Comparison of two physical models for fitting PEM fuel cell impedance spectra measured at a low air flow stoichiometry

Local impedance spectra of a segmented PEM fuel cell operated at an air flow stoichiometry of λ = 2 are measured. The local spectra are fitted with the recent 1D and quasi–2D (q2D) physical models for PEMFC impedance. The q2D model takes into account oxygen transport in the gas channel, while the 1D model ignores this transport assuming infinite stoichiometry of the air flow. Analysis of the q2D expression for the GDL impedance Z∞gdl at λ → ∞ shows that the contribution of Z∞gdl to the total cell impedance rapidly decays with the frequency growth. We derive an equation for the boundary frequency flim, above which this contribution is small. We show that the 1D model can be fitted to the high–frequency part (f > flim) of a spectrum acquired at λ ≃ 2, ignoring the low–frequency arc due to the oxygen transport in the channel. Comparison of fitting parameters resulted from the 1D and q2D models confirms this idea

Fe/Co Alloys for the Catalytic Chemical Vapor Deposition Synthesis of Single- and Double-Walled Carbon Nanotubes (CNTs). 1. The CNT−Fe/Co−MgO System

Mg0.90FexCoyO (x + y ) 0.1) solid solutions were synthesized by the ureic combustion route. Upon reduction at 1000 °C in H2-CH4 of these powders, Fe/Co alloy nanoparticles are formed, which are involved in the formation of carbon nanotubes, which are mostly single and double walled, with an average diameter close to 2.5 nm. Characterizations of the materials are performed using 57Fe Mo¨ssbauer spectroscopy and electron microscopy, and a well-established macroscopic method, based on specific-surface-area measurements, was applied to quantify the carbon quality and the nanotubes quantity. A detailed investigation of the Fe/Co alloys’ formation and composition is reported. An increasing fraction of Co2+ ions hinders the dissolution of iron in the MgO lattice and favors the formation of MgFe2O4-like particles in the oxide powders. Upon reduction, these particles form R-Fe/Co particles with a size and composition (close to Fe0.50Co0.50) adequate for the increased production of carbon nanotubes. However, larger particles are also produced resulting in the formation of undesirable carbon species. The highest CNT quantity and carbon quality are eventually obtained upon reduction of the iron-free Mg0.90Co0.10O solid solution, in the absence of clusters of metal ions in the starting material. Introduction Catalyti

Fe-substituted mullite powders for the in situ synthesis of carbon nanotubes by catalytic chemical vapor deposition

Powders of iron-substituted mullite were prepared by combustion and further calcination in air at different temperatures. A detailed study involving notably Mo¨ssbauer spectroscopy showed that the Fe3+ ions are distributed between the mullite phase and a corundum phase that progressively dissolves into mullite upon the increase in calcination temperature. Carbon nanotube-Fe-mullite nanocomposites were prepared for the first time by a direct method involving a reduction of these powders in H2-CH4 and without any mechanical mixing step. The carbon nanotubes formed by the catalytic decomposition of CH4 on the smallest metal particles are mostly double-walled and multiwalled, although some carbon nanofibers are also observed

Influence of Carbon Supports on Palladium Nanoparticle Activity toward Hydrodeoxygenation and Aerobic Oxidation in Biomass Transformations

[EN] Three palladium catalysts at similar loadings supported on few-layers graphene (FLG), carbon nanotubes (CNT) and carbon nanofibers (CNF) have been prepared by wet impregnation of palladium nitrate with the purpose of determine the influence of the support on Pd catalytic activity. The supports and catalysts have been characterized by chemical analysis, Raman spectroscopy, XRD, electron microscopy and XPS. The average Pd particle size depends on the carbon support, ranging from 1.6 nm for CNF to 2.6 nm for FLG. The catalytic activity of these catalysts was evaluated for two different reactions of interest for biomass transformations, namely hydrodeoxygenation of vanillin to 2-methoxy-4-methyl-phenol (creosol) that requires a bifunctional catalyst with hydrogenating and Lewis acid sites, and aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid. Both compounds have application either as food flavouring additive and polyester co-monomer. For the two reactions the activity order of the fresh catalyst was Pd/FLG > Pd/CNF > Pd/CNT, indicating that FLG contributes favorably to the activity in spite of the larger Pd size of the nanoparticles on this support, a fact that has been attributed to the interaction with the prismatic planes on where Pd nanoparticles are located.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa GTQ2015-65163-C02-R1 and CTQ2014-53292-R) is gratefully acknowledged. Generalidad Valenciana is also thanked for funding (Prometeo 2017/063). S. N. thanks financial support by the Fundacion Ramon Areces (XVIII Concurso Nacional para la Adjudicacion de Ayudas a la Investigacion en Ciencias de la Vida y de la Materia, 2016). C. R. C. thanks CONICYT for the financial support (Becas de doctorado en el extranjero "Becas Chile" - no 72170200). The authors thank Dr. Tobias Placke (Universitat Munster, Germany) for nitrogen adsorption measurements and adsorptive potential distributions calculations.Espinosa-López, JC.; Castro Contreras, R.; Navalón Oltra, S.; Rivera-Cárcamo, C.; Alvaro Rodríguez, MM.; Machado, BF.; Serp, P.... (2019). Influence of Carbon Supports on Palladium Nanoparticle Activity toward Hydrodeoxygenation and Aerobic Oxidation in Biomass Transformations. European Journal of Inorganic Chemistry. (14):1979-1987. https://doi.org/10.1002/ejic.201900190S1979198714Corma, A., Iborra, S., & Velty, A. (2007). Chemical Routes for the Transformation of Biomass into Chemicals. Chemical Reviews, 107(6), 2411-2502. doi:10.1021/cr050989dHuber, G. W., Iborra, S., & Corma, A. (2006). Synthesis of Transportation Fuels from Biomass:  Chemistry, Catalysts, and Engineering. Chemical Reviews, 106(9), 4044-4098. doi:10.1021/cr068360dNavarro, R. M., Peña, M. A., & Fierro, J. L. G. (2007). Hydrogen Production Reactions from Carbon Feedstocks:  Fossil Fuels and Biomass. Chemical Reviews, 107(10), 3952-3991. doi:10.1021/cr0501994Chheda, J. N., Huber, G. W., & Dumesic, J. A. (2007). Liquid-Phase Catalytic Processing of Biomass-Derived Oxygenated Hydrocarbons to Fuels and Chemicals. Angewandte Chemie International Edition, 46(38), 7164-7183. doi:10.1002/anie.200604274Zhou, C.-H., Xia, X., Lin, C.-X., Tong, D.-S., & Beltramini, J. (2011). Catalytic conversion of lignocellulosic biomass to fine chemicals and fuels. Chemical Society Reviews, 40(11), 5588. doi:10.1039/c1cs15124jWildgoose, G. G., Banks, C. E., & Compton, R. G. (2006). Metal Nanoparticles and Related Materials Supported on Carbon Nanotubes: Methods and Applications. Small, 2(2), 182-193. doi:10.1002/smll.200500324Zhu, J., Holmen, A., & Chen, D. (2013). Carbon Nanomaterials in Catalysis: Proton Affinity, Chemical and Electronic Properties, and their Catalytic Consequences. ChemCatChem, 5(2), 378-401. doi:10.1002/cctc.201200471Calvo-Flores, F. G., & Dobado, J. A. (2010). Lignin as Renewable Raw Material. ChemSusChem, 3(11), 1227-1235. doi:10.1002/cssc.201000157Upton, B. M., & Kasko, A. M. (2015). Strategies for the Conversion of Lignin to High-Value Polymeric Materials: Review and Perspective. Chemical Reviews, 116(4), 2275-2306. doi:10.1021/acs.chemrev.5b00345Zhang, F., Jin, Y., Fu, Y., Zhong, Y., Zhu, W., Ibrahim, A. A., & El-Shall, M. S. (2015). Palladium nanoparticles incorporated within sulfonic acid-functionalized MIL-101(Cr) for efficient catalytic conversion of vanillin. Journal of Materials Chemistry A, 3(33), 17008-17015. doi:10.1039/c5ta03524dSantos, J. L., Alda-Onggar, M., Fedorov, V., Peurla, M., Eränen, K., Mäki-Arvela, P., … Murzin, D. Y. (2018). Hydrodeoxygenation of vanillin over carbon supported metal catalysts. Applied Catalysis A: General, 561, 137-149. doi:10.1016/j.apcata.2018.05.010Hao, P., Schwartz, D. K., & Medlin, J. W. (2018). Phosphonic acid promotion of supported Pd catalysts for low temperature vanillin hydrodeoxygenation in ethanol. Applied Catalysis A: General, 561, 1-6. doi:10.1016/j.apcata.2018.05.008Zhang, F., Zheng, S., Xiao, Q., Zhong, Y., Zhu, W., Lin, A., & Samy El-Shall, M. (2016). Synergetic catalysis of palladium nanoparticles encaged within amine-functionalized UiO-66 in the hydrodeoxygenation of vanillin in water. Green Chemistry, 18(9), 2900-2908. doi:10.1039/c5gc02615fDavis, S. E., Ide, M. S., & Davis, R. J. (2013). Selective oxidation of alcohols and aldehydes over supported metal nanoparticles. Green Chem., 15(1), 17-45. doi:10.1039/c2gc36441gZhang, Z., & Deng, K. (2015). Recent Advances in the Catalytic Synthesis of 2,5-Furandicarboxylic Acid and Its Derivatives. ACS Catalysis, 5(11), 6529-6544. doi:10.1021/acscatal.5b01491Teong, S. P., Yi, G., & Zhang, Y. (2014). Hydroxymethylfurfural production from bioresources: past, present and future. Green Chemistry, 16(4), 2015. doi:10.1039/c3gc42018cSiyo, B., Schneider, M., Radnik, J., Pohl, M.-M., Langer, P., & Steinfeldt, N. (2014). Influence of support on the aerobic oxidation of HMF into FDCA over preformed Pd nanoparticle based materials. Applied Catalysis A: General, 478, 107-116. doi:10.1016/j.apcata.2014.03.020Rathod, P. V., & Jadhav, V. H. (2018). Efficient Method for Synthesis of 2,5-Furandicarboxylic Acid from 5-Hydroxymethylfurfural and Fructose Using Pd/CC Catalyst under Aqueous Conditions. ACS Sustainable Chemistry & Engineering, 6(5), 5766-5771. doi:10.1021/acssuschemeng.7b03124Machado, B. F., Oubenali, M., Rosa Axet, M., Trang NGuyen, T., Tunckol, M., Girleanu, M., … Serp, P. (2014). Understanding the surface chemistry of carbon nanotubes: Toward a rational design of Ru nanocatalysts. Journal of Catalysis, 309, 185-198. doi:10.1016/j.jcat.2013.09.016Placke, T., Siozios, V., Schmitz, R., Lux, S. F., Bieker, P., Colle, C., … Winter, M. (2012). Influence of graphite surface modifications on the ratio of basal plane to «non-basal plane» surface area and on the anode performance in lithium ion batteries. Journal of Power Sources, 200, 83-91. doi:10.1016/j.jpowsour.2011.10.085Themed Issue: Lithium Ions in Solids - Between Basics and Better Batteries / Paul Heitjans. Zeitschrift für Physikalische ChemieReshetenko, T. V., Avdeeva, L. B., Ismagilov, Z. R., Pushkarev, V. V., Cherepanova, S. V., Chuvilin, A. L., & Likholobov, V. A. (2003). Catalytic filamentous carbon. Carbon, 41(8), 1605-1615. doi:10.1016/s0008-6223(03)00115-5Estrade-Szwarckopf, H. (2004). XPS photoemission in carbonaceous materials: A «defect» peak beside the graphitic asymmetric peak. Carbon, 42(8-9), 1713-1721. doi:10.1016/j.carbon.2004.03.005Ganesan, K., Ghosh, S., Gopala Krishna, N., Ilango, S., Kamruddin, M., & Tyagi, A. K. (2016). A comparative study on defect estimation using XPS and Raman spectroscopy in few layer nanographitic structures. 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Characterization and activity test of commercial Ni/Al2O3, Cu/ZnO/Al2O3 and prepared NieCu/Al2O3 catalysts for hydrogen production from methane and methanol fuels

In this study, methane and methanol steam reforming reactions over commercial Ni/Al2O3, commercial Cu/ZnO/Al2O3 and prepared NieCu/Al2O3 catalysts were investigated. Methane and methanol steam reforming reactions catalysts were characterized using various techniques. The results of characterization showed that Cu particles increase the active particle size of Ni (19.3 nm) in NieCu/Al2O3 catalyst with respect to the commercial Ni/ Al2O3 (17.9). On the other hand, Ni improves Cu dispersion in the same catalyst (1.74%) in comparison with commercial Cu/ZnO/Al2O3 (0.21%). A comprehensive comparison between these two fuels is established in terms of reaction conditions, fuel conversion, H2 selectivity, CO2 and CO selectivity. The prepared catalyst showed low selectivity for CO in both fuels and it was more selective to H2, with H2 selectivities of 99% in methane and 89% in methanol reforming reactions. A significant objective is to develop catalysts which can operate at lower temperatures and resist deactivation. Methanol steam reforming is carried out at a much lower temperature than methane steam reforming in prepared and commercial catalyst (275-325 o C). However, methane steam reforming can be carried out at a relatively low temperature on NieCu catalyst (600-650 o C) and at higher temperature in commercial methane reforming catalyst (700-800 o C). Commercial Ni/Al2O3 catalyst resulted in high coke formation (28.3% loss in mass) compared to prepared NieCu/Al2O3 (8.9%) and commercial Cu/ZnO/Al2O3 catalysts (3.5%).Web of Scienc

Optimization of the Perturbation Amplitude for Impedance Measurements in a Commercial PEM Fuel Cell Using Total Harmonic Distortion

One of the most important measurement parameters in electrochemical impedance spectroscopy (EIS) is the perturbation amplitude. The optimum perturbation amplitude value corresponds with a balance between the signal-to-noise ratio improvement and the reduction of the harmonic generation due to nonlinear effects. Therefore, the optimum perturbation amplitude is the maximum amplitude that ensures a linear response of the system. Two strategies were considered in this work, i.e., a constant amplitude strategy and a frequency dependent amplitude strategy. On the one hand, for the constant amplitude strategy, the optimum perturbation amplitude for EIS measurements of an individual cell of a commercial PEM fuel cell stack was determined. In order to fulfill this aim, the impedance spectra (at different DC currents) of the individual cell of the commercial PEM fuel cell stack were measured using different perturbation amplitudes. The total harmonic distortion of the recorded voltage signal was determined in each case, applying a FFT based method. The optimum amplitude for each DC current corresponds to the amplitude that minimizes the critical total harmonic distortion value. On the other hand, for the frequency dependent amplitude strategy, the optimum amplitude at each frequency for EIS measurements of an individual cell of a commercial PEM fuel cell stack was determined.Giner Sanz, JJ.; Ortega Navarro, EM.; Pérez Herranz, V. (2016). Optimization of the Perturbation Amplitude for Impedance Measurements in a Commercial PEM Fuel Cell Using Total Harmonic Distortion. Fuel Cells. 16(4):469-479. doi:10.1002/fuce.201500141S46947916