Electrocatalytic properties of the nanostructured electrodes and membranes in hydrogen-air fuel cells (original) (raw)
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Journal of Power Sources, 2009
The influence of low partial pressure of hydrogen on carbon nanofibers (CNFs) properties has been studied in the synthesis by methane catalytic decomposition, with the purpose of using them in polymer electrolyte fuel cells as electrocatalyst support. Using CNFs in this kind of application presents a good perspective to improve the fuel cell overall performance. CNF growth in the catalytic decomposition of methane and the characteristics which are typically required in a carbonaceous support, are influenced by hydrogen concentration, which has been studied at different temperatures. The textural, morphological and structural characteristics of the obtained CNFs have been determined by nitrogen physisorption, X-ray diffraction, electron microscopy and thermogravimetry. Electrical conductivity of CNFs has been measured compressing the powder and using a two-probe method. It was observed that low values of partial pressure of hydrogen in methane influence positively structural ordering of CNFs, and in turn improve electrical conductivity, with a slight influence on textural properties leading to highly mesoporous carbon.
International Journal of Hydrogen Energy, 2010
Novel carbonaceous supports for electrocatalysts are being investigated to improve the performance of polymer electrolyte fuel cells. Within several supports, carbon nanofibers blend two properties that rarely coexist in a material: a high mesoporosity and a high electrical conductivity, due to their particular structure. Carbon nanofibers have been obtained by catalytic decomposition of methane, optimizing growth conditions to obtain carbon supports with different properties. Subsequently, the surface chemistry has been modified by an oxidation treatment, in order to create oxygen surface groups of different nature that have been observed to be necessary to obtain a higher performance of the electrocatalyst. Platinum has then been supported on the as-prepared carbon nanofibers by different deposition methods and the obtained catalysts have been studied by different electrochemical techniques. The influence of carbon nanofibers properties and functionalization on the electrochemical behavior of the electrocatalysts has been studied and discussed, obtaining higher performances than commercial electrocatalysts with the highest electrical conductive carbon nanofibers as support.
Electrochemical stability of carbon nanofibers in proton exchange membrane fuel cells
Electrochimica Acta, 2011
This fundamental study deals with the electrochemical stability of several non-conventional carbon based catalyst supports, intended for low temperature proton exchange membrane fuel cell (PEMFC) cathodes. Electrochemical surface oxidation of raw and functionalized carbon nanofibers, and carbon black for comparison, was studied following a potential step treatment at 25.0 • C in acid electrolyte, which mimics the operating conditions of low temperature PEMFCs. Surface oxidation was characterized using cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Cyclic voltammograms clearly showed the presence of the hydroquinone/quinone couple. Furthermore, identification of carbonyl, ether, hydroxyl and carboxyl surface functional groups were made by deconvolution of the XPS spectra. The relative increase in surface oxides on carbon nanofibers during the electrochemical oxidation treatment is significantly smaller than that on carbon black. This suggests that carbon nanofibers are more resistant to the electrochemical corrosion than carbon black under the experimental conditions used in this work. This behaviour could be attributed to the differences found in the microstructure of both kinds of carbons. According to these results, carbon nanofibers possess a high potential as catalyst support to increase the durability of catalysts used in low temperature PEMFC applications.
Journal of Power Sources, 2009
Tubular carbon nanofibers with an average diameter of 150 nm are investigated as a possible material for the electrodes preparation for polymer electrolyte membrane fuel cells. Well-dispersed platinum particles with an average crystallite size of 4.6 nm are deposited on surface-oxidised fibers to be used as a catalyst support with an electroless plating method. The carbon nanofiber-based electrodes are prepared by a sedimentation method without the use of organic solvents. This method allows an exact setting of the fiber and binder content and the catalyst loading. The electrodes are optimised by varying the thickness of the gas diffusion layer and its binder content as well as the thickness of the active layer. These optimised electrodes show a considerably better performance when compared to carbon blackbased electrodes with the same catalyst loading prepared by a spraying process using the same type and amount of electrolyte in the membrane electrode assembly. By reducing the platinum content from 0.7 to 0.2 mg cm −2 , catalyst utilisation is significantly increased.
Applied Surface Science, 2014
A novel hybrid system has been investigated based on polyaniline/carbon nanofiber (Pani/CNF) electrospun nanofibers for modification of gas diffusion electrode (GDE) in proton exchange membrane fuel cells (PEMFC). Pani/CNF hybrid nanofibers were synthesized directly on carbon paper by electrospinning method. For preparation of catalyst ink, 20 wt.% Pt/C electrocatalyst with a platinum loading of 0.4 mg cm −2 was prepared by polyol technique. SEM studies applied for morphological study of the modified GDE with hybrid nanofibers. This technique indicated that the electrospun nanofibers had a diameter of roughly 100 nm. XRD patterns also showed that the average size of Pt nanoparticles was about 2 nm. Subsequently, comparison of the hybrid electrode electrochemical behavior and 20 wt.% Pt/C commercial one was studied by cyclic voltammetry experiment. The electrochemical data indicated that the hybrid electrode exhibited higher current density (about 15 mA cm −2) and ESA (160 m 2 gr −1) than commercial Pt/C with amount of about 10 mA cm −2 and 114 m 2 gr −1 , respectively. The results herein demonstrate that Pani/CNF nanofibers can be used as a good alternative electrode material for PEMFCs.
Particle/Polymer Nanofiber Mat Electrodes for Hydrogen/Air Fuel Cells
2016
Considerable efforts have been devoted to identifying new catalyst electrode materials for low Pt-loading fuel cells. One path leads through Pt alloys with non-noble metals and through core-shell nanostructures. An alternative approach to reduce the amount of Pt in a fuel cell without a loss in power output is through improvements in the cathode morphology to maximize catalyst contact with feed gases and enable facile water expulsion while maintaining a sufficient number of pathways for proton and electron conduction. Electrodes with such properties have been created by electrospinning. In this paper, our recent work on the electrospinning of particle/polymer nanofiber Pt/C electrodes is briefly summarized, with a focus on improving the performance of the oxygen cathode in a hydrogen/air PEM fuel cell. The effects of catalyst loading and binder composition (Nafion, Nafion/PVDF blends, and PVDF) on fuel cell power output and durability is discussed.
2011
For all the catalysts in this work, we have used commercially obtained carbon nanofiber (CNF) as the support material and iron acetate (FeAc) (Rankem), 1, 10-phenanthroline (phen) (Aldrich 99%) as the Fe and nitrogen precursors respectively. The surface area and average pore radius of the CNF are approximately 45 m 2 /g and 16 Å respectively as evident from the N 2 sorption studies (Fig. S13). In a typical synthesis of iron nitride-doped CNF (FeN x CNF), appropriate amount of CNF was dispersed in 50 ml of ethanol (Rankem 99.9%) by ultrasonication. An excess of phen was dissolved in 25 ml of ethanol and was allowed to fill the inner pore of CNF by magnetic stirring for about 30 min. Further the required amount of FeAc in ethanol was added drop by drop to phen in CNF mixture. The weight percentage of Fe was maintained about 0.5 %. The FeAc reacted with phen to form Fe [(phen) 3 ] 2+ chelate complex which was confirmed from the color change from pale yellow to wine red. Subsequently, the chelate
Arabian Journal of Chemistry, 2019
Doped graphene-based cathode catalysts are considered as promising competitors for ORR, but their power density has been low compared to Pt-based cathodes, mainly due to poor mass-transport properties. A new electrocatalyst for PEMFCs, an iodine doped grahene was prepared, characterized, and tested and the results are presented in this paper. We report a hybrid derived electrocatalyst with increased electrochemical active area and enhanced mass-transport properties. The electrochemical performances of several configurations were tested and compared with a typical Pt/C cathode configuration. As a standalone catalyst, the iodine doped graphene gives a performance with 60% lower than if it is placed between gas diffusion layer and catalyst layer. If it is included as microporous layer, the electrochemical performances of the fuel cell are with 15% bigger in terms of power density than the typical fuel cell with the same Pt/C loading, proving the beneficial effect of the iodine doped graphene for the fuel cell in the ohmic and mass transfer region. Moreover, the hybrid cathode manufactured by commercial Pt/C together with the material with best proprieties, is tested in a H 2-Air fuel cell and a power density of 0.55 W cm À2 at 0.52 V was obtained, which is superior to that of a commercial Pt-based cathode tested under identical conditions (0.46 W cm À2).
In this study, Co/CeO 2 decorated carbon nanofibers are introduced as effective electro-catalyst for methanol oxidation. Poly(vinyl alcohol) was used as carbon source due to its high carbon content characteristic as compared to many others polymer precursors for CNFs synthesis. Preparation of the introduced nanofibers could be achieved by calcination of electrospun nanofibers composed of cerium (III) acetate hydrate, cobalt (II) acetate tetra hydrate and poly(vinyl alcohol) in nitrogen environment at 700 1C. The produced sintered powder was characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), field-emission scanning electron microscopy (FESEM) equipped with rapid EDX (energy dispersive analysis of X-ray). The invoked characterization techniques indicated that the obtained material is carbon nanofibers decorated by Co/CeO 2 nanoparticles. Investigation of the electrocatalytic activity of the introduced decorated nanofibers toward methanol oxidation indicated good performance as the corresponding current density increased with increasing methanol content in the alkaline medium. Interestingly, the introduced catalyst revealed negative onset potential ( À50 mV vs. Ag/AgCl) which is a superior value among the reported non-precious electrocatalyst. Moreover, methanol oxidation takes place at relatively low applied voltage (180 mV vs. Ag/AgCl) which adds additional advantage for the introduced material. Overall, the introduced study opens new avenue for cheap and effective transition and rare earth family-based nanomaterials as non-precious catalyst for fuel cell application.