as the counter-electrode. Electrochemical analysis revealed that the silicon-carbon composite showed better cycling stability than graphite, when used as the anode in the lithium-ion battery. This improvement could be due to the fact that carbon efficiently suppressed the change in volume of the silicon material caused by the charge-discharge cycle. This indicates that silicon-carbon composite, prepared via the magnesiothermic reduction and impregnation methods, could be an efficient anode material for lithium ion batteries.

• 한국재료학회지
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• 제28권11호
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• pp.646-652
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• 2018

During a long-term operation of polymer electrolyte membrane fuel cells(PEMFCs), the fuel cell performance may degrade due to severe agglomeration and dissolution of metal nanoparticles in the cathode. To enhance the electrochemical durability of metal catalysts and to prevent the particle agglomeration in PEMFC operation, this paper proposes a hybrid catalyst structure composed of PtCo alloy nanoparticles encapsulated by porous carbon layers. In the hybrid catalyst structure, the dissolution and migration of PtCo nanoparticles can be effectively prevented by protective carbon shells. In addition, $O_2$ can properly penetrate the porous carbon layers and react on the active Pt surface, which ensures high catalytic activity for the oxygen reduction reaction. Although the hybrid catalyst has a much smaller active surface area due to the carbon encapsulation compared to a commercial Pt catalyst without a carbon layer, it has a much higher specific activity and significantly improved durability than the Pt catalyst. Therefore, it is expected that the designed hybrid catalyst concept will provide an interesting strategy for development of high-performance fuel cell catalysts.

• 한국분말재료학회지
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• 제28권2호
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• pp.127-133
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• 2021

One-dimensional (1D) piezoelectric nanostructures are attractive candidates for energy generation because of their excellent piezoelectric properties attributed to their high aspect ratios and large surface areas. Vertically grown BaTiO₃ nanotube (NT) arrays on conducting substrates are intensively studied because they can be easily synthesized with excellent uniformity and anisotropic orientation. In this study, we demonstrate the synthesis of 1D BaTiO₃ NT arrays on a conductive Ti substrate by electrochemical anodization and sequential hydrothermal reactions. Subsequently, we explore the effect of hydrothermal reaction conditions on the piezoelectric energy conversion efficiency of the BaTiO₃ NT arrays. Vertically aligned TiO₂ NT arrays, which act as the initial template, are converted into BaTiO₃ NT arrays using hydrothermal reaction with various concentrations of the Ba source and reaction times. To validate the electrical output performance of the BaTiO₃ NT arrays, we measure the electricity generated from each NT array packaged with a conductive metal foil and epoxy under mechanical pushings. The generated output voltage signals from the BaTiO₃ NT arrays increase with increasing concentration of the Ba source and reaction time. These results provide a new strategy for fabricating advanced 1D piezoelectric nanostructures by demonstrating the correlation between hydrothermal reaction conditions and piezoelectric output performance.

• 한국표면공학회지
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• 제56권4호
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• pp.243-249
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• 2023

Urea oxidation reaction (UOR) via electrochemical oxidation process can replace oxygen evolution reaction (OER) for green hydrogen production since UOR has lower thermodynamic potential (0.37 V_RHE) than that of OER (1.23 V_RHE). However, in the case of UOR, 6 electrons are required for the entire UOR. For this reason, the reaction rate is slower than OER, which requires 4 electrons. In addition, it is an important challenge to develop catalysts in which both oxidation reactions (UOR and OER) are active since the active sites of OER and UOR are opposite to each other. We prove that among the NiFe₂O₄ nanoparticles synthesized by the hydrothermal method at various synthesis temperatures, NiFe₂O₄ nanoparticle with properly controlled particle size and crystallinity can actively operate OER and UOR at the same time.

• 공업화학
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• 제34권6호
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• pp.567-575
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• 2023

물의 전기 분해는 효과적인 그린 수소를 생산하기 위한 유망한 기술 중 하나로서 활발한 연구가 이루어지고 있다. 수전해 시스템의 원료로 해수를 직접 사용하게 되면 지구상에 있는 물의 약 97%를 해수가 차지하고 있으므로, 기존 담수 원료의 제한성에 대한 문제를 해결할 수 있다. 동시에 풍부한 부생 원료를 얻을 수 있는데, 그 성분과 pH 환경에 따라 전기 분해 과정에서 생성되는 Cl₂, ClO^-, Br₂ 및 Mg(OH)₂ 등이 대표적이다. 성공적인 해수 수전해 시스템 개발과 이에 필수적인 산소발생반응(oxygen evolution reaction, OER)과 수소발생반응(hydrogen evolution reaction, HER) 촉매를 개발하기 위해서는 해수 환경에서 일어나는 반응의 원인과 결과에 대해 파악할 필요가 있다. 따라서 본 논문에서는 해수 수전해 시스템의 반응 메커니즘과 특징 및 애노드와 캐소드 전극에 사용되는 전기화학 촉매들의 연구 개발 동향에 대해 살펴보고자 한다.

• Korean Chemical Engineering Research
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• 제61권4호
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• pp.604-610
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• 2023

주변 조건에서 N₂를 환원하여 NH₃를 생성하는 전기 촉매 질소 환원 반응(nitrogen reduction reaction, NRR)은 산업공정에서 에너지 소비를 감소시킬 수 있는 유망한 기술로 주목을 받고 있다. N₂를 흡착하고 활성화할 수 있는 촉매 금속 표면 중 많이 사용되는 Ni(100) 표면의 여러 사이트(site)의 흡착 성능을 밀도 함수 이론 계산(density-functional theory)를 기반으로 비교하였다. 또한 안정적인 NRR반응의 경로를 유도하는 N₂의 두 가지 흡착 구조를 조사하였고 end-on 구조는 top site에 흡착, distal pathway로 반응이 진행되고 side-on 구조는 bridge site에 흡착되며 enzymatic pathway로 반응이 진행되었다. 마지막으로 구조 별 가장 안정한 메커니즘의 깁스 자유에너지를 구하여 반응의 경향성을 알아봄으로써 NRR 반응의 금속 촉매 표면 흡착에 대한 연구에 도움이 될 수 있을 것이다.