A Particle Based Ionomer Attachment Model for a Fuel Cell Catalyst Layer

Abstract

A particle model for ionomer attachment on carbon black in a Polymer Electrolyte Fuel Cell (PEFC) catalyst layer was developed based the random walk method. Two different methods of particle attachment were used that resemble different catalyst ink preparation conditions: the solution method and the colloidal method. In the solution method, the simulation of attachment is conducted on the aggregate structures and in the colloid method, the attachment is simulated on the agglomerate structures. The distribution of carbon black, ionomer and void space was used in a multiscale electrochemical simulator that calculated the mass/charge transfer and reaction in the catalyst layer. The results of effective oxygen diffusion coefficients are consistent with experimental result and show why the Bruggeman correlation often is a poor approximation for upscaling the effective diffusive and conductive components in PEFC porous media. The solution method allowed for a better proton conduction through the ionomer but resulted in a thicker ionomer film that increased the oxygen diffusive resistance. However, solution and colloidal method resulted in similar cell performances. Our model can aid in the design to develop fuel cell catalyst layers with improved performance.

Electrocatalysis in Alkaline Media and Alkaline Membrane-Based Energy Technologies

“…The connectivity of the agglomerates in the catalyst layer is also an important factor in transporting ions and gaseous reactants. A bottom-up particle packing approach based on a random walk method was used to study the connectivity of carbon black aggregates in the catalyst layer. , The model predicted a fourth power dependence of the effective oxygen diffusion coefficient on the porosity, due to the combined effect of the surface morphology of the reconstructed carbon particle and Knudsen diffusion. The importance of connectivity is also experimentally confirmed by the different oxygen transport resistance in two agglomerates with the same volume and ionomer but different aspect ratios .…”

Perspectives on Challenges and Achievements in Local Oxygen Transport of Low Pt Proton Exchange Membrane Fuel Cells

“…[ 77 ] In a parallel study conducted by So et al., the ionomer coverage elevates form 50% to 95% while I/C increases from 0.2 to 2, further proving the incomplete coating of PFSA ionomer on catalyst surface. [ 78 ]…”

“…[77] In a parallel study con ducted by So et al, the ionomer coverage elevates form 50% to 95% while I/C increases from 0.2 to 2, further proving the incomplete coating of PFSA ionomer on catalyst surface. [78] As a consequence, it is essential to count the effect of ionomer coverage (θ ionomer ) when calculating R Local . As shown in Figure 6a,b, both the oxygen transport resistance in the ionomer region (R ionomer ) and the void region (R pore ) [79] should be considered, where R ionomer and R pore denote the gas transport resistance for the situation that θ ionomer is 1 and 0, respectively.…”

Distinguishing Adsorbed and Deposited Ionomers in the Catalyst Layer of Polymer Electrolyte Fuel Cells Using Contrast-Variation Small-Angle Neutron Scattering

“…The structure parameters for the adsorbed and deposited ionomers are available to validate and improve simulation of the catalyst layer performance. Some models have been proposed to simulate PEFC performance recently, where the proton diffusion and oxygen permeation are directly evaluated from tortuosity in a three-dimensional microstructure model of a catalyst layer. ,− Since the models are based on the porous structure of the carbon particles and the coating structure of the ionomer, focused ion-beam SEM and TEM tomography can provide data for construction of a catalyst-layer structure, respectively . However, the limited observation volume, elaborated sample preparation, and inevitable radiation damage require complemental methods.…”