• Title/Summary/Keyword: 산화 환원 반응

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Fundamental Mechanisms of Platinum Catalyst for Oxygen Reduction Reaction in Fuel Cell: Density Functional Theory Approach (연료전지 산소환원반응 향상 위한 백금 촉매의 구조적 특성: 밀도범함수이론 연구)

  • Kang, Seok Ho;Lee, Chang-Mi;Lim, Dong-Hee
    • Journal of Korean Society of Environmental Engineers
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    • v.38 no.5
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    • pp.242-248
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    • 2016

  • The overall reaction rate of fuel cell is governed by oxygen reduction reaction (ORR) in the cathode due to its slowest reaction compared to the oxidation of hydrogen in the anode. The ORR efficiency can be readily evaluated by examining the adsorption strength of atomic oxygen on the surface of catalysts (i.e., known as a descriptor) and the adsorption energy can be controlled by transforming the surface geometry of catalysts. In the current study, the effect of the surface geometry of catalysts (i.e., strain effect) on the adsorption strength of atomic oxygen on platinum catalysts was analyzed by using density functional theory (DFT). The optimized lattice constant of Pt ($3.977{\AA}$) was increased and decreased by 1% to apply tensile and compressive strain to the Pt surface. Then the oxygen adsorption strengths on the modified Pt surfaces were compared and the electron charge density of the O-adsorbed Pt surfaces was analyzed. As the interatomic distance increased, the oxygen adsorption strength became stronger and the d-band center of the Pt surface atoms was shifted toward the Fermi level, implying that anti-bonding orbitals were shifted to the conduction band from the valence band (i.e., the anti-bonding between O and Pt was less likely formed). Consequently, enhanced ORR efficiency may be expected if the surface Pt-Pt distance can be reduced by approximately 2~4% compared to the pure Pt owing to the moderately controlled oxygen binding strength for improved ORR.

  • https://doi.org/10.4491/KSEE.2016.38.5.242 인용 PDF KSCI

Selection of the Best Oxygen Carrier Particle for Syngas Fueled Chemical-Looping Combustor (합성가스 연소 매체순환식 가스연소기 적용을 위한 최적 산소공여입자 선정)

  • Ryu, Ho-Jung;Kim, Ji-Woong;Jo, Wan-Kuen;Park, Moon-Hee
    • Korean Chemical Engineering Research
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    • v.45 no.5
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    • pp.506-514
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    • 2007

  • To select the best oxygen carrier particle for syngas fueled chemical-looping combustor, the reduction reactivity and carbon deposition characteristics were determined in a thermogravimetric analyzer. Four kinds of oxygen carrier particles (NiO/bentonite, $NiO/LaAl_{11}O_{18}$, $Co_xO_y/CoAl_2O_4$, $NiO/NiAl_2O_4$) were tested with the simulated syngas (30% $H_2$, 10% $CO_2$, 60% CO) as a reduction gas. With each of these particles, the maximum conversion and oxygen transfer capacity increase with increasing the reduction temperature At the given experimental range, the optimum operating temperature to maximize oxygen transfer rate is found to be $900^{\circ}C$ and carbon deposition on the particles could avoid at the temperature above $800^{\circ}C$. Among four kinds of oxygen carrier particles, the NiO-based particles exhibits better reactivity than the CoO-based particle. Moreover, the NiO/bentonite particle produces the best reactivity based on the oxygen transfer rate and the degree of carbon deposition. The measured oxygen transfer rate increases as the metal oxide content in NiO/bentonite particle is increased thereby higher metal oxide contents could provide stable operation of chemical-looping combustor.

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Low Temperature CO Oxidation over Cu-Mn Mixed Oxides (Cu-Mn 혼합산화물 상에서 일산화탄소의 저온산화반응)

  • Cho, Kyong-Ho;Park, Jung-Hyun;Shin, Chae-Ho
    • Clean Technology
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    • v.16 no.2
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    • pp.132-139
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    • 2010

  • The Cu-Mn mixed oxide catalysts with different molar ratios of Cu/(Cu+Mn) prepared by co-precipitation method have been investigated in CO oxidation at $30^{\circ}C$. The catalysts used in this study were characterized by X-ray Diffraction (XRD), $N_2$ sorption, X-ray photoelectron spectroscopy (XPS), and $H_2$-temperature programmed reduction $(H_2-TPR)$ to correlate with catalytic activities in CO oxidation. The $N_2$ adsorption-desorption isotherms of Cu-Mn mixed oxide catalysts showed a type 4 having pore range of 7-20 nm and BET surface area was increased from 17 to $205\;m^2{\cdot}g^{-1}$ with increasing of Mn content. The XPS analysis showed the surface oxidation state of Cu and Mn represented $Cu^{2+}$and the mixture of $Mn^{3+}$ and $Mn^{4+}$, respectively. Among the catalysts studied here, Cu/(Cu+Mn) = 0.5 catalyst showed the highest activity at $30^{\circ}C$ in CO oxidation and the catalytic activity showed a typical volcano-shape curve with respect to Cu/(Cu+Mn) molar ratios. The water vapor showed a prohibiting effect on the efficiency of the catalyst which is due to the competitive adsorption of carbon monoxide on the active sites of catalyst surface and finally the formation of hydroxyl group with active metals.

  • https://doi.org/10.7464/ksct.2010.16.2.132 인용 PDF KSCI