DMFCs cells

Figure 13. Comparison of oxygen electrode performance in H2-02 PEMFC and DMFC ( ) potential of the H2-O2 PEMFC cathode, (o) potential of the DMFC cathode, (A) DMFC cell potential.

Fig. 58 Air-breathing DMFC cell array and methanol cartridge integrated into the handle of an RFID tag reader made by Intermec, Inc.

Padmanabhan Srinivasan of MTI Microfuel Cells performed the computer calculations of PEFC and DMFC cell characteristics for this chapter. 

Fig. 3.4 A prototype of micro-DMFC cell (a) pictures of a planer cell (left) and its holder with terminal pins (right), and (b) a diagram of experimental apparatus for electrochemical measurements [16, 17]. Reproduced with permission of the Electrochemical Society of Japan and Elsevier...

Dimensional requirements for critical components for DMFC devices using methane as fuel are strictly dependent on the electrical power-generating capacity of the cell. DMFC cell designers recommend the typical dimensions for various components as shown in Table 3.12. 

FIG. 3.43 Comparison of DMFC cell performances between Nafion 117 and the blend membrane of SPS2.5/SPPO2 5 (5 5, w/w). (Reprinted with permission from Elsevier (2004). Copyright 2004 Elsevier [427].)... 

The final application for most of the hybrid/composite membranes is focused on PEM fuel cells, especially for DMFCs. Cell performance study, about which power density can be calculated at a particular voltage, RH, and temperature, is the main evaluation method for membrane final potentials. Table 9.7 gives an overview of the current densities measured for various membranes under different experimental conditions. 

The schematic diagram of the liquid-feed direct methanol fuel cell (DMFC) is shown in Figure 13.1. 

Fuel cells can run on fuels other than hydrogen. In the direct methanol fuel cell (DMFC), a dilute methanol solution ( 3%) is fed directly into the anode, and a multistep process causes the liberation of protons and electrons together with conversion to water and carbon dioxide. Because no fuel processor is required, the system is conceptually vei"y attractive. However, the multistep process is understandably less rapid than the simpler hydrogen reaction, and this causes the direct methanol fuel cell stack to produce less power and to need more catalyst. 

The dynamic behavior of fuel cells is of importance to insure the stable operation of the fuel cells under various operating conditions. Among a few different fuel cell types, the direct methanol fuel cell (DMFC) has been known to have advantages especially for portable... 

The transient response of DMFC is inherently slower and consequently the performance is worse than that of the hydrogen fuel cell, since the electrochemical oxidation kinetics of methanol are inherently slower due to intermediates formed during methanol oxidation [3]. Since the methanol solution should penetrate a diffusion layer toward the anode catalyst layer for oxidation, it is inevitable for the DMFC to experience the hi mass transport resistance. The carbon dioxide produced as the result of the oxidation reaction of methanol could also partly block the narrow flow path to be more difScult for the methanol to diflhise toward the catalyst. All these resistances and limitations can alter the cell characteristics and the power output when the cell is operated under variable load conditions. Especially when the DMFC stack is considered, the fluid dynamics inside the fuel cell stack is more complicated and so the transient stack performance could be more dependent of the variable load conditions. 

In this paper we report the effect of varying loads on a small size DMFC stack (10 cells with 9 cm active-area each). The transient responses of the stack voltage have been investigated upon variable current load conditions to obtain the information on the dynamic characteristics of the stack. Also, the transient responses of the stack current upon changing fuel flow rates have been monitored to obtain the optimal operating conditions for the staek. 

The DMFC used in this study was a 10-cell stack with 3cm X 3cm active area (total active... 

The electrocatalytic oxidation of methanol has been widely investigated for exploitation in the so-called direct methanol fuel cell (DMFC). The most likely type of DMFC to be commercialized in the near future seems to be the polymer electrolyte membrane DMFC using proton exchange membrane, a special form of low-temperature fuel cell based on PEM technology. In this cell, methanol (a liquid fuel available at low cost, easily handled, stored, and transported) is dissolved in an acid electrolyte and burned directly by air to carbon dioxide. The prominence of the DMFCs with respect to safety, simple device fabrication, and low cost has rendered them promising candidates for applications ranging from portable power sources to secondary cells for prospective electric vehicles. Notwithstanding, DMFCs were... 

Although ORR catalysts for DMFCs are mostly identical to those for the PEM fuel cell, one additional and serious drawback in the DMFC case is the methanol crossover from the anode to the cathode compartment of the membrane electrode assembly, giving rise to simultaneous methanol oxidation at the cathode. The... 

PAFC, phosphoric acid fuei ceii MCFC, moiten carbonate fuei ceii SOFC, soiid oxide fuei ceii PEMFC, proton exchange membrane fuei ceii DMFC, direct methanoi fuei ceii AFC, alkaiine fuel cell. 

In the United States, the Department of Defense (DOD) and the Department of Energy (DOE) promoted in 1992 the Defense Advanced Research Project Agency (DARPA) program to develop a DMFC for portable and mobile applications. Several institutions are involved (IFC, JPL, LANE, Giner, Inc.) and small stacks (up to 10 elementary cells) were built by IFC and JPL. The performances are quite encouraging, with power densities of 250 mW/cm at 0.5 V. More details are given in Section V.2. 

The enthusiasm for developing DMFCs (the fuel cell researcher s dream) evolved in the 1960s, which was really the boom period for R D activities on all types of fuel cell technologies, mainly because of NASA s vital need for fuel cell power plants for space vehicles. As early as the 1960s it was recognized that the major challenges in developing DMFCs... 

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