Reliability of the spherical agglomerate models for catalyst layer in polymer electrolyte membrane fuel cells

International Journal of Hydrogen Energy

et al. 2014

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The hydrophobic microporous layer (MPL) in PEM fuel cell improves water management but reduces oxygen transport. We investigate these conflict impacts using nanotomography and porescale modelling. The binary image of a MPL is acquired using FIB/SEM tomography. The water produced at the cathode is assumed to condense in the catalyst layer (CL), and then builds up a pressure before moving into the MPL. Water distribution in the MPL is calculated from its pore geometry, and oxygen transport through it is simulated using pore-scale models considering both bulk and Knudsen diffusions. The simulated oxygen concentration and flux at all voxels are volumetrically averaged to calculate the effective diffusion coefficients. For water flow, we found that when the MPL is too hydrophobic, water is unable to move through it and must find alternative exits. For oxygen diffusion, we found that the interaction of the bulk and Knudsen diffusions at pore scale creates an extra resistance after the volumetric average, and that the conventional dusty model substantially overestimates the effective diffusion coefficient.

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Section: Fib/sem Imagingmentioning

confidence: 99%

Section: Oxygen Diffusion and Effective Diffusion Coefficientmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Modelling water intrusion and oxygen diffusion in a reconstructed microporous layer of PEM fuel cells

International Journal of Hydrogen Energy

et al. 2014

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“…Since oxygen reaction in the catalyst layer depends on oxygen diffusion from the inter-agglomerate pores into the intra-agglomerate pores, which in turn depends on the agglomerate geometry, the spherical model is inadequate to describe oxygen reduction when oxygen diffusion becomes a limiting factor. In fact, recent work has shown that when approximating the oxygen reaction in a given catalyst layer using the spherical model, its agglomerate diameter is just a fitting parameter rather than a geometrical description of the agglomerates; the value of its agglomerate diameter needs to change with overpotential in order to correctly describe the average reaction rate [15,16].…”

Section: Introductionmentioning

confidence: 98%

A proposed agglomerate model for oxygen reduction in the catalyst layer of proton exchange membrane fuel cells

et al. 2014

Electrochimica Acta

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Citation: ZHANG, X. ... et al, 2014. A proposed agglomerate model for oxygen reduction in the catalyst layer of proton exchange membrane fuel cells. Electrochimica Acta, 150, pp.320 328. Additional Information:• This is the author's version of a work that was accepted for publication in Electrochimica Acta. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Oxygen diffusion and reduction in the catalyst layer of PEM fuel cell is an important process 3 in fuel cell modelling, but models able to link the reduction rate to catalyst-layer structure are 4 lack; this paper makes such an effort. We first link the average reduction rate over the 5 agglomerate within a catalyst layer to a probability that an oxygen molecule, which is 6 initially on the agglomerate surface, will enter and remain in the agglomerate at any time in 7 the absence of any electrochemical reaction. We then propose a method to directly calculate 8 distribution function of this probability and apply it to two catalyst layers with contrasting 9 structures. A formula is proposed to describe these calculated distribution functions, from 10 which the agglomerate model is derived. The model has two parameters and both can be 11 independently calculated from catalyst layer structures. We verify the model by first showing 12 that it is an improvement and able to reproduce what the spherical model describes, and then 13 testing it against the average oxygen reductions directly calculated from pore-scale 14 simulations of oxygen diffusion and reaction in the two catalyst layers. The proposed model 15 is simple, but significant as it links the average oxygen reduction to catalyst layer structures, 16 and its two parameters can be directly calculated rather than by calibration.

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“…This makes simulation of oxygen diffusion and reduction in a real CL feasible, and can be used to directly calculate the electrochemical reaction rate without need to simplify the CL structure [30,31]. The concern over this direct method is its computational cost.…”

Section: Introductionmentioning

confidence: 99%

Method to improve catalyst layer model for modelling proton exchange membrane fuel cell

Journal of Power Sources

et al. 2015

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