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International journal of hydrogen energy 51건

  1. [해외논문]   A three-dimensional model for transient performance of a solid oxide fuel cell   SCI SCIE

    Ho, T.X.
    International journal of hydrogen energy v.39 no.12 ,pp. 6680 - 6688 , 2014 , 0360-3199 ,

    초록

    This paper presents an analysis of transient behavior of an anode-supported solid oxide fuel cell (SOFC) using a model, which has recently been built for steady state operation. The model is three dimensional (3D), which takes into account heat and mass transport, chemical and electrochemical reactions taking place simultaneously in the cell. The electrochemical processes are assumed to take place in a layer of finite thickness at electrode-electrolyte interfaces. A repeating unit of a planar anode-supported SOFC with co-flow configuration is investigated. Step changes of working voltage and fuel composition are applied to the cell. Results for the dynamic profiles of the temperature, the current density and the activation overpotential distributions in the cell are presented and discussed.

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  2. [해외논문]   Overview on the developments of vapor-feed direct methanol fuel cells   SCI SCIE

    Yuan, W. , Zhou, B. , Deng, J. , Tang, Y. , Zhang, Z. , Li, Z.
    International journal of hydrogen energy v.39 no.12 ,pp. 6689 - 6704 , 2014 , 0360-3199 ,

    초록

    Direct methanol fuel cells have attracted extensive attentions from the fuel cell community because it is regarded as a promising candidate to replace the traditional power sources for portable applications. This technical review specially summarizes the development of the vapor-feed direct methanol fuel cell (VF-DMFC) which exhibits diverse characteristics from the liquid-feed system. This work is to provide a technical reference for engineering practice in the field of the VF-DMFC. Details concerning the system design and operation of active, semi-passive and fully-passive VF-DMFCs are provided. As a special subclass, the situation of high-temperature VF-DMFC is also introduced in this work. For the VF-DMFCs, several primary issues such as methanol, water and product managements and electrode optimization are respectively analyzed. Along with this, the mechanisms and strategies for optimization of each issue are remarked. Considering the significance and contribution of modeling works, such information is individually reviewed. Based on an overall evaluation, the emphases of the future work are also discussed.

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  3. [해외논문]   Electrocatalytic oxidation of methanol on CoNi electrodeposited materials   SCI SCIE

    Tarrus, X. , Montiel, M. , Valles, E. , Gomez, E.
    International journal of hydrogen energy v.39 no.12 ,pp. 6705 - 6713 , 2014 , 0360-3199 ,

    초록

    Cobalt-nickel bimetallic materials electrodeposited on Si/Ti/Ni substrates were evaluated for the oxidation of methanol in alkaline media. CoNi samples were prepared potentiostatically selecting conditions adequate to achieve the desired Co/Ni ratio. All samples were characterized by X-ray fluorescence and cyclic voltammetry to determine their composition and electrochemical behaviour. The electrocatalytical performance of prepared samples was evaluated also by cyclic voltammetry using methanol solutions in alkaline media. Material composition, methanol and NaOH concentration, and temperature were the variables studied. The results indicate that a cobalt excess inhibits the methanol oxidation. In the same way, a significant enhancement of the oxidation current was observed on increasing the NaOH concentration up to 0.5 M, but for higher concentrations the electrocatalytic performance of these materials decreases. With regard to the increase of MeOH concentration or temperature, both variables are related to an improvement of the electrocatalytic performance. Finally, the effect of platinum skin on the CoNi deposits was evaluated, concluding that it favours MeOH oxidation but does not protect the substrate surface from the damage exerted by excessive NaOH concentration.

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  4. [해외논문]   Study on the levelling process of the current collector for the molten carbonate fuel cell based on curvature integration method   SCI SCIE

    Lee, C.W. , Yang, D.Y. , Kang, D.W. , Lee, T.W.
    International journal of hydrogen energy v.39 no.12 ,pp. 6714 - 6728 , 2014 , 0360-3199 ,

    초록

    The current collector for the molten carbonate fuel cell (MCFC) is manufactured from the sheet metal forming process. After the forming process, the current collector is bent resulting in a specific curvature (κ i ) in the direction in which trapezoidal protrusions are formed due to springback. In the stack of the MCFC, small deformation of the current collector can bring about defects in the electrolyte, non-uniform contact and difficulties in assembling the stack. Therefore, the curvature of the current collector should be minimized in order to reduce defects which can cause critical damage in the long-term operation. In order to straighten the current collector, the levelling process using three rolls was employed. In this work, a simple and effective method for designing the levelling process was proposed. An analytic model and the finite element analysis were used in combination. The optimal curvature minimizing the resultant curvature and the resultant moment of the current collector down to zero was calculated from the bending moment-curvature relationship. The bending moment-curvature relationship of the current collector was determined from the finite element analysis of uniform bending using the simulation results of the three-stage forming process. In the analytic model based on curvature integration method, the proper roll arrangement corresponding to the optimal curvature was calculated. Experiments were conducted using the calculated roll arrangement. The current collector was levelled nearly flat using the levelling process. After the levelling process, the flattened current collector was easily assembled with a centre plate and ensuring uniform contact with the electrolyte.

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  5. [해외논문]   Preparation and characterization of nanoporous carbon-supported platinum as anode electrocatalyst for direct borohydride fuel cell   SCI SCIE

    Liu, J. , Wang, H. , Wu, C. , Zhao, Q. , Wang, X. , Yi, L.
    International journal of hydrogen energy v.39 no.12 ,pp. 6729 - 6736 , 2014 , 0360-3199 ,

    초록

    The nanoporous carbon (NPC) is synthesized by carbonization of metal-organic framework-5 (MOF-5, [Zn 4 O(bdc) 3 ], bdc = 1,4-benzenedicarboxylate) with furfuryl alcohol (FA) as carbon source and used as the carrier of the anode catalyst for the direct borohydride-hydrogen peroxide fuel cell (DBHFC). Then the NPC-supported Pt anode catalyst (Pt/NPC) is firstly prepared by a modified NaBH 4 reduction method. The obtained Pt/NPC catalyst is characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), cyclic voltammetry, chronopotentiometry, chronoamperometry and fuel cell test. The results show that the Pt/NPC is made up of the spherical Pt nanoparticles which disperse uniformly on the surface of the NPC with average size 2.38 nm, and exhibits 36.38% higher current density for directly borohydride oxidation than the Vulcan XC-72 carbon supported Pt (Pt/XC-72). Besides, the DBHFC using the Pt/NPC as anode electrocatalyst shows the maximum power density as high as 54.34 mW cm -2 at 25 o C.

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  6. [해외논문]   Selective adsorption of tert-butylmercaptan and tetrahydrothiophene on modified activated carbons for fuel processing in fuel cell applications   SCI SCIE

    Ho, P.H. , Lee, S.Y. , Lee, D. , Woo, H.C.
    International journal of hydrogen energy v.39 no.12 ,pp. 6737 - 6745 , 2014 , 0360-3199 ,

    초록

    The effects of surface oxidation and KOH impregnation on activated carbon for the selective adsorption of tert-butylmercaptan (TBM) and tetrahydrothiophene (THT) present in natural fuel gas were studied. Physicochemical properties of the adsorbents were characterized by N 2 adsorption, X-ray diffraction (XRD), temperature programmed desorption (TPD), scanning electron microscopy (SEM), and surface pH measurements. Oxidation treatments by HNO 3 or H 2 O 2 gave rise to considerable increases in both TBM and THT adsorption capacity, about a threefold enhancement from those on pristine activated carbon. Notably, it was found that the oxidative modifications led to an enhancement in THT adsorption selectivity, whereas KOH impregnation led to a marked increase in TBM adsorption selectivity. The properties of the adsorption sites and the adsorption strength of TBM and THT on the sites were characterized. These results agree well with the experimental sulfur adsorption capacities of the samples and can be explained by an adsorption model proposed in this work.

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  7. [해외논문]   Effects of H2 on the number concentration of particulate matter in diesel engines using a low-pressure loop exhaust-gas recirculation system   SCI SCIE

    Cho, Y. , Song, S. , Chun, K.M.
    International journal of hydrogen energy v.39 no.12 ,pp. 6746 - 6752 , 2014 , 0360-3199 ,

    초록

    We investigated the effects of H 2 on the number concentration of particulate matter (PM) emissions from a diesel engine fitted with a low-pressure loop exhaust gas recirculation system. We used a 2.2-L four-cylinder direct-injection diesel engine satisfying EURO V regulations, and converted this engine to include an H 2 feed. The air/fuel (A/F) ratio was varied in the range of 21.9-45.5 and the brake mean effective pressure was varied in the range of 2-6 bars to control the O 2 concentration and in-cylinder temperature, both of which are significant for PM emissions. The number concentration of the emitted PM was measured using a scanning mobility particle sizer. We found that the emitted PM decreased by the addition of H 2 which caused the unburned gas temperature increased. Furthermore, the degree of reduction was larger as the A/F ratio, load, and H 2 energy fraction increased. However, with A/F ratios of less than 21.9, the addition of H 2 increased the number concentration of emitted PM which was attributed to the small O 2 concentration at these A/F ratios.

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  8. [해외논문]   Hydrogen-enriched non-premixed jet flames: Analysis of the flame surface, flame normal, flame index and Wobbe index   SCI SCIE

    Ranga Dinesh, K.K.J. , Jiang, X. , van Oijen, J.A.
    International journal of hydrogen energy v.39 no.12 ,pp. 6753 - 6763 , 2014 , 0360-3199 ,

    초록

    A non-premixed impinging jet flame is studied using three-dimensional direct numerical simulation with detailed chemical kinetics in order to investigate the influence of fuel variability on flame surface, flame normal, flame index and Wobbe index for hydrogen-enriched combustion. Analyses indicate that the fuel composition greatly influences the H 2 /CO syngas combustion, not only on the important local stoichiometric iso-mixture fraction surface distribution but also on the vortical structures in the flow field. As a result of CO addition to hydrogen-rich combustion, changes of the reaction zone in the flammable layer, shift of peak flame surface density distribution, shift of non-premixed regions, formation of widely populated scalar dissipation distribution rate with respect to tangential strain and reduction of global heat release are all found to appear. In particular, the CO addition induces a micromixing process which appears to be an important factor for the modelling investigation of turbulence/chemistry interaction especially for combustion modelling of H 2 -rich syngas fuels.

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  9. [해외논문]   The features of ignition and combustion of composite propane-hydrogen fuel: Modeling study   SCI SCIE

    Titova, N.S. , Kuleshov, P.S. , Favorskii, O.N. , Starik, A.M.
    International journal of hydrogen energy v.39 no.12 ,pp. 6764 - 6773 , 2014 , 0360-3199 ,

    초록

    The extensive numerical analysis of the features of self ignition and formation of NO and CO during combustion of blended fuel, consisting of propane and hydrogen, with air is considered on the basis of extended detailed kinetic model involving both high and low temperature submechanisms of propane oxidation. It has been shown that for the blended C 3 H 8 -H 2 fuel there exists the temperature region, where the ignition of the C 3 H 8 -H 2 -air mixture occurs faster compared to pure propane. However, this region is not broad enough and has low and high temperature boundaries (T b and T h , respectively). At the initial temperature of fuel-air mixture T 0 b , the induction time of blended C 3 H 8 -H 2 fuel is greater than that of pure propane and, at T 0 > T h , the admixture of a small amount of propane (1 ~ 5% per volume) to hydrogen accelerates the ignition. The values of T b and T h depend on the composition of blended fuel and initial pressure. It has been revealed that the addition of hydrogen to propane increases the flame speed and extends the flammability thresholds both in fuel-lean and in fuel-rich regions, but doesn't result in the substantial change of the concentrations of main pollutants NO and CO in the combustion exhaust. However, the addition of hydrogen to fuel-lean propane-air mixture allows one to provide the stable combustion of leaner fuel-air mixture and, thus, to reduce notably the emission of NO and CO compared to that for the combustion of pure propane-air mixture.

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  10. [해외논문]   Influence of initial pressure and temperature on flammability limits of hydrogen-air   SCI SCIE

    Liu, X. , Zhang, Q.
    International journal of hydrogen energy v.39 no.12 ,pp. 6774 - 6782 , 2014 , 0360-3199 ,

    초록

    This paper presents data on the lower and upper flammability limits of hydrogen-air mixtures at elevated temperature and pressure. A 5-L explosion vessel, an ignition system, and a transient pressure measurement sub-system were used in this study. Through a series of experiments carried out, the lower and upper flammability limits of hydrogen-air mixtures at different initial pressures and temperatures have been studied and the influence of initial temperature and pressure on the lower and upper flammability limits of hydrogen-air mixtures has been analysed and discussed. It was found that the decrement of the LFLs of hydrogen-air with the initial temperature from 21 to 90 o C at the initial pressure of 0.1 MPa is less than 1%, the decrement of the LFLs with the initial temperature from 21 to 90 o C at 0.2 MPa is less than 1%, the decrement of the LFLs with the initial temperature from 21 to 90 o Cat 0.3 MPa is less than 0.66%, and the decrement of the LFLs with the initial temperature from 21 to 90 o C at 0.4 MPa is less than 0.25%. The lower flammability limits of hydrogen-air mixtures at the pressures of 0.1 and 0.4 MPa are 4 and 1.25%(V/V), respectively. The upper flammability limits of the hydrogen-air mixtures increase with the initial pressure and temperature. The upper flammability limit of the hydrogen-air mixtures at 90 o C and 0.4 MPa reaches 93%(V/V) which is much higher than that (76%(V/V)) at 21 o C and 0.1 MPa.

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