Showing papers on "Direct methanol fuel cell published in 1999"

Role of hydrous ruthenium oxide in Pt-Ru direct methanol fuel cell anode electrocatalysts: The importance of mixed electron/proton conductivity

Abstract: Pt−Ru is the favored anode catalyst for the oxidation of methanol in direct methanol fuel cells (DMFCs). The nanoscale Pt−Ru blacks are accepted to be bimetallic alloys as based on their X-ray diffraction patterns. Our bulk and surface analyses show that although practical Pt−Ru blacks have diffraction patterns consistent with an alloy assignment, they are primarily a mix of Pt metal and Ru oxides plus some Pt oxides and only small amounts of Ru metal. Thermogravimetric analysis and X-ray photoelectron spectroscopy of as-received Pt−Ru electrocatalysts indicate that DMFC materials contain substantial amounts of hydrous ruthenium oxide (RuOxHy). A potential misidentification of nanoscale Pt−Ru blacks arises because RuOxHy is amorphous and cannot be discerned by X-ray diffraction. Hydrous ruthenium oxide is a mixed proton and electron conductor and innately expresses Ru−OH speciation. These properties are of key importance in the mechanism of methanol oxidation, in particular, Ru−OH is a critical component ...

Influence of Ionomer Content in Catalyst Layers on Direct Methanol Fuel Cell Performance

Abstract: The ionomer content in catalyst layers has a marked influence on direct methanol fuel cell (DMFC) performance. In an anode which contains unsupported PtRu as the catalyst, the recast ionomer may not always be necessary because the protonic conductivity of hydrous RuOx, the presence of which is inferred from the X‐ray diffraction pattern, may be sufficient to allow effective utilization of catalyst sites. To examine interpenetration of catalyst and membrane material as a possible explanation for the lack of an apparent need of added ionomer, ultramicrotomed thin sections of the membrane‐electrode assembly (MEA) were examined by scanning electron microscopy. Microscopic examination of such MEA cross sections revealed significant porosity in layers made by mixing unsupported catalysts with recast ionomer. Images of such sections did not reveal significant interpenetration, supporting the interpretation that hydrous RuOx may by itself provide sufficient protonic conductivity in PtRu catalyst layers prepared with no added ionomer. In contrast we show that the presence of recast ionomer in DMFC cathodes based on unsupported Pt as the catalyst is essential for optimum DMFC performance, because the recast ionomer is the primary source of protonic conductivity in the latter case. Having shown its potential function as proton conductor, we stress that Ru oxide is apparently not the key for maximizing DMFC anodic activity. © 1999 The Electrochemical Society. All rights reserved.

Gas evolution and power performance in direct methanol fuel cells

Abstract: The use of acrylic cells and a CCTV camera for visually investigating the carbon dioxide gas evolution process inside an operating direct methanol fuel cell environment is demonstrated. Also, the effect of operating parameters on the system gas management, using a series of tests with different gas diffusion layer supporting materials, flow bed designs, cell sizes and exhaust manifold configurations, is studied. Carbon dioxide gas management is an important issue obstructing progress in viable direct methanol fuel cell systems development. Gas evolution mechanisms and gas management techniques are discussed and analysed with reference to several video picture and performance data. The data demonstrate that Toray carbon paper is not a suitable material for DMFCs due to its poor gas removal properties. ‘A’ type carbon cloth shows relatively good gas removal behaviour. Increasing the liquid phase inlet flow rate is beneficial for gas removal. Increasing the current density results in higher gas production and in the formation of gas slugs, especially at low flow rates, which can lead to blocking of the channels and hence deterioration in the cell performance. A new flow bed design, based on a heat exchanger concept, is affective for gas management and gives a more uniform flow distribution in the flow bed channels. Using the results of this study, and the modelling techniques developed by our group, will are able to determine suitable operating conditions for our prototype 0.5 kW cell DMFC stack.

Performance of Direct Methanol Fuel Cells with Sputter‐Deposited Anode Catalyst Layers

Abstract: Performance of direct methanol fuel cells with sputter‐deposited anodes was investigated. The thin film catalyst layers were characterized using X‐ray diffraction, energy dispersive X‐ray analysis, Rutherford backscattering spectroscopy, and X‐ray photoelectron spectroscopy. Different catalyst loadings and membrane electrode assembly (MEA) fabrication processes were tested. The maximum power density achieved at was , and almost was attained with a loading of only . The results demonstrate that a catalyst utilization of at least can be achieved at current densities ranging from 260 to . The application of the sputter‐deposition method for MEA fabrication is particularly attractive for commercialization of direct methanol fuel cell technology. ©2000 The Electrochemical Society

A Direct Methanol Fuel Cell Based on a Novel Low‐Cost Nanoporous Proton‐Conducting Membrane

Abstract: We report here a low‐cost and improved direct methanol fuel cell (DMFC), based on a novel nanoporous proton‐conducting membrane (NP-PCM). The use of the NP-PCM in DMFC offers several advantages over the Nafion‐based DMFC; lower membrane cost (by more than two orders of magnitude), smaller pores (by a factor of two), and lower methanol crossover (by up to an order of magnitude), which lead to much higher fuel utilization. The NP‐PCM also has higher conductivity (by up to four times). In addition, the ionic conductivity of the NP‐PCM, unlike Nafion, is not affected by heavy metal impurities, thus it may permit the use of cheaper catalysts and hardware materials. The maximum power density achieved so far, at and at ambient oxygen pressure, is . ©2000 The Electrochemical Society

Enhanced methanol utilization in direct methanol fuel cell

Abstract: The fuel utilization of a direct methanol fuel cell is enhanced for improved cell efficiency Distribution plates at the anode and cathode of the fuel cell are configured to distribute reactants vertically and laterally uniformly over a catalyzed membrane surface of the fuel cell A conductive sheet between the anode distribution plate and the anodic membrane surface forms a mass transport barrier to the methanol fuel that is large relative to a mass transport barrier for a gaseous hydrogen fuel cell In a preferred embodiment, the distribution plate is a perforated corrugated sheet The mass transport barrier may be conveniently increased by increasing the thickness of an anode conductive sheet adjacent the membrane surface of the fuel cell

Design and Operation of an Electrochemical Methanol Concentration Sensor for Direct Methanol Fuel Cell Systems

Abstract: The development of a 150-Watt packaged power source based on liquid feed direct methanol fuel cells is being pursued currently at the Jet propulsion Laboratory for defense applications. In our studies we find that the concentration of methanol in the fuel circulation loop affects the electrical performance and efficiency the direct methanol fuel cell systems significantly. The practical operation of direct methanol fuel cell systems, therefore, requires accurate monitoring and control of methanol concentration. The present paper reports on the principle and demonstration of an in-house developed electrochemical sensor suitable for direct methanol fuel cell systems.

A 5 W liquid-feed solid-polymer-electrolyte direct methanol fuel cell stack with stainless steel

Abstract: The use of stainless steel as replacement for graphite in polymer-electrolyte-membrane fuel cells (PEMFCs) has been reported [1], with little difference in performance and corrosion of stainless steel even after prolonged testing of the PEMFC stacks. Therefore, for stationary applications where stack weight is not as critical as for transportation, the ruggedness of stainless steel, as well as its low-cost relative to graphite, make it an attractive material for practical use. To our knowledge, similar studies on solid polymer electrolyte direct methanol fuel cell (SPE-DMFC) stacks with stainless steel flow-dis-tributors are lacking in the literature. As a part of our ongoing research [2, 3] on direct methanol fuel cells, this communication reports the performance of a 5W liquid-feed stainless steel SPE-DMFC.

Recent advances in direct methanol fuel cells

Abstract: The direct methanol fuel cell is based on the electro-oxidation of an aqueous solution of methanol in a polymer electrolyte membrane fuel cell without the use of a fuel processor. The electro-oxidation of methanol occurs on platinum-ruthenium catalyst at the anode and the reduction of oxygen occurs on platinum catalyst at the cathode. After the initial concept development at the Jet Propulsion Laboratory (JPL), there has been considerable development of methanol fuel cell (DMFC) technology at the JPL and at various other institutions under programs sponsored by DOD and DOE. Significant improvements in power density, efficiency, and life have been demonstrated at the cell and stack level. These advances in the performance of direct methanol fuel cells are sufficiently attractive for the design of complete power systems. Portable power sources, in the range of 50-150 W, based on this technology are currently being considered for various military applications. The development of a 150 W direct methanol fuel cell power system is being pursued at the Jet Propulsion Laboratory (JPL) under DARPA funding. This paper summarizes some of the progress in the development of cells, stacks and systems.

Method and device for operating a direct methanol fuel cell with gaseous fuel

Abstract: The invention relates to a method for operating a direct methanol fuel cell. A cooling agent is vaporised in the fuel cell and a methanol-water mixture is vaporised in a vaporiser (V1). Excess heat from the fuel cell is used for vaporising the methanol-water mixture. Said vaporised methanol-water mixture is then conveyed to the anode chamber of the fuel cell. The invention also relates to a device with a direct methanol fuel cell. A cooling agent line is located in the direct methanol fuel cell and a vaporiser is provided. A fuel supply line delivers fuel to the vaporiser. Fuel which has vaporised in the vaporiser is then conveyed into the anode chamber of the fuel cell by a line. Elements are provided for transferring the excess heat from the fuel cell to the vaporiser.

Fuel cell concentration sensor

Abstract: The measuring range of a fuel cell based concentration sensor can be extended by decreasing the load across the fuel cell terminals and by increasing the amount of oxidant supplied to the fuel cell. In this way, such a sensor avoids saturation, for example, when measuring methanol concentrations from 0 M to over 4 M in liquid aqueous solution. Such a sensor is suitable for use in measuring fuel concentrations in the recirculating fuel stream of certain fuel cell stacks (for example, direct methanol fuel cell stacks).

Electrode treatment method for improving performance in liquid feed fuel cells

Abstract: Fuel cell performance in liquid feed fuel cells with an electrode comprising a carbonaceous substrate and an electrocatalyst can be increased by oxidizing the carbon substrate, particularly by electrochemical methods in acidic aqueous solution, prior to incorporation of the electrocatalyst. The treated substrate may thereafter be advantageously impregnated with a proton conducting ionomer to prevent excessive penetration of the applied catalyst into the substrate. The treatment method is particularly effective for direct methanol fuel cell anodes.

Method for preparing electrode for fuel cell and direct methanol fuel cell using the same

Abstract: PROBLEM TO BE SOLVED: To provide a method for preparing an electrode for fuel cell containing a Raney nickel having high catalytic activity, and a direct methanol fuel cell using the same. SOLUTION: A method for preparing an electrode for a fuel cell comprises the steps of bringing a mixture (a) containing a metal particle including a platinum group element (A) in contact with a metal element (B) a ionization tendency higher than that of hydrogen and a solid polymer electrolyte with a aqueous solution and removing the metal element (B) from the mixture (a). An electrode prepared by this method is used for a direct methanol fuel cell. COPYRIGHT: (C)2001,JPO

A Fuel Control Strategy that Optimizes the Efficiency of a Direct-Methanol Fuel Cell in an Automotive Application

Abstract: Author(s): Moore, Robert; Gottesfeld, Shimshon; Zelenay, P | Abstract: For automotive applications, it is necessary to maximize the fuel conversion efficiency of a PEM direct-methanol fuel cell (DMFC) over the broadest possible dynamic range of power. The research reported here critically examines the efficiency of the DMFC stack when operated over a broad power range. This research establishes a basis for a control strategy that simultaneously: optimizes DMFC fuel conversion efficiency versus power level, leads into a system level optimization of efficiency vs. power, and provides an operational strategy for controlling a direct-methanol fuel cell for maximum fuel efficiency from minimum to maximum power demand.First, there is an explanation of the experimental conditions used to obtain the DMFC experimental data that is reported and analyzed. Next the DMFC methanol crossover phenomenon is discussed and characterized. Then the conceptual framework for the optimization of fuel conversion efficiency is presented. Finally, the optimized fuel conversion efficiency is viewed in terms of the conventional voltage efficiency and fuel utilization parameters traditionally used for direct-hydrogen and reformate fuel cells.The primary conclusion of the research is that, at a given DMFC fuel consumption rate, the DMFC power density and fuel conversion efficiency is maximized by simultaneously controlling both the concentration and flow rate of the methanol fuel. This yields an optimized efficiency curve (vs. power level of DMFC operation). An additional optimization of the air flow and pressure conditions is clearly also possible, but is not explicitly developed as part of the research reported in this paper.A key feature of the optimized fuel efficiency curve is its relative flatness versus power density (e.g., greater than 30% efficiency over a range from about 70 to 230 mW cm2). The major operational result is that it is conceptually possible to optimize the conversion efficiency of a DMFC power system by manipulating the methanol fuel feed stream as a function of the system power demand. Practical application of such a strategy, of course requires a variable concentration, variable flow methanol fuel control technology.