CaSO4 기반 산소전달입자의 환원과 분해특성

류호정,김하나,이동호,진경태,백점인 한국수소및신에너지학회 2015 한국수소 및 신에너지학회논문집 Vol.26 No.6

As a candidate for cheap oxygen carrier, CaSO4 based oxygen carriers have been developing. However, research on reaction characteristics and side reaction of CaSO4 based oxygen carrier is very limited. There are many possible reactions for main components of syngas from coal. In this study, we prepared three CaSO4 based oxygen carriers (CaSO4-Fe2O3/bentonite, CaSO4-K2CO3/bentonite, CaSO4-CaO/bentonite) and performed reduction tests by hydrogen. Cyclic reduction-oxidation tests up to 5 th cycle are also conducted using hydrogen as fuel. Reduction reactivity of those CaSO4 based oxygen carriers were compared with that of NiO based oxygen carrier (OCN703-1100). Real weight change fractions of CaSO4 based oxygen carriers were higher than theoretical oxyen transfer capacity and reactivity of these particles decreased with the number of cycle increased. To check possible side reaction of CaSO4 based oxygen carriers, CaSO4 decomposition tests were carried out and SO2 was detected even at 700°C. Consequently, we could conclude that CaSO4 based oxygen carriers decompose and release SO2 and this reaction lead reactivity decay of CaSO4 based oxygen carries.

Electrochemical Cr(VI) reduction using a sacrificial Fe anode: Impacts of solution chemistry and stoichiometry

Chuang, Sheng-Ming,Ya, Vinh,Feng, Chiao-Lin,Lee, Shou-Jen,Choo, Kwang-Ho,Li, Chi-Wang Elsevier 2018 Separation and purification technology Vol.191 No.-

<P><B>Abstract</B></P> <P>A systematic investigation of Cr(VI) reduction using electrochemical reduction revealed that the Cr(VI) reduction was extremely fast with reaction kinetics limited by the anodic generation of Fe(II). The Cr(VI) reduction rate increased with decreasing pH at the initial stage of reaction but the time to reach complete Cr(VI) reduction is pH independent. The amount of Fe(II) generated per mole of Cr(VI) reduced was calculated and compared with the stoichiometric value, i.e., 3mole of Fe(II) needed per mole of Cr(VI) reduced. The values are 11.1% higher than the stoichiometric value for pH 7 and 9, but are 32.0% less for pH 3 and 5. The spontaneous reduction of Cr(VI) by Fe<SUP>0</SUP> and adsorption of Cr(VI) to Fe(OH)<SUB>3</SUB> precipitates might contribute the additional Cr(VI) removal. Effect of DO was investigated under various mixing schemes. Under N<SUB>2</SUB> purging, Fe(II) generated for one mole of Cr(VI) reduced is 3.67% higher than the stoichiometric value, while mechanic mixing and aeration mixing show 15% and 19%, respectively, higher than stoichiometric value, indicating that DO does impact Cr(VI) reduction. The electrochemical Cr(VI) reduction process was also employed to treat electroplating wastewater with and without pH pre-adjustment, achieving 100% total Cr and Ni removal for both cases. ORP can be used as a controlling parameter when electrochemical reduction is implemented for Cr(VI) reduction.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effect of current on Cr(VI) reduction under same current density was studied. </LI> <LI> Effects of initial and fixed pH on Cr(VI) reduction were investigated. </LI> <LI> Effect of DO on Cr(VI) reduction was explored. </LI> <LI> Electrochemical reduction was applied for treating electroplating wastewater. </LI> <LI> ORP is an ideal parameter for controlling electrochemical Cr(VI) reduction. </LI> </UL> </P>

Phenyl Porphyrin 착물들이 수식된 유리질 탄소 전극에서 산소 환원에 대한 촉매 효과

노선균 ( Seon Gyun Rho ),한신 ( Shin Han ),박경희 ( Kyung Hee Park ) 조선대학교 공학기술연구원 2013 공학기술논문지 Vol.6 No.4

The electrocatalytic effect of oxygen reduction was investigated at glassy carbon electrode coated with metal(II) phenyl porphyrin complexes ; Co(II)(TMPP), Fe(II)(TMPP), Co(II)(TSPP), Fe(II)(TOAPP) in the 1 M KOH solution. The reduction current of oxygen measured by cyclic voltammetry was increased by about 200 % more than that of bare glassy carbon electrode and the reduction potential was shifted about 50 mV to the positive direction at glassy carbon electrode modified with metal(II) phenyl porphyrin complexes. The reduction current of oxygen was increased by raising scan rate and reduction potential was shifted to the negative potential direction. Also these reactions were proceed to diffusion controlled. According to raising temperature, the reduction current was increased and the reduction potential was shifted to the positive potential evaluated by determining cyclic voltammetry. The activation energy calculated by Arrhenius plot was 2.26 Kcal/mole at the catalyst modified electrode coated with Co(II)(TMPP) and 1.76 Kcal/mole at the catalyst modified electrode coated with Fe(II)(TOAPP) which was less than that of at the bare glassy carbon electrode, 3.27 kcal/mole. As a result, we can conclude that Co(II)(TMPP) and Fe(II)(TOAPP) complexes behaved as catalyst in the reductin reaction of oxygen.

Thermodynamic Evaluation of Oxygen Behavior in Ti Powder Deoxidized by Ca Reductant

Sun-Joong Kim,Jung-Min Oh,Jae-Won Lim 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.4

To produce low oxygen Ti powder of less than 1000 mass ppm, commercial Ti powder was deoxidized by two types of Ca reductants: a solid Ca and a Ca vapor. Compared with the iso-oxygen partial pressure in the Ti-O binary phase diagram, the PO2 in the raw Ti powder increased with temperature compared to the reduction reaction of Ca. Therefore, the O2 content in the Ti powder decreased as the deoxidation temperature increased from 873 K, showing a local minima at 1273 K. The oxygen concentration at 1373 K was greater than that at 1273 K because the oxygen solubility of the Ti powder was increased by the equilibrium relation between Ca and CaO. On the basis of the thermodynamic assessment, the deoxidation of Ti powder can be improved by increasing the temperature and lowering the oxygen solubility with the saturation of CaO.

Effect of electrochemical reduction on the structural and electrical properties of anodic TiO2 nanotubes

Muhammad Asim Rasheed,Kamran Ahmad,Nilem Khaliq,Yaqoob Khan,Muhammad Aftab Rafiq,Abdul Waheed,Attaullah Shah,Arshad Mahmood,Ghafar Ali 한국물리학회 2018 Current Applied Physics Vol.18 No.3

The effect of electrochemical reduction on the structural and electrical properties of amorphous as well as annealed TiO2 nanotubes (TNTs) is investigated under ambient conditions. TNTs were prepared by anodizing titanium sheet in ethylene glycol electrolyte containing NH4F and de-ionized water at 40 V for 6 h. Electrochemical reduction is carried out in 1 M aqueous KOH solution for ~15 s at 3 V. TNTs are characterized by SEM, XRD, XPS and impedance spectrometer. XRD results confirm an increase in dspacing for (101) and (200) planes, after electrochemical reduction. XPS data reveal that electrochemical reduction produced prominent shifts of ~0.7e1.0 eV in the binding energies of TNTs. Interestingly, these shifts recover completely (in case of amorphous TNTs) and partially (in case of anatase TNTs) within ~7 days after reduction process due to oxygen uptake. Partial recovery in the binding energies of anatase TNTs is due to the fact that the oxygen vacancies are thermodynamically more stable as compared to amorphous TNTs. Similarly, the electrochemical reduction process decreases the impedance values of TNTs by more than three orders of magnitudes (from MU to kU). The impedance values also recover to the similar values before reduction in a span of ~7days.

V₂O₅/TiO₂ 촉매의 선택적 환원촉매반응에서 격자산소의 역할

하헌필,최희락,Ha, Heon-Phil,Choi, Hee-Lack 한국재료학회 2006 한국재료학회지 Vol.16 No.5

In situ electrical conductivity measurements on $V_2O_5WO_3/TiO_2$ catalysts were carried out at between 100 and $300^{\circ}C$ under pure oxygen, NO and $NH_3$ to investigate the reaction mechanism for ammonia SCR (selective catalytic reduction) de NOX. The electrical conductivity of catalysts changed irregularly with supply of NO. It was, however, found that the electrical conductivity change with ammonia supply was regular and the increase of electrical conductivity was mainly caused by reduction of the labile surface oxygen. The electrical conductivity change of catalysts showed close relationship with the conversion rate of NOx. Variation of conversion rate in atmosphere without gaseous oxygen also showed that labile lattice oxygen is indispensable in the initial stage of the de NOx reaction. These results suggest that liable lattice oxygen acts decisive role in the de NOx mechanism. They also support that de NOx reaction occurs through the Eley?Rideal type mechanism. The amount of labile oxygen can be estimated from the measurement of electrical conductivity change for catalysts with ammonia supply. This suggests that measurement of the change can be used as a measure of the de NOx performance.

매체순환식 가스연소기용 산소공여입자들의 환원반응성에 미치는 CO₂ 농도의 영향

류호정,김홍기,박문희,이승용 한국수소및신에너지학회 2009 한국수소 및 신에너지학회논문집 Vol.20 No.3

Effect of CO2 concentration on reduction reactivity of oxygen carrier particles for chemical-looping combustor were investigated. Four particles, NiO/bentonite, OCN601-650, OCN702-1100, OCN702-1250, were used as oxygen carrier particles and two kinds of gases (CH4 5%, N2 balance and CH4 5%, CO2 balance) were used as reactants for reduction. For all oxygen carrier particles, higher maximum conversion, reduction rate, oxygen transfer capacity, and oxygen transfer rate were achieved when we used N2 balance gas. OCN601-650 particle showed higher oxygen transfer rate for all gases than other particles, and therefore we selected OCN601-650 particle as the best candidate. For all particles, lower carbon depositions were observed when we used CO2 balance gas.

The plasma-assisted formation of Ag@Co₃O₄ core-shell hybrid nanocrystals for oxygen reduction reaction

Kim, Sung-Min,Jo, Yu-Geun,Lee, Min-Hyung,Saito, Nagahiro,Kim, Jung-Wan,Lee, Sang-Yul Elsevier 2017 ELECTROCHIMICA ACTA Vol.233 No.-

<P><B>Abstract</B></P> <P>In this study, Ag@Co<SUB>3</SUB>O<SUB>4</SUB> core-shell hybrid nanocrystals are synthesized using a plasma discharge in water for oxygen reduction reaction in alkaline solutions. A detailed analysis via electron microscopy in combination with EDS elemental mapping conclusively verifies that the reactive oxygen species generated from the plasma-assisted decomposition of water molecules govern the phase structure of the nanocrystals. Under oxidizing conditions, the Co oxide, which is more stable than the Ag oxide, provides the driving force for the segregation and preferential oxidation of Co at the surface. This leads to the formation of the core-shell architecture. The electrochemical measurements for the oxygen reduction reaction reveal that the specific activities of the Ag@Co<SUB>3</SUB>O<SUB>4</SUB> core-shell nanocrystals are <I>ca</I>. 5.2 and 2.6 times higher than those of the pure Ag and Ag-Co alloy nanocrystals. The enhanced catalytic performance is attributed to the combination of electronic and geometric effects, which facilitates the OO bond breaking and desorption for the oxygen reduction. The insights gain through this study may serve as a foundation to design better electrochemical oxygen reduction electrocatalysts.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ag@Co<SUB>3</SUB>O<SUB>4</SUB> core-shell hybrid nanocrystal was formed via plasma discharge in water. </LI> <LI> The electronic structure of Ag@Co<SUB>3</SUB>O<SUB>4</SUB> core-shell hybrid nanocrystal was modified. </LI> <LI> Ag@Co<SUB>3</SUB>O<SUB>4</SUB> core-shell hybrid nanocrystals showed the best ORR activities. </LI> <LI> ORR was enhanced due to the combination of electronic and geometric effects. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

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.

Oxygen-Induced Residual Stress Reduction of Cubic Boron Nitride Films: Reinterpretation of Ye’s Results Considering Interfacial Turbostratic Boron Nitride Layer

Young‑Hwan Choi,Joo‑Youl Huh,Young‑Joon Baik 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.2

The effective residual stress reduction in a cubic boron nitride (cBN) thin film by the addition of oxygen gas is reported. Typically, a turbostratic BN layer (tBN) deposits on the substrate surface prior to a cBN layer. This interfacial tBN layer hasbeen observed that the addition of oxygen increases the thickness of the tBN layer, which is also a factor in reducing theresidual stress. In this study, the cBN and tBN layers are analysed to assess their individual effect on residual stress reductionwhen oxygen is added. The variation in residual stress in relation to the tBN layer thickness is estimated using data reportedpreviously by Ye et al. The estimated data shows that the reduction in the residual stress of the cBN layer is significantlygreater than that caused by an increase in the tBN layer thickness. This result shows that the residual stress of the cBN layercan be significantly reduced by the addition of oxygen.