The Influence of Ionic Liquid Modification on the Restructuring of Trimetallic PtNiMo/C Catalysts During Conditioning

During preconditioning of PtNiMo/C catalyst metal dissolution and redeposition takes place. At slow scan rates this leads to increased steady activity for oxygen reduction reaction (ORR). Furthermore, ionic liquids (IL) influence the activity of Pt-based catalysts and can alter the leaching of Pt-alloy catalysts. This study investigates the influence of ILs on the preconditioning of PtNiMo/C catalysts. Therefore, preconditioning parameters as well as the IL employed were varied. ILs with long side chains like [C8fC1][BETI] resulted in a spreading of the activity development during preconditioning over a longer cycle time and with damped amplitude for the activity changes. For shorter side chains like [BMIM][BETI] the development is like the pristine catalyst. Ex-situ and in-situ characterization revealed that [BMIM][BETI] leached fast to the electrolyte, which was not observed for the other ILs. Nevertheless, for all ILs a strongly reduced platinum leaching was observed. Even for the leached [BMIM][BETI] a stable wetting layer influencing the leaching seems to remain. Nevertheless, only for the other ILs where an immobilized bulk phase is remaining a difference in catalyst restructuring during the preconditioning is observed and a higher number of small sized Pt clusters and a lower amount of bigger Pt clusters resulted.