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성에 제거용 대면적 투명 히터를 위한 환원된 산화 그래핀 연구
조승근,문해인,김영원,도환수,이정우 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.8
Transparent heaters are promising devices because of their versatile applications in vehicles, smart windows, and sensors, etc. Indium tin oxide is widely used for transparent heater materials due to its high electronic conductivity and visible light transmittance. However, the cost of indium is too high, and its fabrication needs sophisticated processes, so that many studies have focused on alternative materials which are inexpensive and easy-to-synthesize. Graphene is a two-dimensional material in which carbon atoms bond to form a hexagonal structure, and it can be an alternative material due to its superior electronic/ thermal conductivity and cost-effectiveness. Here, we chemically treated graphite to synthesize large-sized graphene oxide (LGO), and coated it on a glass substrate, followed by reduction using hydrogen iodide for large-sized reduced graphene oxide (LrGO) on glass. From surface characterizations, we confirmed that the lateral size of the LGO was over 50 μm and the LGO sheets were uniformly coated on the glass, which minimized intersheet contact resistance. Structural characterizations demonstrated that the LGO sheets were reduced to LrGO and the LrGO sheets coated on the glass showed a transmittance of 76.2 % at 550 nm with a sheet resistance of 0.98 kΩ. Finally, the temperature of the substrate increased up to 30 oC when 30 V of voltage was applied for 5 min, and the frost on the glass surface vanished within 1 min.
김상준,조승근,박길령,이은빈,이재민,이정우 한국재료학회 2022 한국재료학회지 Vol.32 No.2
Metal-organic frameworks (MOFs) are widely used in various fields because they make it easy to control porous structures according to combinations of metal ions and organic linkers. In addition, ZIF (zeolitic imidazolate framework), a type of MOF, is made up of transition metal ions such as Co2+ or Zn2+ and linkers such as imidazole or imidazole derivatives. ZIF- 67, composed of Co2+ and 2-methyl imidazole, exhibits both chemical stability and catalytic activity. Recently, due to increasing need for energy technology and carbon-neutral policies, catalysis applications have attracted tremendous research attention. Moreover, demand is increasing for material development in the electrocatalytic water splitting and metal-air battery fields; there is also a need for bifunctional catalysts capable of both oxidation/reduction reactions. This review summarizes recent progress of bifunctional catalysts for electrocatalytic water splitting and metal-air batteries using ZIF-67. In particular, the field is classified into areas of thermal decomposition, introduction of heterogeneous elements, and complex formation with carbonbased materials or polyacrylonitrile. This review also focuses on synthetic methods and performance evaluation.
루테늄 기반 전이금속 나노입자/환원된 산화그래핀 혼성체를 이용한 알칼리 수전해 촉매 합성
이은빈,조승근,김상준,박길령,이정우 대한금속·재료학회 2023 대한금속·재료학회지 Vol.61 No.3
Green hydrogen has attracted significant attention as one of the future energy sources because nogreenhouse gases are emitted during production and its energy density is much higher than fossil fuels. Precious metals such as platinum (Pt) and iridium (Ir)-based catalysts are commonly used for water splittingcatalysts. However, because of high cost of these precious metals, the mass production of green hydrogen isrestricted. In this study, water splitting catalysts based on relatively inexpensive ruthenium (Ru), cobalt (Co),and iron (Fe) were synthesized. The metal nanoparticles were anchored on reduced graphene oxide (rGO) bya microwave-assisted process. The nanoparticles were uniformly distributed on the rGO supports with sizesof about 1.5 and 2 nm in Ru/rGO and RuCoFe/rGO, respectively. This promoted the reaction by furtherincreasing the specific surface area of the catalysts. In addition, it was confirmed by EDS mapping resultsthat the nanoparticles were made of RuCoFe alloy. Among the prepared catalysts, Ru/rGO was excellenttoward the hydrogen evolution reaction (HER), which required an overpotential of 50 mV to reach a currentdensity of −10 mA cm−2. In addition, RuCoFe/rGO, which contained the RuCoFe alloy, was the best for theoxygen evolution reaction (OER), and it required 362 mV at the current density of 10 mA cm−2.
대면적 시트의 환원된 산화 그래핀을 활용한 메쉬 패턴 투명히터 제작
문해인,조승근,신유진,강여울,이정우 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.8
Transparent heaters are widely used for defrosting to improve visibility, insulation or heating of buildings, and thermal treatment. Indium tin oxide (ITO), which has excellent transmittance and electrical conductivity, is one of the representative materials used for these transparent heaters. However, it has several drawbacks including high material price, limited processability in large-area, and brittleness. Here, we fabricated a mesh-patterned transparent heater utilizing an inexpensive and solution-processable material, reduced graphene oxide, as an alternative to ITO. In this study, electrical conductivity was improved by the synthesis of large-sized reduced graphene oxide (LrGO). Over 80% of transmittance was obtained by adapting mesh patterns. Moreover, to alleviate the decrease in transmittance due to diffraction by the mesh pattern, transparent heaters were prepared with six different mesh patterns by changing the space between the repeating pattern units. Comparing the transmittance values from calculations and measurements, the HH (honeycomb-honeycomb) mesh pattern was determined to have the minimum degradation of transmittance due to diffraction. In addition, the electrical/optical properties and heating performances of LrGO meshpatterned transparent heaters were compared to confirm the optimal mesh pattern. As a result, frost was completely removed within 30 seconds under a low power of 0.07 W using a H-H 85% mesh patterned heater.
암모니아를 이용한 그래핀 구조 제어 및 고감도 압력 센서로의 적용
정연욱,조승근,문해인,김영원,신유진,박길령,이정우 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.3
Graphene has been used in various fields because of its excellent mechanical, optical, electrical, and thermal properties. However, its intrinsic low sensitivity to pressure limits its sensor applications. To overcome this drawback, many researchers have tried to improve the sensitivity by controlling the defects on the graphene, but have yet to report a significant increase in sensitivity compared to the pristine graphene. Herein, we fabricated a graphene-based highly sensitive pressure sensor by flowing ammonia gas during chemical vapor deposition. The ammonia gas assisted the generation of nano-sized defects due to nitrogen doping in the graphene lattice, as well as macro-sized cracks in the graphene layer, due to the corrosion of the Cu surface. We regulated the concentration ratio of ammonia gas and methane gas during the graphene synthesis, which controlled the crack generation. These cracks weakened the in-plane force of the networks in the geometric structure of the graphene, thereby allowing them to deform more easily under external force, and changing the resistance of the sensor dramatically. As a result, the sensitivity of the pressure sensor increased about 10,000 times higher than that of the pristine graphene. These results suggest that controlling defects to improve graphene’s mechanical sensitivity provides a promising route to pressure sensor applications.