Self-Organization in Catalyst Layers Concluding Remarks

Self-Organization in Catalyst Layers Concluding Remarks 

CGMD simulations have become a viable tool in studying self-organization processes in catalyst layers of PEFCs. Stmctural parameters of interest for such studies involve composition and size distributions of Pt/C agglomerates, pore space morphology, surface wettability, as well as the structure and distribution of ionomer. The latter aspect has important implications for electrochemically active area, proton transport properties, and net electrocatalytic activity of the CL. 

The morphology of ionomer aggregates in CL is clearly different from that in the PEM, even if the base ionomer is the same. A simple extrapolation of ionomer properties in CLs, from properties of the bulk PEM, using percolation theory is generally insufficient. Ionomer forms a thin adhesive skin layer at agglomerate surfaces with undetectable internal porosity. The Pt loading could play a significant role in the transition of pore surface properties from hydrophobic to hydrophilic. 

Evolution of the stmctural attributes of CLs through self-organization is particularly important for the further analysis of the transport characteristics of protons, electrons, reactant molecules (O2), and water. This encompasses the distribution of electrocatalytic activity at Pt-water interfaces. In principle, mesoscale simulations can establish relations between these characteristics and the intrinsic properties of various solvents, carbon materials, and ionomer materials. They can also help clarify the dependency of these characteristics on the gravimetric composition and the level of hydration. There is still a lack of comprehensive experimental data, with which simulation results could be compared. Versatile experimental techniques have to be employed to study particle-particle interactions, stmctural characteristics of phases and interfaces, and phase correlations of carbon, ionomer, and water. 

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