Effect of Pt Solution Concentration during Direct Preparation of Core–Shell Pt Cathode in MEA Catalyst Layer for PEFC

Core-shell catalyst, which consists of thin Pt shell on non-Pt metal core, has been attracting attention as a low-Pt catalyst for polymer electrolyte fuel cell (PEFC). Typically, it is synthesized by using Cu-underpotential deposition (Cu-UPD) followed by surface limited redox replacement (SLRR). However, since this method is normally performed on a rotating disk electrode, it can only be prepared on a microgram scale. We have been developing a novel method to overcome this problem by directly performing Cu-UPD and SLRR to the catalyst layer made from the core material. Using this method, the reaction area is increased since the reaction occurs on particles in the three-dimensional network. In our previous study, we have reported that a Pd@Pt/C catalyst layer prepared by this method shows higher mass activity than conventional Pt/C. However, deposition at the surface of the catalyst layer appeared to be larger than in the interior of the layer. In this study, the effect of Pt ion solution concentration on the Pt deposition behavior was studied to develop highly active low-Pt catalyst layer by this novel method. Pd/C was used to fabricate a catalyst layer made of core material. Cu-UPD and SLRR was performed twice on this catalyst layer. In the SLRR process, Pt ion solution with various concentration was used. When a high concentration solution was used, large deposition at the surface was apparent. On the other hand, when a low concentration solution was used, the deposition at the surface was suppressed but the amount of Pt deposition was insufficient. By using both the low and high concentration solution, metallic luster caused by the large depositon of Pt was not observed, and a sufficient amount of Pt was deposited. The performance of a MEA prepared by this catalyst layer showed higher performance than that prepared by the previously reported method.