UC Merced

Proton exchange membrane fuel cell (PEMFC) technology provides a sustainable power solution as it electrochemically converts the chemical energy stored in hydrogen molecules into electricity, heat, and water. The electrochemical reactions occurring in the catalyst layer (CL), however, requires the use of precious group metal (PGM) catalysts, such as platinum, which is a major factor contributing to the high cost of PEMFC technology. To reduce the cost, there have been extensive research efforts in developing low-PGM and PGM-free catalyst materials. Nevertheless, the CLs incorporating these novel materials are often found to suffer from severe mass transport resistance resulting in significant performance loss. Based on the literature, this undesired mass transport resistance is mainly attributed to the cathode oxygen transport due to the heterogeneous characteristics of the hierarchical microstructure of the CL. Although a standard CL only contains carbon supported catalyst and ionomer, understanding the formation of the structure and the origin of the structural characteristics have been very challenging due to its complicated preparation process. A CL is usually prepared by an ink casting method, which involves multiple steps. The catalyst ink consists of the CL constituent materials uniformly dispersed in a liquid medium forming a suspension, which has an opaque, heterogeneous, and highly time-sensitive nature making the experimental investigation on the particulate structure in the catalyst ink very challenging. Despite the long history of using the CLs, a principled framework for understanding the structure-property relationship of the CLs has not yet fully developed. To advance the design and development of low-cost and robust CLs, this research 1) conceptualized a physical process capturing the key aspects of the particulate structure formation with respect to the CL fabrication process, 2) based on the complex fluid nature of the catalyst ink, designed a holistic non-destructive hierarchical approach to investigate the particulate structure in the catalyst ink, and 3) qualitatively and experimentally established the formation-structure-process-functionality relationship for CLs. With the newly proposed framework, this research advances current understanding on the structure-property relationship of the CLs and provides novel and practical insights into the design of low-cost functionality-tailored CLs.