Maryam Borghei - Academia.edu (original) (raw)

Papers by Maryam Borghei

Research paper thumbnail of CO-free Hydrogen production via Decomposition of Methane over Co-Mo-MgO Catalysis

Conventional processes for the production of hydrogen such as partial oxidation or steam reformin... more Conventional processes for the production of hydrogen such as partial oxidation or steam reforming of natural gas are multi-stage and complex which emit large amounts of CO 2 . Thermocatalytic decomposition (TCD) of methane is a potential route to production of CO-free hydrogen which can be directly entered to the fuel cells. The valuable by-product, pure carbon, is also formed which can extremely reduce the net cost of the process. In this work the TCD of methane over the Co-Mo-MgO catalyst at 900˚C was carried out in a fixed bed reactor and the exit gas of the reactor was analyzed by GC. The conversion of methane decomposition showed high value at the beginning. However, it gradually decreased with the time on stream. It is due to the formation of encapsulating carbon on the active metal sites which deactivates the catalyst during the time. The detailed description of the metal-catalyzed methane decomposition mechanism has been discussed in this paper.

Research paper thumbnail of Flexible metal-free counter electrode for dye solar cells based on conductive polymer and carbon nanotubes

Journal of electroanalytical chemistry

The counter electrodes (CEs) for flexible dye solar cells (DSCs) are normally prepared by sputter... more The counter electrodes (CEs) for flexible dye solar cells (DSCs) are normally prepared by sputtering platinum on indium tin oxide (ITO) plastic substrate. However both ITO and platinum are expensive materials that need to be replaced with cheaper alternatives in large scale production of low-cost DSCs. We fabricated a flexible and completely carbon-based CE for DSCs based on electropolymerized poly (3,4-ethylenedioxythiophene) (PEDOT) on single-walled carbon nanotube (SWCNT) film on a plain plastic substrate. The DSCs with such a CE had an efficiency of 4.0%, which is similar to the efficiency of the reference DSCs (3.9%) based on conventional sputtered platinum on ITO-plastic CE. The carbon-based electrode was prepared by a simple press-transfer method of SWCNTs from the collection filter used in the gas phase synthesis and by electrochemical deposition of PEDOT on it. Electrochemical impedance spectroscopy confirmed that the PEDOT–SWCNT film had the best catalytic performance amon...

Research paper thumbnail of Highly efficient cathode catalyst layer based on nitrogen-doped carbon nanotubes for the alkaline direct methanol fuel cell

Applied Catalysis B: Environmental, 2014

The performance of a direct methanol alkaline anion-exchange membrane (Fumatech FAA3) fuel cell w... more The performance of a direct methanol alkaline anion-exchange membrane (Fumatech FAA3) fuel cell with Pt-free nitrogen-doped few-walled carbon nanotubes (N-FWCNT) as the cathode catalyst is compared with a commercial supported Pt catalyst. The ionomer content of the N-FWCNT cathode catalyst layer is therefore optimized and it is shown to be 40 wt% of FAA3. Scanning electron microscopy images of the catalyst layer show that the ionomer forms aggregates with N-FWCNTs probably due to their charged nature and that the catalyst layer structure is remarkably open even with high ionomer contents facilitating the mass transfer of reactants and products to the active sites. With oxygen as the oxidant, the maximum power density obtained with our Pt-free N-FWCNTs (0.78 mW cm −2 ) is slightly higher than with the Pt catalyst (0.72 mW cm −2 ). However, when more practical air is used as the oxidant, the N-FWCNTs (0.73 mW cm −2 ) show clearly superior performance compared to the Pt catalyst (0.18 mW cm −2 ). The lower performance with the Pt catalyst is attributed to the denser electrode layer structure resulting in higher mass transport resistance and to the presence of methanol in the cathode, which poisons the Pt but not the N-FWCNTs.

Research paper thumbnail of Activity and stability studies of platinized multi-walled carbon nanotubes as fuel cell electrocatalysts

Applied Catalysis B: Environmental, 2015

Research paper thumbnail of Nitrogen-doped graphene with enhanced oxygen reduction activity produced by pyrolysis of graphene functionalized with imidazole derivatives

International Journal of Hydrogen Energy, 2014

Electrocatalyst Oxygen reduction reaction a b s t r a c t Nitrogen-doped graphene nanoplatelets (... more Electrocatalyst Oxygen reduction reaction a b s t r a c t Nitrogen-doped graphene nanoplatelets (N-GNP) with 1.6e3.3 at.% nitrogen content were synthesized by thermal annealing of GNP functionalized with a series of imidazole-based nitrogen-containing precursors of different nature, charge and nitrogen content. The imidazole derivatives included one ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4) and two polymers, a neutral one, poly(vinylimidazole) (PVI) and a poly(ionic liquid), poly(3-butyl-1-vinylimidazolium bromide) (PBVIBr). N-GNP showed enhanced electrocatalytic activity for oxygen reduction reaction (ORR) in alkaline media compared to pristine GNP, with the number of electrons transferred in oxygen-saturated KOH at low overpotentials following the trend: 2.5 (pristine GNP) < 2.9 (N-GNP from PVI eGNP) < 3.3 (N-GNP from BMIBF 4 eGNP) < 3.5 (N-GNP from PBVIBr-GNP). Interestingly, ORR catalytic activity did not correlate with total nitrogen content but was more affected by BrunauereEmmetteTeller (BET) surface area. The most active materials were N-GNP with lowest doping levels and highest surface area resulting from the ionic (imidazolium-based) nitrogen precursors.

Research paper thumbnail of Graphitized carbon nanofiber–Pt nanoparticle hybrids as sensitive tool for preparation of screen printing biosensors. Detection of lactate in wines and ciders

Bioelectrochemistry, 2015

This work describes the fabrication of a new lactate biosensor. The strategy is based on the use ... more This work describes the fabrication of a new lactate biosensor. The strategy is based on the use of a novel hybrid nanomaterial for amperometric biosensors i.e. platinum nanoparticles (PtNps) supported on graphitized carbon nanofibers (PtNps/GCNF) prepared by chemical reduction of the Pt precursor at GCNF surfaces. The biosensors were constructed by covalent immobilization of lactate oxidase (LOx) onto screen printed carbon electrodes (SPCEs) modified with PtNps (PtNps/GCNF-SPCEs) using polyethyleneimine (PEI) and glutaraldehyde (GA). Experimental variables concerning both the biosensor design and the detection process were investigated for an optimal analytical performance. Lactate biosensors show good reproducibility (RSD 4.9%, n = 10) and sensitivity (41,302 ± 546) μA/M cm 2 , with a good limit of detection (6.9 μM). Covalent immobilization of the enzyme allows the reuse of the biosensor for several measurements, converting them in a cheap alternative to the solid electrodes. The long-term stability of the biosensors was also evaluated. 90% of the signal was kept after 3 months of storage at room temperature (RT), while 95% was retained after 18 months at − 20°C. These results demonstrate that the method provides sensitive electrochemical lactate biosensors where the stability of the enzymatic activity can be preserved for a long period of time in adequate storage conditions.

Research paper thumbnail of High oxygen reduction activity of few-walled carbon nanotubes with low nitrogen content

Applied Catalysis B: Environmental, 2014

Nitrogen-containing few-walled carbon nanotubes (N-FWCNTs) with very low nitrogen content (0.56 a... more Nitrogen-containing few-walled carbon nanotubes (N-FWCNTs) with very low nitrogen content (0.56 at.%) were obtained by a process involving the coating of acid functionalized FWCNTs with polyaniline (PANI) followed by pyrolysis at high temperatures. The resulting N-FWCNTs exhibited a remarkable electrocatalytic activity for the oxygen reduction reaction (ORR), despite significantly lower nitrogen content than previously reported in literature. The N-FWCNTs performed on par or better than Pt-C in the cathode of an alkaline direct methanol fuel cell, corroborating the ORR activity observed in the electrochemical cell and exhibiting a higher methanol tolerance. Interestingly, N-FWCNTs showed a high activity for the hydrogen evolution reaction and for the hydrogen peroxide decomposition, suggesting that the active sites involved in ORR can simultaneously catalyze other reactions. This unprecedentedly high activity for such a low N-content can be explained by the exceptional accessibility for the catalytic sites located in open and porous N-doped layer surrounding the FWCNT core, along with the minimization of inactive inner volume and mass compared to larger nitrogen doped multiwalled tubes.

Research paper thumbnail of Atomic Layer Deposition Preparation of Pd Nanoparticles on a Porous Carbon Support for Alcohol Oxidation

The Journal of Physical Chemistry C, 2011

Direct alcohol fuel cells (DAFCs) are promising energy sources for low-power demand devices such ... more Direct alcohol fuel cells (DAFCs) are promising energy sources for low-power demand devices such as laptops and mobile phones. However, the reaction rate of sluggish alcohol oxidation at the anode is still one of the key factors preventing their commercialization. The reaction rate can be enhanced in alkaline media, 2À5 and the interest in alkaline DAFCs has recently increased because of the development of anion exchange membranes. 6À9 For further enhancement, alcohol oxidation noble metals can be used as catalysts. In acidic media, platinum is most commonly applied as an electrocatalyst by itself or as an alloy; however, in alkaline media palladium has also shown high activity, especially for ethanol and isopropanol oxidation. These alcohols are interesting alternatives to the widely used methanol because of their lower crossover rate, 12,13 higher boiling points, lower toxicity, and high performance in preliminary fuel cell tests. Currently, most noble metal catalysts used in fuel cell applications are produced using a liquidÀsolid nanoparticle synthesis that results in inhomogeneous catalyst materials that affect dramatically the particle size distribution and electrochemically active surface area (EASA) of the catalyst. Because of the high cost and low availability of noble metals the loading on the catalyst must be decreased if DAFCs are to compete with other power sources in commercial applications.

Research paper thumbnail of Adsorption Behavior of Perfluorinated Sulfonic Acid Ionomer on Highly Graphitized Carbon Nanofibers and Their Thermal Stabilities

The Journal of Physical Chemistry C, 2014

A systematic adsorption study of perfluorinated sulfonic acid Nafion ionomer on ribbon-type highl... more A systematic adsorption study of perfluorinated sulfonic acid Nafion ionomer on ribbon-type highly graphitized carbon nanofibers (CNFs) was carried out using fluorine-19 nuclear magnetic resonance spectroscopy. On the basis of the values obtained for the equilibrium constant (K eq , derived from Langmuir isotherm), the ionomer has varying affinities for CNFs (K eq between 5 and 22) as compared to Vulcan (K eq = 18), depending on surface treatments. However, the interactions are most likely governed by different adsorption mechanisms depending on hydrophilicity/hydrophobicity of the adsorbent carbon. The ionomer is probably adsorbed via the polar sulfonic group on hydrophilic Vulcan, whereas it is adsorbed primarily via hydrophobic −CF 2 − backbone on the highly hydrophobic pristine CNFs. Ionomer adsorption behavior is gradually altered from apolar to polar group adsorption for the acidmodified CNFs of decreasing hydrophobicity. This is indicated by the initial decrease and then increase in the value of K eq with the increasing strength of the acid treatment. The corresponding carbon−ionomer composite also showed varying thermal stability depending on Nafion orientation. The specific maximum surface coverage (Γ Smax ) of the CNFs is 1 order of magnitude higher than that of Vulcan. The large discrepancy is due to the fact that the ionomers are inaccessible to the internal surface area of Vulcan with high microporosity.

Research paper thumbnail of Durability of carbon nanofiber (CNF) & carbon nanotube (CNT) as catalyst support for Proton Exchange Membrane Fuel Cells

Solid State Ionics, 2013

research. It gives fundamental definition for cell life time, capital cost, system stability and ... more research. It gives fundamental definition for cell life time, capital cost, system stability and technique reliability. Loss of catalyst surface area due to corrosion of supporting material (normally carbon black) is one of the essential degradation mechanisms during cell operation. In this work, durability of carbon nanofibers (CNF) & carbon nanotubes (CNT) as alternative platinum catalyst supports for Proton Exchange Membrane Fuel Cells (PEMFCs) was assessed. Platinized CNF and CNT using a standard polyol method were prepared and fabricated as cathodes of Membrane Electrode Assemblies (MEA) for PEMFC. Both the catalysts as such and the MEAs made out of them were evaluated regarding to thermal and electrochemical stabilities using traditional carbon black (Vulcan XC72) as a reference. Thermal gravimetric analysis (TGA), cyclic voltammetry (CV), polarization curve and impedance spectroscopy were applied on the samples under accelerated stress conditions. The carbon nano-materials demonstrated better stability as a support for nano-sized platinum catalyst under PEMFC related operating conditions. Due to different morphology of the nano carbons compared to Vulcan XC 72 the electrode structures may still need optimization to improve the overall cell performance.

Research paper thumbnail of Synthesis of carbon nanofibres over nanoporous Ni–MgO catalyst: influence of the bimetallic Ni–(Cu, Co, Mo) MgO catalysts

Journal of Experimental Nanoscience, 2012

Research paper thumbnail of Influence of different carbon nanostructures on the electrocatalytic activity and stability of Pt supported electrocatalysts

International Journal of Hydrogen Energy, 2014

Commercially available graphitized carbon nanofibers and multi-walled carbon nanotubes, two carbo... more Commercially available graphitized carbon nanofibers and multi-walled carbon nanotubes, two carbon materials with very different structure, have been functionalized in a nitric esulfuric acid mixture. Further on, the materials have been platinized by a microwave assisted polyol method. The relative degree of graphitization has been estimated by means of Raman spectroscopy and X-ray diffraction while the relative concentration of oxygen containing groups has been estimated by X-ray photoelectron spectroscopy, which resulted in a graphitic character trend: Pt/GNF > Pt/F-GNF \ Pt/MWCNT > Pt/F-MWCNT. Transmission electron microscopy showed that the Pt particle size is around 3 nm for all samples, which was similar to the crystallite size obtained by X-ray diffraction. The activity towards electrochemical reduction of oxygen has been quantified using the thin-film rotating disk electrode, which has shown that all the samples have a better activity than the commercially available electrocatalysts. The trend obtained for the graphitic character maintained for the electrochemical activity, while the reverse trend has been obtained for the accelerated ageing test. Long-term potential cycling has demonstrated that the functionalization improves the stability for multi-walled carbon nanotubes, at the cost of decreased activity.

Research paper thumbnail of Durability of different carbon nanomaterial supports with PtRu catalyst in a direct methanol fuel cell

International Journal of Hydrogen Energy, 2012

a b s t r a c t PtRu catalysts with similar particle size and composition were deposited on three... more a b s t r a c t PtRu catalysts with similar particle size and composition were deposited on three different carbon supports: Vulcan, graphitized carbon nanofibers (GNF) and few-walled carbon nanotubes (FWCNT) and their performance for methanol oxidation was studied in an electrochemical cell and in a single cell DMFC. The electrochemical results indicate that with PtRu/GNF and PtRu/FWCNT higher current densities are obtained and oxidation intermediates deactivate the surface less compared to the same catalyst on Vulcan support. Conversely, PtRu/Vulcan provided the highest open circuit voltage OCV and current densities in DMFC experiments due to a well-optimized electrode layer structure.

Research paper thumbnail of The effect of Nafion content in a graphitized carbon nanofiber-based anode for the direct methanol fuel cell

International Journal of Hydrogen Energy, 2012

Direct methanol fuel cell Carbon nanofiber Nafion Ionomer content Anode structure Durability a b ... more Direct methanol fuel cell Carbon nanofiber Nafion Ionomer content Anode structure Durability a b s t r a c t The performance and stability of a direct methanol fuel cell (DMFC) with membrane electrode assemblies (MEA) using different Nafion Ò contents (30, 50 and 70 wt% or MEA30, MEA50 and MEA70, respectively) and graphitized carbon nanofiber (GNF) supported PtRu catalyst at the anode was investigated by a constant current measurement of 9 days (230 h) in a DMFC and characterization with various techniques before and after this measurement. Of the pristine MEAs, MEA50 reached the highest power and current densities.

Research paper thumbnail of Kinetics of methane decomposition to COx-free hydrogen and carbon nanofiber over Ni–Cu/MgO catalyst

International Journal of Hydrogen Energy, 2010

Keywords: Kinetic modeling Methane decomposition CO-free hydrogen Carbon nanofibers a b s t r a c... more Keywords: Kinetic modeling Methane decomposition CO-free hydrogen Carbon nanofibers a b s t r a c t Kinetic modeling of methane decomposition to CO x -free hydrogen and carbon nanofiber has been carried out in the temperature range 550e650 C over NieCu/MgO catalyst from CH 4 eH 2 mixtures at atmospheric pressure. Assuming the different mechanisms of the reaction, several kinetic models were derived based on LangmuireHinshelwood type. The optimum value of kinetic parameters has been obtained by Genetic Algorithm and statistical analysis has been used for the model discrimination. The suggested kinetic model relates to the mechanism when the dissociative adsorption of methane molecule is the rate-determining stage and the estimated activation energy is 50.4 kJ/mol in agreement with the literature. The catalyst deactivation was found to be dependent on the time, reaction temperature, and partial pressures of methane and hydrogen. Inspection of the behavior of the catalyst activity in relation to time, led to a model of second order for catalyst deactivation. (R. Karimzadeh). A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / h e i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 0 ) 1 e1 0 Please cite this article in press as: Borghei M, et al., Kinetics of methane decomposition to CO x -free hydrogen and carbon nanofiber over NieCu

Research paper thumbnail of Enhanced performance of a silicon microfabricated direct methanol fuel cell with PtRu catalysts supported on few-walled carbon nanotubes

Energy, 2014

Si-MFCs (Silicon micro fuel cells) are promising power supplies for microelectronic applications,... more Si-MFCs (Silicon micro fuel cells) are promising power supplies for microelectronic applications, however their development is still at early stages compared to the conventional PEM-FCs (proton exchange membrane fuel cells). There are not many published reports on the durability of Si-MFCs and those available only projected the life-time of standard Vulcan based catalysts. However, the limited durability resulting from carbon corrosion is one of the crucial issues in fuel cells. In this study, Si-MFC with an integrated silicon nanograss diffusion layer is used for the direct methanol fuel cell investigations. The long-term (3-day) performance of PtRu catalysts supported on different carbon supports, namely Vulcan, GNFs (Graphitized carbon nanofibers) and FWCNTs (Few-walled carbon nanotubes), was studied. PtRu-FWCNTs and PtRu-GNFs exhibited respectively 471% (20.0 mW cm À2 ) and 274% (13.1 mW cm À2 ) power density enhancements compared to PtRu-Vulcan (3.5 mW cm À2 ). After 3-day durability measurements, power density stayed at 72%, 68% and 91% of the initial value, respectively for PtRu-FWCNTs, PtRu-GNFs and PtRu-Vulcan. To evaluate the influence of carbon supports as well as the distribution and the size of the nanoparticles on the overall performance of Si-MFCs, further characterizations with Raman, BET (BrunauereEmmetteTeller), XRD (X-ray diffraction), SEM (Scanning electron microscopy) and TEM (Transmission Electron microscopy) were performed.

Research paper thumbnail of Highly catalytic carbon nanotube counter electrode on plastic for dye solar cells utilizing cobalt-based redox mediator

Electrochimica Acta, 2013

ABSTRACT

Research paper thumbnail of High-concentration aqueous dispersions of graphene produced by exfoliation of graphite using cellulose nanocrystals

Carbon, 2014

Stable high-concentration aqueous dispersions (>1 mg ml À1 ) of single and few-layer graphene fla... more Stable high-concentration aqueous dispersions (>1 mg ml À1 ) of single and few-layer graphene flakes were produced by direct exfoliation of graphite using cellulose nanocrystals (CNC). Biodegradable and widely available from renewable sources, CNC have proven to be very efficient graphene stabilizers even at low concentrations (0.2 mg ml À1 ), thus enabling remarkably high graphene/CNC ratios (up to 3.8). address: vruiz@cidetec.es (V. Ruiz). C A R B O N 7 0 ( 2 0 1 4 ) 1 5 7 -1 6 3 A v ai l abl e a t w w w . s c i e n c e d i r e c t. c o m ScienceDirect j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c a r b o n

Research paper thumbnail of Disposable amperometric biosensor based on lactate oxidase immobilised on platinum nanoparticle-decorated carbon nanofiber and poly(diallyldimethylammonium chloride) films

Biosensors and Bioelectronics, 2014

A novel biosensor for lactate has been developed, using screen-printed carbon electrodes (SPCE) a... more A novel biosensor for lactate has been developed, using screen-printed carbon electrodes (SPCE) and lactate oxidase (LOx). The active surface of the electrodes was modified using a dispersion of platinum nanoparticle decorated carbon nanofibers (PtNp-CNF) in poly(diallyldimethylammonium) chloride (PDDA) solution. In this way, sensitive, disposable, low cost and reliable hydrogen peroxide sensors were obtained. The immobilisation of LOx on top of these PtNp-CNF-PDDA/SPCEs resulted in amperometric biosensors with high operational stability. The sensitivity of the optimised lactate biosensor was 36.8 (mA/M cm 2 ) with a linear range of 25-1500 mM. The limit of detection was 11 mM (S/N¼ 3). Reproducibility, selectivity and storage stability were also evaluated. Additionally, the stability of the biosensor was also predicted by a model based on thermal degradation. Finally, lactate in sweat and blood samples was determined in a sport test using LOx/PtNp-CNF-PDDA/SPCEs and commercial biosensors respectively. Based on these data, the validity of the sweat lactate for the determination of the lactate threshold is discussed.

Research paper thumbnail of Interaction of multi-walled carbon nanotubes with perfluorinated sulfonic acid ionomers and surface treatment studies

Carbon, 2014

The interaction between high surface area nano-carbon catalyst supports for proton exchange membr... more The interaction between high surface area nano-carbon catalyst supports for proton exchange membrane fuel cells (PEMFCs) and perfluorinated sulfonic acid (Nafion â ) ionomer was studied 19 fluorine nuclear magnetic resonance spectroscopy ( 19 F-NMR). The method was developed and improved for more efficient, user-friendly and systematic studies based on our earlier experience. In this work, multi-walled carbon nanotubes (MWCNTs) from Showa Denko â and the corresponding acid modified products were explored. The adsorption at low concentration was found to follow a Langmuir isotherm.

Research paper thumbnail of CO-free Hydrogen production via Decomposition of Methane over Co-Mo-MgO Catalysis

Conventional processes for the production of hydrogen such as partial oxidation or steam reformin... more Conventional processes for the production of hydrogen such as partial oxidation or steam reforming of natural gas are multi-stage and complex which emit large amounts of CO 2 . Thermocatalytic decomposition (TCD) of methane is a potential route to production of CO-free hydrogen which can be directly entered to the fuel cells. The valuable by-product, pure carbon, is also formed which can extremely reduce the net cost of the process. In this work the TCD of methane over the Co-Mo-MgO catalyst at 900˚C was carried out in a fixed bed reactor and the exit gas of the reactor was analyzed by GC. The conversion of methane decomposition showed high value at the beginning. However, it gradually decreased with the time on stream. It is due to the formation of encapsulating carbon on the active metal sites which deactivates the catalyst during the time. The detailed description of the metal-catalyzed methane decomposition mechanism has been discussed in this paper.

Research paper thumbnail of Flexible metal-free counter electrode for dye solar cells based on conductive polymer and carbon nanotubes

Journal of electroanalytical chemistry

The counter electrodes (CEs) for flexible dye solar cells (DSCs) are normally prepared by sputter... more The counter electrodes (CEs) for flexible dye solar cells (DSCs) are normally prepared by sputtering platinum on indium tin oxide (ITO) plastic substrate. However both ITO and platinum are expensive materials that need to be replaced with cheaper alternatives in large scale production of low-cost DSCs. We fabricated a flexible and completely carbon-based CE for DSCs based on electropolymerized poly (3,4-ethylenedioxythiophene) (PEDOT) on single-walled carbon nanotube (SWCNT) film on a plain plastic substrate. The DSCs with such a CE had an efficiency of 4.0%, which is similar to the efficiency of the reference DSCs (3.9%) based on conventional sputtered platinum on ITO-plastic CE. The carbon-based electrode was prepared by a simple press-transfer method of SWCNTs from the collection filter used in the gas phase synthesis and by electrochemical deposition of PEDOT on it. Electrochemical impedance spectroscopy confirmed that the PEDOT–SWCNT film had the best catalytic performance amon...

Research paper thumbnail of Highly efficient cathode catalyst layer based on nitrogen-doped carbon nanotubes for the alkaline direct methanol fuel cell

Applied Catalysis B: Environmental, 2014

The performance of a direct methanol alkaline anion-exchange membrane (Fumatech FAA3) fuel cell w... more The performance of a direct methanol alkaline anion-exchange membrane (Fumatech FAA3) fuel cell with Pt-free nitrogen-doped few-walled carbon nanotubes (N-FWCNT) as the cathode catalyst is compared with a commercial supported Pt catalyst. The ionomer content of the N-FWCNT cathode catalyst layer is therefore optimized and it is shown to be 40 wt% of FAA3. Scanning electron microscopy images of the catalyst layer show that the ionomer forms aggregates with N-FWCNTs probably due to their charged nature and that the catalyst layer structure is remarkably open even with high ionomer contents facilitating the mass transfer of reactants and products to the active sites. With oxygen as the oxidant, the maximum power density obtained with our Pt-free N-FWCNTs (0.78 mW cm −2 ) is slightly higher than with the Pt catalyst (0.72 mW cm −2 ). However, when more practical air is used as the oxidant, the N-FWCNTs (0.73 mW cm −2 ) show clearly superior performance compared to the Pt catalyst (0.18 mW cm −2 ). The lower performance with the Pt catalyst is attributed to the denser electrode layer structure resulting in higher mass transport resistance and to the presence of methanol in the cathode, which poisons the Pt but not the N-FWCNTs.

Research paper thumbnail of Activity and stability studies of platinized multi-walled carbon nanotubes as fuel cell electrocatalysts

Applied Catalysis B: Environmental, 2015

Research paper thumbnail of Nitrogen-doped graphene with enhanced oxygen reduction activity produced by pyrolysis of graphene functionalized with imidazole derivatives

International Journal of Hydrogen Energy, 2014

Electrocatalyst Oxygen reduction reaction a b s t r a c t Nitrogen-doped graphene nanoplatelets (... more Electrocatalyst Oxygen reduction reaction a b s t r a c t Nitrogen-doped graphene nanoplatelets (N-GNP) with 1.6e3.3 at.% nitrogen content were synthesized by thermal annealing of GNP functionalized with a series of imidazole-based nitrogen-containing precursors of different nature, charge and nitrogen content. The imidazole derivatives included one ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4) and two polymers, a neutral one, poly(vinylimidazole) (PVI) and a poly(ionic liquid), poly(3-butyl-1-vinylimidazolium bromide) (PBVIBr). N-GNP showed enhanced electrocatalytic activity for oxygen reduction reaction (ORR) in alkaline media compared to pristine GNP, with the number of electrons transferred in oxygen-saturated KOH at low overpotentials following the trend: 2.5 (pristine GNP) < 2.9 (N-GNP from PVI eGNP) < 3.3 (N-GNP from BMIBF 4 eGNP) < 3.5 (N-GNP from PBVIBr-GNP). Interestingly, ORR catalytic activity did not correlate with total nitrogen content but was more affected by BrunauereEmmetteTeller (BET) surface area. The most active materials were N-GNP with lowest doping levels and highest surface area resulting from the ionic (imidazolium-based) nitrogen precursors.

Research paper thumbnail of Graphitized carbon nanofiber–Pt nanoparticle hybrids as sensitive tool for preparation of screen printing biosensors. Detection of lactate in wines and ciders

Bioelectrochemistry, 2015

This work describes the fabrication of a new lactate biosensor. The strategy is based on the use ... more This work describes the fabrication of a new lactate biosensor. The strategy is based on the use of a novel hybrid nanomaterial for amperometric biosensors i.e. platinum nanoparticles (PtNps) supported on graphitized carbon nanofibers (PtNps/GCNF) prepared by chemical reduction of the Pt precursor at GCNF surfaces. The biosensors were constructed by covalent immobilization of lactate oxidase (LOx) onto screen printed carbon electrodes (SPCEs) modified with PtNps (PtNps/GCNF-SPCEs) using polyethyleneimine (PEI) and glutaraldehyde (GA). Experimental variables concerning both the biosensor design and the detection process were investigated for an optimal analytical performance. Lactate biosensors show good reproducibility (RSD 4.9%, n = 10) and sensitivity (41,302 ± 546) μA/M cm 2 , with a good limit of detection (6.9 μM). Covalent immobilization of the enzyme allows the reuse of the biosensor for several measurements, converting them in a cheap alternative to the solid electrodes. The long-term stability of the biosensors was also evaluated. 90% of the signal was kept after 3 months of storage at room temperature (RT), while 95% was retained after 18 months at − 20°C. These results demonstrate that the method provides sensitive electrochemical lactate biosensors where the stability of the enzymatic activity can be preserved for a long period of time in adequate storage conditions.

Research paper thumbnail of High oxygen reduction activity of few-walled carbon nanotubes with low nitrogen content

Applied Catalysis B: Environmental, 2014

Nitrogen-containing few-walled carbon nanotubes (N-FWCNTs) with very low nitrogen content (0.56 a... more Nitrogen-containing few-walled carbon nanotubes (N-FWCNTs) with very low nitrogen content (0.56 at.%) were obtained by a process involving the coating of acid functionalized FWCNTs with polyaniline (PANI) followed by pyrolysis at high temperatures. The resulting N-FWCNTs exhibited a remarkable electrocatalytic activity for the oxygen reduction reaction (ORR), despite significantly lower nitrogen content than previously reported in literature. The N-FWCNTs performed on par or better than Pt-C in the cathode of an alkaline direct methanol fuel cell, corroborating the ORR activity observed in the electrochemical cell and exhibiting a higher methanol tolerance. Interestingly, N-FWCNTs showed a high activity for the hydrogen evolution reaction and for the hydrogen peroxide decomposition, suggesting that the active sites involved in ORR can simultaneously catalyze other reactions. This unprecedentedly high activity for such a low N-content can be explained by the exceptional accessibility for the catalytic sites located in open and porous N-doped layer surrounding the FWCNT core, along with the minimization of inactive inner volume and mass compared to larger nitrogen doped multiwalled tubes.

Research paper thumbnail of Atomic Layer Deposition Preparation of Pd Nanoparticles on a Porous Carbon Support for Alcohol Oxidation

The Journal of Physical Chemistry C, 2011

Direct alcohol fuel cells (DAFCs) are promising energy sources for low-power demand devices such ... more Direct alcohol fuel cells (DAFCs) are promising energy sources for low-power demand devices such as laptops and mobile phones. However, the reaction rate of sluggish alcohol oxidation at the anode is still one of the key factors preventing their commercialization. The reaction rate can be enhanced in alkaline media, 2À5 and the interest in alkaline DAFCs has recently increased because of the development of anion exchange membranes. 6À9 For further enhancement, alcohol oxidation noble metals can be used as catalysts. In acidic media, platinum is most commonly applied as an electrocatalyst by itself or as an alloy; however, in alkaline media palladium has also shown high activity, especially for ethanol and isopropanol oxidation. These alcohols are interesting alternatives to the widely used methanol because of their lower crossover rate, 12,13 higher boiling points, lower toxicity, and high performance in preliminary fuel cell tests. Currently, most noble metal catalysts used in fuel cell applications are produced using a liquidÀsolid nanoparticle synthesis that results in inhomogeneous catalyst materials that affect dramatically the particle size distribution and electrochemically active surface area (EASA) of the catalyst. Because of the high cost and low availability of noble metals the loading on the catalyst must be decreased if DAFCs are to compete with other power sources in commercial applications.

Research paper thumbnail of Adsorption Behavior of Perfluorinated Sulfonic Acid Ionomer on Highly Graphitized Carbon Nanofibers and Their Thermal Stabilities

The Journal of Physical Chemistry C, 2014

A systematic adsorption study of perfluorinated sulfonic acid Nafion ionomer on ribbon-type highl... more A systematic adsorption study of perfluorinated sulfonic acid Nafion ionomer on ribbon-type highly graphitized carbon nanofibers (CNFs) was carried out using fluorine-19 nuclear magnetic resonance spectroscopy. On the basis of the values obtained for the equilibrium constant (K eq , derived from Langmuir isotherm), the ionomer has varying affinities for CNFs (K eq between 5 and 22) as compared to Vulcan (K eq = 18), depending on surface treatments. However, the interactions are most likely governed by different adsorption mechanisms depending on hydrophilicity/hydrophobicity of the adsorbent carbon. The ionomer is probably adsorbed via the polar sulfonic group on hydrophilic Vulcan, whereas it is adsorbed primarily via hydrophobic −CF 2 − backbone on the highly hydrophobic pristine CNFs. Ionomer adsorption behavior is gradually altered from apolar to polar group adsorption for the acidmodified CNFs of decreasing hydrophobicity. This is indicated by the initial decrease and then increase in the value of K eq with the increasing strength of the acid treatment. The corresponding carbon−ionomer composite also showed varying thermal stability depending on Nafion orientation. The specific maximum surface coverage (Γ Smax ) of the CNFs is 1 order of magnitude higher than that of Vulcan. The large discrepancy is due to the fact that the ionomers are inaccessible to the internal surface area of Vulcan with high microporosity.

Research paper thumbnail of Durability of carbon nanofiber (CNF) & carbon nanotube (CNT) as catalyst support for Proton Exchange Membrane Fuel Cells

Solid State Ionics, 2013

research. It gives fundamental definition for cell life time, capital cost, system stability and ... more research. It gives fundamental definition for cell life time, capital cost, system stability and technique reliability. Loss of catalyst surface area due to corrosion of supporting material (normally carbon black) is one of the essential degradation mechanisms during cell operation. In this work, durability of carbon nanofibers (CNF) & carbon nanotubes (CNT) as alternative platinum catalyst supports for Proton Exchange Membrane Fuel Cells (PEMFCs) was assessed. Platinized CNF and CNT using a standard polyol method were prepared and fabricated as cathodes of Membrane Electrode Assemblies (MEA) for PEMFC. Both the catalysts as such and the MEAs made out of them were evaluated regarding to thermal and electrochemical stabilities using traditional carbon black (Vulcan XC72) as a reference. Thermal gravimetric analysis (TGA), cyclic voltammetry (CV), polarization curve and impedance spectroscopy were applied on the samples under accelerated stress conditions. The carbon nano-materials demonstrated better stability as a support for nano-sized platinum catalyst under PEMFC related operating conditions. Due to different morphology of the nano carbons compared to Vulcan XC 72 the electrode structures may still need optimization to improve the overall cell performance.

Research paper thumbnail of Synthesis of carbon nanofibres over nanoporous Ni–MgO catalyst: influence of the bimetallic Ni–(Cu, Co, Mo) MgO catalysts

Journal of Experimental Nanoscience, 2012

Research paper thumbnail of Influence of different carbon nanostructures on the electrocatalytic activity and stability of Pt supported electrocatalysts

International Journal of Hydrogen Energy, 2014

Commercially available graphitized carbon nanofibers and multi-walled carbon nanotubes, two carbo... more Commercially available graphitized carbon nanofibers and multi-walled carbon nanotubes, two carbon materials with very different structure, have been functionalized in a nitric esulfuric acid mixture. Further on, the materials have been platinized by a microwave assisted polyol method. The relative degree of graphitization has been estimated by means of Raman spectroscopy and X-ray diffraction while the relative concentration of oxygen containing groups has been estimated by X-ray photoelectron spectroscopy, which resulted in a graphitic character trend: Pt/GNF > Pt/F-GNF \ Pt/MWCNT > Pt/F-MWCNT. Transmission electron microscopy showed that the Pt particle size is around 3 nm for all samples, which was similar to the crystallite size obtained by X-ray diffraction. The activity towards electrochemical reduction of oxygen has been quantified using the thin-film rotating disk electrode, which has shown that all the samples have a better activity than the commercially available electrocatalysts. The trend obtained for the graphitic character maintained for the electrochemical activity, while the reverse trend has been obtained for the accelerated ageing test. Long-term potential cycling has demonstrated that the functionalization improves the stability for multi-walled carbon nanotubes, at the cost of decreased activity.

Research paper thumbnail of Durability of different carbon nanomaterial supports with PtRu catalyst in a direct methanol fuel cell

International Journal of Hydrogen Energy, 2012

a b s t r a c t PtRu catalysts with similar particle size and composition were deposited on three... more a b s t r a c t PtRu catalysts with similar particle size and composition were deposited on three different carbon supports: Vulcan, graphitized carbon nanofibers (GNF) and few-walled carbon nanotubes (FWCNT) and their performance for methanol oxidation was studied in an electrochemical cell and in a single cell DMFC. The electrochemical results indicate that with PtRu/GNF and PtRu/FWCNT higher current densities are obtained and oxidation intermediates deactivate the surface less compared to the same catalyst on Vulcan support. Conversely, PtRu/Vulcan provided the highest open circuit voltage OCV and current densities in DMFC experiments due to a well-optimized electrode layer structure.

Research paper thumbnail of The effect of Nafion content in a graphitized carbon nanofiber-based anode for the direct methanol fuel cell

International Journal of Hydrogen Energy, 2012

Direct methanol fuel cell Carbon nanofiber Nafion Ionomer content Anode structure Durability a b ... more Direct methanol fuel cell Carbon nanofiber Nafion Ionomer content Anode structure Durability a b s t r a c t The performance and stability of a direct methanol fuel cell (DMFC) with membrane electrode assemblies (MEA) using different Nafion Ò contents (30, 50 and 70 wt% or MEA30, MEA50 and MEA70, respectively) and graphitized carbon nanofiber (GNF) supported PtRu catalyst at the anode was investigated by a constant current measurement of 9 days (230 h) in a DMFC and characterization with various techniques before and after this measurement. Of the pristine MEAs, MEA50 reached the highest power and current densities.

Research paper thumbnail of Kinetics of methane decomposition to COx-free hydrogen and carbon nanofiber over Ni–Cu/MgO catalyst

International Journal of Hydrogen Energy, 2010

Keywords: Kinetic modeling Methane decomposition CO-free hydrogen Carbon nanofibers a b s t r a c... more Keywords: Kinetic modeling Methane decomposition CO-free hydrogen Carbon nanofibers a b s t r a c t Kinetic modeling of methane decomposition to CO x -free hydrogen and carbon nanofiber has been carried out in the temperature range 550e650 C over NieCu/MgO catalyst from CH 4 eH 2 mixtures at atmospheric pressure. Assuming the different mechanisms of the reaction, several kinetic models were derived based on LangmuireHinshelwood type. The optimum value of kinetic parameters has been obtained by Genetic Algorithm and statistical analysis has been used for the model discrimination. The suggested kinetic model relates to the mechanism when the dissociative adsorption of methane molecule is the rate-determining stage and the estimated activation energy is 50.4 kJ/mol in agreement with the literature. The catalyst deactivation was found to be dependent on the time, reaction temperature, and partial pressures of methane and hydrogen. Inspection of the behavior of the catalyst activity in relation to time, led to a model of second order for catalyst deactivation. (R. Karimzadeh). A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / h e i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 0 ) 1 e1 0 Please cite this article in press as: Borghei M, et al., Kinetics of methane decomposition to CO x -free hydrogen and carbon nanofiber over NieCu

Research paper thumbnail of Enhanced performance of a silicon microfabricated direct methanol fuel cell with PtRu catalysts supported on few-walled carbon nanotubes

Energy, 2014

Si-MFCs (Silicon micro fuel cells) are promising power supplies for microelectronic applications,... more Si-MFCs (Silicon micro fuel cells) are promising power supplies for microelectronic applications, however their development is still at early stages compared to the conventional PEM-FCs (proton exchange membrane fuel cells). There are not many published reports on the durability of Si-MFCs and those available only projected the life-time of standard Vulcan based catalysts. However, the limited durability resulting from carbon corrosion is one of the crucial issues in fuel cells. In this study, Si-MFC with an integrated silicon nanograss diffusion layer is used for the direct methanol fuel cell investigations. The long-term (3-day) performance of PtRu catalysts supported on different carbon supports, namely Vulcan, GNFs (Graphitized carbon nanofibers) and FWCNTs (Few-walled carbon nanotubes), was studied. PtRu-FWCNTs and PtRu-GNFs exhibited respectively 471% (20.0 mW cm À2 ) and 274% (13.1 mW cm À2 ) power density enhancements compared to PtRu-Vulcan (3.5 mW cm À2 ). After 3-day durability measurements, power density stayed at 72%, 68% and 91% of the initial value, respectively for PtRu-FWCNTs, PtRu-GNFs and PtRu-Vulcan. To evaluate the influence of carbon supports as well as the distribution and the size of the nanoparticles on the overall performance of Si-MFCs, further characterizations with Raman, BET (BrunauereEmmetteTeller), XRD (X-ray diffraction), SEM (Scanning electron microscopy) and TEM (Transmission Electron microscopy) were performed.

Research paper thumbnail of Highly catalytic carbon nanotube counter electrode on plastic for dye solar cells utilizing cobalt-based redox mediator

Electrochimica Acta, 2013

ABSTRACT

Research paper thumbnail of High-concentration aqueous dispersions of graphene produced by exfoliation of graphite using cellulose nanocrystals

Carbon, 2014

Stable high-concentration aqueous dispersions (>1 mg ml À1 ) of single and few-layer graphene fla... more Stable high-concentration aqueous dispersions (>1 mg ml À1 ) of single and few-layer graphene flakes were produced by direct exfoliation of graphite using cellulose nanocrystals (CNC). Biodegradable and widely available from renewable sources, CNC have proven to be very efficient graphene stabilizers even at low concentrations (0.2 mg ml À1 ), thus enabling remarkably high graphene/CNC ratios (up to 3.8). address: vruiz@cidetec.es (V. Ruiz). C A R B O N 7 0 ( 2 0 1 4 ) 1 5 7 -1 6 3 A v ai l abl e a t w w w . s c i e n c e d i r e c t. c o m ScienceDirect j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c a r b o n

Research paper thumbnail of Disposable amperometric biosensor based on lactate oxidase immobilised on platinum nanoparticle-decorated carbon nanofiber and poly(diallyldimethylammonium chloride) films

Biosensors and Bioelectronics, 2014

A novel biosensor for lactate has been developed, using screen-printed carbon electrodes (SPCE) a... more A novel biosensor for lactate has been developed, using screen-printed carbon electrodes (SPCE) and lactate oxidase (LOx). The active surface of the electrodes was modified using a dispersion of platinum nanoparticle decorated carbon nanofibers (PtNp-CNF) in poly(diallyldimethylammonium) chloride (PDDA) solution. In this way, sensitive, disposable, low cost and reliable hydrogen peroxide sensors were obtained. The immobilisation of LOx on top of these PtNp-CNF-PDDA/SPCEs resulted in amperometric biosensors with high operational stability. The sensitivity of the optimised lactate biosensor was 36.8 (mA/M cm 2 ) with a linear range of 25-1500 mM. The limit of detection was 11 mM (S/N¼ 3). Reproducibility, selectivity and storage stability were also evaluated. Additionally, the stability of the biosensor was also predicted by a model based on thermal degradation. Finally, lactate in sweat and blood samples was determined in a sport test using LOx/PtNp-CNF-PDDA/SPCEs and commercial biosensors respectively. Based on these data, the validity of the sweat lactate for the determination of the lactate threshold is discussed.

Research paper thumbnail of Interaction of multi-walled carbon nanotubes with perfluorinated sulfonic acid ionomers and surface treatment studies

Carbon, 2014

The interaction between high surface area nano-carbon catalyst supports for proton exchange membr... more The interaction between high surface area nano-carbon catalyst supports for proton exchange membrane fuel cells (PEMFCs) and perfluorinated sulfonic acid (Nafion â ) ionomer was studied 19 fluorine nuclear magnetic resonance spectroscopy ( 19 F-NMR). The method was developed and improved for more efficient, user-friendly and systematic studies based on our earlier experience. In this work, multi-walled carbon nanotubes (MWCNTs) from Showa Denko â and the corresponding acid modified products were explored. The adsorption at low concentration was found to follow a Langmuir isotherm.