Analysis of Catalyst Layer Microstructures: From Imaging to Performance

Image analysis and numerical simulation algorithms are introduced to analyze the micro-structure, transport, and electrochemical performance of thin, low platinum loading inkjet printed electrodes. A local thresholding algorithm is used to extract the catalyst layer pore morphology from focused ion beam scanning electron microscopy (FIB-SEM) images. n-point correlation functions, such as auto-correlation, chord length, and pore-size distribution are computed to interpret the micro-structure variations between different images of the same catalyst layer. Pore size distributions are in agreement with experimental results. The catalyst layer exhibits anisotropy in the through-plane direction, and artificial anisotropy in the FIB direction due to low slicing resolution. Microscale numerical mass transport simulations show that transport predictions are affected by image resolution and that a minimum domain size of 200 nm is needed to estimate transport properties. A micro-scale electrochemical model that includes a description of the ionomer film resistance and a multi-step electrochemical reaction model for the oxygen reduction reaction is also presented. Results show that the interfacial mass transport resistance in the ionomer film has the largest effect on the electrochemical performance.