Cathode catalyst layer design with gradients of ionomer distribution for proton exchange membrane fuel cells

Cathode catalyst layer (CCL) design is critically important for improved performance, durability and stability of proton exchange membrane (PEM) fuel cells. In this study, CCL is designed to consist of two sub-layers with different loadings of short-side chain (SSC) ionomer and platinum (Pt) catalyst for each sub-layer; and such CCLs are manufactured and characterized through morphological, microstructural, physical, and electrochemical characterizations, and the performance of single scaled-up cells containing such CCL designs is measured. The results show that the two-layer design results in a higher porosity and mean pore size, and hence higher air permeability, and provides distinctively higher catalyst activity and Pt utilization for the CCL than the conventional single-layer design under the same overall loadings of the ionomer and Pt for the entire CCL. It is also found that a higher ionomer loading in the first sub-layer (faced to the membrane) is beneficial to cell performance, and the Pt loading in this sub-layer plays a considerably important role as well. Overall, it is demonstrated that with a proper ionomer/Pt-gradient design, it is possible to achieve favorable morphological and microstructural characteristics that lessen ionic resistance while improving mass transport capability, catalyst activity, and Pt utilization, hence overall cell performance.