Increasing Activity of Trimetallic Oxygen Reduction PtNiMo/C Catalysts Through Initial Conditioning

This study investigates the importance of preconditioning in Pt-alloy catalysts for oxygen-reduction reactions. Previous research indicated that slower scanning rates during preconditioning initially boost activity, but this is followed by a rapid decline. The study reveals the required number of cycles to achieve the first constant steady state activity in PtNiMo/C catalysts when using slower scanning rates during preconditioning. It also highlights the resulting activity differences. Remarkably, a catalyst preconditioned with 150 slow cycles showed an activity of approximately 1.25 mA cm-2 at 0.90 VRHE, significantly higher than one preconditioned at a fast rate (0.82 mA cm-2). Both ex-situ and in-situ analyses revealed that Pt, along with Ni, was leached during pretreatment. At slower scan rates of 20 mV s-1, the dissolved Pt redeposited as highly active, small-sized clusters or single atoms. Fast scan rates of of 500 mV s-1, in contrast, resulted in fewer such clusters. Accelerated stress tests up to 1.10 VRHE confirmed the high stability of these clusters, demonstrating a substantial activity increase even after 24,000 cycles. Chances in the preconditioning of Pt alloy catalysts have a huge impact to the specific activity outcome. A slow pretreatment at 20 mV s-1 results in a fast increase, strong drop and reaching nearly steady state activities at high cycle numbers. Alongside a change in the octahedral PtNiMo/C catalyst to Pt clusters is observed. image