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용융 탄산염 연료전지용 gamma LiAlO₂ 전해질 지지체의 미세구조 및 기계적 강도 변화에 대한 B₂O₃ 첨가의 영향
함형철(Ham, Hyung-Chul),윤성필(Yoon, Sung-Pil),홍성안(Hong, Seong-Ah) 한국신재생에너지학회 2007 신재생에너지 Vol.3 No.1
A sintering aid, B₂O₃ have been included into a LiAlO₂ electrolyte support by a tape casting method in order to reinforce mechanical strength of the support for molten carbonate fuel cells [MCFCs). Starting idea originates from the low melting point of B₂O₃ (450?C), which can provide the low temperature consolidation of ceramic materials. The mechanical properties and the microstructure changes of the B₂O₃-included electrolyte support were examined by scanning electron microscope, mercury porosimetry, X-ray powder diffraction [XRD], high temperature differential scanning calorimeter and three-point bending strength measurement. The mechanical strength was clearly improved by addition of B₂O₃. The increase of mechanical strength results from the neck growth of a new LiAlO₂ phase between LiAlO₂ particles by the liquid phase sintering. Average pore size and porosity of the electrolyte support reinforced by addition of the sintering aid, B₂O₃, was 0.24{mu}m and 59%, respectively which were suitable microstructure of a matrix for an application of MCFCs.
함형철 ( Hyung Chul Ham ),윤성필 ( Sung Pil Yoon ),홍성안 ( Seong-ah Hong ) 한국신재생에너지학회 2007 신재생에너지 Vol.3 No.1
A sintering aid, B<sub>2</sub>O<sub>3</sub> have been included into a LiAlO<sub>2</sub> electrolyte support by a tape casting method in order to reinforce mechanical strength of the support for molten carbonate fuel cells [MCFCs). Starting idea originates from the low melting point of B<sub>2</sub>O<sub>3</sub> (450℃), which can provide the low temperature consolidation of ceramic materials. The mechanical properties and the microstructure changes of the B<sub>2</sub>O<sub>3</sub>-included electrolyte support were examined by scanning electron microscope, mercury porosimetry, X-ray powder diffraction [XRD], high temperature differential scanning calorimeter and three-point bending strength measurement. The mechanical strength was clearly improved by addition of B<sub>2</sub>O<sub>3</sub>. The increase of mechanical strength results from the neck growth of a new LiAlO<sub>2</sub> phase between LiAlO<sub>2</sub> particles by the liquid phase sintering. Average pore size and porosity of the electrolyte support reinforced by addition of the sintering aid, B<sub>2</sub>O<sub>3</sub>, was 0.24㎛ and 59%, respectively which were suitable microstructure of a matrix for an application of MCFCs.
개미산 분해 반응에서 수소 생산성 증대를 위한 Pd/Pd<sub>3</sub>Fe 합금 촉매: 범밀도 함수 이론 연구
조진원 ( Jinwon Cho ),한종희 ( Jonghee Han ),윤성필 ( Sung Pil Yoon ),남석우 ( Suk Woo Nam ),함형철 ( Hyung Chul Ham ) 한국화학공학회 2017 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.55 No.2
본 연구에서는 양자 역학 계산 이론 중 하나인 Density Functional Theory (DFT)를 사용하여 Pd/Pd<sub>3</sub>Fe 촉매 표면에서 개미산(HCOOH) 분해 반응으로부터 수소를 생산하는 반응 메커니즘을 분석하였다. 기존 연구에 따르면, 단일 원자 촉매 중에서 개미산 분해 반응에 가장 높은 수소 생산성을 기록하는 원자는 Pd 촉매이지만, 부 반응으로 생산되는 CO가 Pd에 독성을 띄우기 때문에 Pd 촉매의 성능을 저하시킨다. 이러한 단점을 극복하고자, Pd를 기반으로 Pd와 Fe를 3:1로 합금하여 Pd<sub>3</sub>Fe가 코어(core) 형태로 존재하고 Pd가 표면에 위치한 core-shell Pd/Pd<sub>3</sub>Fe 촉매를 설계하여 개미산 분해 반응에 의한 수소 생산 속도를 계산하였다. 순수 Pd촉매 보다 Pd/Pd<sub>3</sub>Fe 촉매의 수소 생산 반응의 활성 에너지가 감소 하였다. 그 이유는 Pd와 Fe가 합금화 되면서 Pd<sub>3</sub>Fe의 격자 상수가 2.76 A로 줄어 들어 HCOO의 흡착에너지를 0.03 eV 감소시켰고, Fe에서 표면 Pd로 전자가 이동하면서 표면 전자 구조가 변화하여 HCOO의 흡착에너지를 0.29 eV 낮추었기 때문이다. 본 연구에서 제안하는 결과를 바탕으로 추후 개미산으로부터 수소 생산이 더 용이한 새로운 촉매 설계 메커니즘을 제안하고자 한다. Formic acid has been known as one of key sources of hydrogen. Among various monometallic catalysts, hydrogen can be efficiently produced on Pd catalyst. However, the catalytic activity of Pd is gradually reduced by the blocking of active sites by CO, which is formed from the unwanted indirect oxidation of formic acid. One of promising solutions to overcome such issue is the design of alloy catalyst by adding other metal into Pd since alloying effect (such as ligand and strain effect) can increase the chance to mitigate CO poisoning issue. In this study, we have investigated formic acid deposition on the bimetallic Pd/Pd<sub>3</sub>Fe core-shell nanocatalyst using DFT (density functional theory) calculation. In comparison to Pd catalyst, the activation energy of formic acid dehydrogenation is greatly reduced on Pd/Pd<sub>3</sub>Fe catalyst. In order to understand the importance of alloying effects in catalysis, we decoupled the strain effect from ligand effect. We found that both strain effect and ligand effect reduced the binding energy of HCOO by 0.03 eV and 0.29 eV, respectively, compared to the pure Pd case. Our DFT analysis of electronic structure suggested that such decrease of HCOO binding energy is related to the dramatic reduction of density of state near the fermi level.