Electron Transport in PEFCs

Meng, Hua; Wang, Chao Yang

doi:10.1149/1.1641036

Cited by 190 publications

(110 citation statements)

References 11 publications

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“…6−8 The porous electrode is required to carry the electron current from the electrocatalyst to the external circuit. 9 It must also permit transport of gas reactants and liquid product between the gas flow channels and the catalyst/PEM interface. 4,10,11 The porous electrode, or gas diffusion layer (GDL), of the fuel cell is typically made from carbon fibers, either as a random sheet of fibers in the form of carbon paper or as a woven array of fiber bundles forming carbon cloth.…”

Section: ■ Introductionmentioning

confidence: 99%

Drop Detachment and Motion on Fuel Cell Electrode Materials

Gauthier

Hellstern

Kevrekidis

et al. 2012

ACS Appl. Mater. Interfaces

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Liquid water is pushed through flow channels of fuel cells, where one surface is a porous carbon electrode made up of carbon fibers. Water drops grow on the fibrous carbon surface in the gas flow channel. The drops adhere to the superficial fiber surfaces but exhibit little penetration into the voids between the fibers. The fibrous surfaces are hydrophobic, but there is a substantial threshold force necessary to initiate water drop motion. Once the water drops begin to move, however, the adhesive force decreases and drops move with minimal friction, similar to motion on superhydrophobic materials. We report here studies of water wetting and water drop motion on typical porous carbon materials (carbon paper and carbon cloth) employed in fuel cells. The static coefficient of friction on these textured surfaces is comparable to that for smooth Teflon. But the dynamic coefficient of friction is several orders of magnitude smaller on the textured surfaces than on smooth Teflon. Carbon cloth displays a much smaller static contact angle hysteresis than carbon paper due to its two-scale roughness. The dynamic contact angle hysteresis for carbon paper is greatly reduced compared to the static contact angle hysteresis. Enhanced dynamic hydrophobicity is suggested to result from the extent to which a dynamic contact line can track topological heterogeneities of the liquid/solid interface. KEYWORDS: contact angle, hydrophobic, carbon, wetting, carbon fibers, contact angle hysteresis, Teflon ■ INTRODUCTIONWater transport is an essential element of polymer electrolyte membrane (PEM) fuel cell operation. 1−5 Liquid water that is formed at a catalyst/membrane interface is pushed through porous electrodes into gas flow channels. The water drops emerge from the largest pores in the electrode, and grow in the channel. Initially, the drops are held in place by adhesion to the water column in the electrode pore, but as the drops grow surface contact with the porous electrode and surface contact with the walls of the flow channel are the dominate adhesive forces. The drop must be detached and pushed through the gas flow channel in contact with the electrode surface to be removed from the fuel cell. Efficient fuel cell operation requires removal of liquid water drops from the fuel cell with minimal work. The surface properties of the porous electrode play a key role in the energy required to remove water drops from the gas flow channels of the fuel cell. We have been devising experiments to isolate the flow resistances for water transport through the porous electrode and gas flow channel. 6−8 The porous electrode is required to carry the electron current from the electrocatalyst to the external circuit. 9 It must also permit transport of gas reactants and liquid product between the gas flow channels and the catalyst/PEM interface. 4,10,11 The porous electrode, or gas diffusion layer (GDL), of the fuel cell is typically made from carbon fibers, either as a random sheet of fibers in the form of carbon paper or as a woven arr...

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Section: ■ Introductionmentioning

confidence: 99%

Drop Detachment and Motion on Fuel Cell Electrode Materials

Gauthier

Hellstern

Kevrekidis

et al. 2012

ACS Appl. Mater. Interfaces

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“…The volume of electrolyte attached to the surface of each agglomerate is f e /N, which, from our assumptions, covers the entire surface of the agglomerate. The thickness δ e 0 (without swelling) and f 0 are therefore related as follows − R ag (44) The electrolyte swelling results in a volume change equal to (per agglomerate) ( f e − f 0 )/N. The electrolyte film thickness is then given by…”

Section: Reaction Rate and Limiting Current Densitymentioning

confidence: 99%

“…However, as with the zero flux conditions, this implicitly assumes that the strength of the flow in the channel has no impact on the liquid water levels at the GDL surface. In [44] Meng and Wang specify the saturation at the GDL/channel interface, which, as they correctly state, depends sensitively on the gas flow in the channel, current density and wettability [45].…”

Section: Initial and Boundary Conditionsmentioning

confidence: 99%

Transient non-isothermal model of a polymer electrolyte fuel cell

Shah

Kim

Sui

et al. 2007

Journal of Power Sources

142

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“…It is common in modelling studies, for example [3,[5][6][7], to assume either a zero saturation or zero liquid-water flux at this location, or along portions of the channel/GDL interface in two dimensions. In [47], Weng and Wang specify the saturation at the GDL/channel interface, which, as they state, is likely to depend sensitively on the gas flow in the channel, current density and wettability. According to their results, high levels of saturation are possible only if the prescribed value at the boundary is high or the GDL permeability is unrealistically small.…”

Section: Boundary Conditionsmentioning

confidence: 99%

The effects of water and microstructure on the performance of polymer electrolyte fuel cells

Shah

Kim

Gervais

et al. 2006

Journal of Power Sources

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In this paper, we present a comprehensive non-isothermal, one-dimensional model of the cathode side of a Polymer Electrolyte Fuel Cell. We explicitly include the catalyst layer, gas diffusion layer and the membrane. The catalyst layer and gas diffusion layer are characterized by several measurable microstructural parameters. We model all three phases of water, with a view to capturing the effect that each has on the performance of the cell. A comparison with experiment is presented, demonstrating excellent agreement, particularly with regard to the effects of water activity in the channels and how it impacts flooding and membrane hydration. We present several results pertaining to the effects of water on the current density (or cell voltage), demonstrating the role of micro-structure, liquid water removal from the channel, water activity, membrane and gas diffusion layer thickness and channel temperature. These results provide an indication of the changes that are required to achieve optimal performance through improved water management and MEA-component design. Moreover, with its level of detail, the model we develop forms an excellent basis for a multi-dimensional model of the entire membrane electrode assembly.

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Electron Transport in PEFCs

Cited by 190 publications

References 11 publications

Drop Detachment and Motion on Fuel Cell Electrode Materials

Drop Detachment and Motion on Fuel Cell Electrode Materials

Transient non-isothermal model of a polymer electrolyte fuel cell

The effects of water and microstructure on the performance of polymer electrolyte fuel cells

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