The Porous Structure Design of Catalyst Layer by Controlling Particle Size Distribution of PEMFC Catalyst Ink

Abstract

A general catalyst ink of proton exchange membrane fuel cells(PEMFC) consists of a catalyst, its support, an ionomer, and a solvent. These elements are made in the form of membrane electrode assembly(MEA) through grinding, dispersing, and coating processes. Therefore, the preparation of catalyst ink is an important step that directly affects the structure formation of the catalyst layer and the cell performance. In this study, by controlling the particle size distribution of the catalyst ink, we aim to achieve optimized pore structure in the catalyst layer that leads to improved performance of the fuel cell. Particle size and its distribution of the catalyst ink were confirmed by using particle size analyzer(PSA). Mercury intrusion porosimetry(MIP) was used to determine porous structure, including the pore diameter and total pore volume of MEA. Segmented tomographic evaluation is utilized to evaluate the 3D porous carbon structure in terms of local surface area, pore size distribution, and their 3D networking. MEA were tested to ascertain the influence of the catalyst ink properties on electrochemical character such as H2/air polarization curves, electrochemical impedance spectroscopy(EIS). Also, to analyze the resistance contributed by the molecular and Knudsen diffusion and permeation through the ionomer film, we tested MEA using limiting-current measurements. As a result, We are able to confirm that the particle size has a high correlation with the pore characteristics of the electrode layer that affect the cell performance. The enhanced electrochemical performance is attributed by decreasing fine particles about 0.1um in size. We figured out that the gas diffusion resistance in the catalyst layer increases as the fine particles increase. The results of this study will provide important insights into the design and fabrication of the catalyst layers in PEMFCs and could potentially lead to improvements in the efficiency of fuel cells.