Showing papers on "Direct methanol fuel cell published in 2004"

Carbon-Supported Pt and PtRu Nanoparticles as Catalysts for a Direct Methanol Fuel Cell

Abstract: Nanosized Pt and PtRu colloids were prepared by a microwave-assisted polyol process and transferred to a toluene solution of decanthiol Vulcan XC-72 was then added to the toluene solution to adsorb the thiolated Pt and PtRu colloids TEM examinations showed nearly spherical particles and narrow size distributions for both supported and unsupported metals The carbon-supported Pt and PtRu nanoparticles were activated by thermal treatment to remove the thiol stabilizing shell All Pt and PtRu catalysts (except Pt23Ru77) showed the X-ray diffraction pattern of a face-centered cubic (fcc) crystal structure, whereas the Pt23Ru77 alloy was more typical of the hexagonal close-packed (hcp) structure The electro-oxidation of liquid methanol on these catalysts was investigated at room temperature by cyclic voltammetry and chronoamperometry The results showed that the alloy catalyst was catalytically more active than pure platinum The heat-treated catalyst was also expectedly more active than the non-heat-treate

Physical and Electrochemical Characterizations of Microwave-Assisted Polyol Preparation of Carbon-Supported PtRu Nanoparticles

Abstract: PtRu nanoparticles supported on Vulcan XC-72 carbon and carbon nanotubes were prepared by a microwave-assisted polyol process. The catalysts were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). The PtRu nanoparticles, which were uniformly dispersed on carbon, were 2−6 nm in diameter. All PtRu/C catalysts prepared as such displayed the characteristic diffraction peaks of a Pt face-centered cubic structure, excepting that the 2θ values were shifted to slightly higher values. XPS analysis revealed that the catalysts contained mostly Pt(0) and Ru(0), with traces of Pt(II), Pt(IV), and Ru(IV). The electro-oxidation of methanol was studied by cyclic voltammetry, linear sweep voltammetry, and chronoamperometry. It was found that both PtRu/C catalysts had high and more durable electrocatalytic activities for methanol oxidation than a comparative Pt/C catalyst. Preliminary data from a direct methanol fuel cell single stack test cell using the Vulcan...

Ordered Porous Carbons with Tunable Pore Sizes as Catalyst Supports in Direct Methanol Fuel Cell

Abstract: Ordered uniform porous carbon frameworks with pore sizes in the range of 10 to ∼1000 nm were synthesized against removable colloidal silica crystalline templates by carbonization of phenol and formaldehyde as a carbon precursor. The porous carbons were used as supports for a Pt(50)−Ru(50) alloy catalyst to study their supporting effect on the anodic performance of the catalyst in a direct methanol fuel cell (DMFC). The use of the ordered uniform porous carbons resulted in much improved catalytic activity for methanol oxidation in the fuel cell probably due to their high surface areas, large pore volumes, and three-dimensionally interconnected uniform pore structures, which allow a higher degree of dispersion of the catalysts and efficient diffusion of reagents. In general, the smaller the pore sizes in the porous carbons were, the better the catalytic activity for methanol oxidation was. In addition, as pore sizes are getting smaller, the structural integrity with good pore interconnection seems to be get...

Ruthenium Crossover in Direct Methanol Fuel Cell with Pt-Ru Black Anode

Abstract: In this study, we provide electrochemical and X-ray fluorescence evidence of ruthenium crossover in direct methanol fuel cells using a state-of-the-art Pt-Ru alloy catalyst at the anode. We find ruthenium susceptible to leaching out from the highly active Pt-Ru black catalyst, crossing the proton-conducting Nafion membrane and redepositing at the Pt cathode on the opposite side of the fuel cell. After first detecting this phenomenon in a direct methanol fuel cell (DMFC) stack with a history of cell-voltage reversal, we have since observed ruthenium crossover under virtually all DMFC operating conditions, from single cell break-in (humidification) to stack life testing. The degree of cathode contamination by ruthenium species (of chemical form yet unknown) depends on, among other factors, the DMFC anode potential and the cell operating time. Once deposited at the cathode, ruthenium inhibits oxygen reduction kinetics and the catalyst's ability to handle methanol crossover. Depending on the degree of cathode contamination, the overall effect of ruthenium crossover on cell performance may be from as little as ∼40mV up to 200 mV.

Comparative Studies of Methanol Crossover and Cell Performance for a DMFC

Abstract: Fuel (methanol) crossover through the polymeric electrolyte membrane in a single direct methanol fuel cell (DMFC) was determined by monitoring the amount of CO 2 produced from methanol oxidation. Instead of measuring CO 2 from only the cathode by a conventional method, the amounts of CO 2 at both of the cathode and the anode were determined in the present study. Gravimetric determination of BaCO 3 was employed to accurately analyze the amount of CO 2 . The equivalent current of methanol crossover can be calculated from the discharge current of the fuel cell and the sum of dry BaCO 3 precipitate collected at the anode and the cathode exhausts. The common experimental deviation of measuring methanol crossover caused by CO 2 permeation through polymeric electrolyte membrane can be corrected with the proposed method. These data of methanol crossover were compared with the data of single cell polarization behaviors at different methanol concentrations and different temperatures. The energy density of the DMFC is not only dependent on the cell discharge performance but also significantly dependent on the faradaic efficiency that is directly linked to methanol crossover. Under the optimized operating conditions, 1.0 M methanol at 60°C, the DMFC has an energy density of 1800 Wh/kg based on pure methanol.

Studies on performance degradation of a direct methanol fuel cell (DMFC) in life test

Abstract: A 75 h life test of a direct methanol fuel cell (DMFC) at a low current density of 100 mA cm−2 was carried out. Electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied to characterize the membrane electrode assembly (MEA) during the life test. The EIS results showed that the high frequency cell impedance of the MEA increased from 0.26 ohm cm2 at the beginning of the life test to 0.37 ohm cm2 at the end. SEM images of the MEA in cross-section apparently demonstrated the delamination of the electrodes from the membrane after the life test. TEM analysis of the electrocatalysts in the pre- and post-test cell revealed that the agglomeration of the metal particles in the anode was more serious than in the cathode. The results indicate that the agglomeration of electrocatalysts together with the delamination of the MEA concurrently contribute to the performance degradation of the DMFC.

Direct Methanol Fuel Cell Performance of Disulfonated Poly(arylene ether benzonitrile) Copolymers

Abstract: This paper reports the performance of direct methanol fuel cells (DMFCs) using novel disulfonated poly(arylene ether benzonitrile) copolymers derived from hexafluoro-isopropylidene diphenol (6F), 2,6-dichlorobenzonitrile, and 3,3'-disulfonated 4,4'-dichloro diphenyl sulfone (SDCDPS). The membrane electrode assembly (MEA) which employed the sulfonated copolymer with 35 mol % of disulfonated comonomer as the proton exchange membrane had approximately 2-fold lower methanol crossover and slightly higher (about 10%) cell resistance than the MEA using the perfluorosulfonic acid Nafion membrane, resulting in an approximately 50% improvement in selectivity, regardless of membrane thickness. Accordingly, this MEA outperformed the Nafion MEA control in a DMFC single-cell test. For example, 200 mA/cm 2 was obtained (compared with 150 mA/cm 2 for the Nafion MEA) at 0.5 V at a temperature of 80°C and ambient air pressure. Similar experiments performed with nonfluorine-containing biphenol-based sulfonated poly(arylene ether sulfone) copolymers (BPSH) indicated that the compatibility of the polymer electrolyte with the electrodes likely has a critical role in initial DMFC performance.

A Review of Mathematical Models for Hydrogen and Direct Methanol Polymer Electrolyte Membrane Fuel Cells

Abstract: This paper presents a review of the mathematical modeling of two types of polymer electrolyte membrane fuel cells: hydrogen fuel cells and direct methanol fuel cells. Models of single cells are described as well as models of entire fuel cell stacks. Methods for obtaining model parameters are briefly summarized, as well as the numerical techniques used to solve the model equations. Effective models have been developed to describe the fundamental electrochemical and transport phenomena occurring in the diffusion layers, catalyst layers, and membrane. More research is required to develop models that are validated using experimental data, and models that can account for complex two-phase flows of liquids and gases.

Mathematical Model of a Direct Methanol Fuel Cell

Abstract: : A one dimensional (1-D), isothermal model for a direct methanol fuel cell (DMFC) is presented. This model accounts for the kinetics of the multi-step methanol oxidation reaction at the anode. Diffusion and crossover of methanol are modeled and the mixed potential of the oxygen cathode due to methanol crossover is included. Kinetic and diffusional parameters are estimated by comparing the model to data from a 25 cm2 DMFC. This semi-analytical model can be solved rapidly so that it is suitable for inclusion in real-time system level DMFC simulations.

Preparation of Pt–Ru bimetallic anodes by galvanostatic pulse electrodeposition: characterization and application to the direct methanol fuel cell

Abstract: The electrodeposition of platinum and ruthenium was carried out on carbon electrodes to prepare methanol anodes with different Pt/Ru atomic ratios using a galvanostatic pulse technique. Characterizations by XRD, TEM, EDX and atomic absorption spectroscopy indicated that most of the electrocatalytic anodes consisted of 2 mg cm−2 of Pt–Ru alloy particles with the desired composition and with particle sizes ranging from 5 to 8 nm. Electrochemical tests in a single DMFC show that these electrodes are very active for methanol oxidation and that the best Pt/Ru atomic ratio in the temperature range used (50–110 °C) is 80:20. The influence of the relaxation time t off was also studied and it appeared that a low t off led to smaller particle sizes and higher performances in terms of current density and power density.