Rheological Study of Electrode Ink for a PEMFC: I/C and Solid Content

Facilitating cost reduction and durability improvement of the next-gen PEMFCs requires focused efforts on not only advanced catalyst materials but also optimized electrode design concepts 1,2 . Currently, the most widely used electrode in a PEMFC is made from ink dispersion consists of catalyst, catalyst support, ionomer, and solvent. Before advancing optimized electrode design, the desired properties of the electrode ink dispersion and its corresponding relationship to catalyst layer need to be studied 3 . In our previous work, we have used rheological measurements as a tool to study a baseline electrode ink with Pt/C and Nafion ionomer. The strength, tortuosity and structural character of electrode ink were quantitatively and qualitatively characterized by oscillation amplitude sweep and frequency sweep. The flow property of the catalyst inks was measured by viscometry. A coating process was also simulated and its impact on the ink microstructure was investigated as well. With our preliminary results from the oscillatory and viscometry tests, we proposed physical models to describe Pt/C-ionomer agglomerate as the microstructural unit in various water/IPA binary solvents. These collective data also verify a strong correlation between the electrode ink rheology and its resulting microstructure, which allowed us to speculate the Pt/C-ionomer agglomerate structure in the opaque electrode inks. The rheological characterization of electrode ink not only enhances our fundamental understanding of the electrode formation, but also provides valuable information for electrode optimization. Built upon the foundation of our previous work, we employed an improved approach to study ionomer to carbon ratio and solid content in the electrode ink in this work. The main objective is to improve fuel cell performance through optimization of electrode ink. This comprehensive study allows us to understand the adsorption behavior of ionomer onto Pt/C and their impact on the microstructure of Pt/C-ionomer agglomerates. With the assist of rheological data, we were able to identify the optimal ionomer to carbon ratio for this system at different solid content. Our preliminary results showed strong interactive nature between Pt/C, ionomer content, and volume fraction. Key rheological features of the studied inks and their corresponding relationship to the electrode microstructure for performance optimization will be present at the conference. References Kongkanand A and Mathias MF. The priority and chanllenge of high-power performance of low-platinum proton-exchange membrane fuel cells. The journal of physical chemistry letters, 2016, 7, 1127-1137. Banham D and Ye S. Current status and future development of catalsyt materials and catalyst layers for proton exchange membrane fuel cells: an industrial persperctive. 2017, 2, 629-638. Hatzell KB et. al.. Understanding inks for porous-electrode formation. 2017, 5, 20527-20533.