Halide‐Induced Leaching of Pt Nanoparticles – Manipulation of Particle Size by Controlled Ostwald Ripening

Abstract

The synthesis of "surfactant-free" Pt nanoparticles (NPs) in alkaline ethylene glycol (EG), initially introduced in 2000, is of fundamental interest for the preparation of catalysts. Often a suspension of colloidal Pt NPs prepared by this method is stored and upon demand further processed to obtain supported catalysts such as PtÀC or PtÀAl 2 O 3 . In this study it is shown that in such colloidal suspensions in the presence of halides, e. g. from the metal precursor salt, leaching of Pt NPs takes place. Metal leaching poses a significant challenge for catalyst stability. However, if the reaction conditions are chosen appropriately, the here identified leaching process can be utilized to achieve particle growth by Ostwald ripening in a controlled manner. By changing the chemical nature of the metal precursor salt and variation of the reaction time, Pt NPs with a narrow size distribution between 1 to 4 nm are obtained without any need of surfactants. Subsequently, the obtained particles can be transferred into low-boiling organic solvents, which then allows for coating of deliberately chosen supports to prepare e. g. model catalyst which are tailored in terms of particle size and support material. The suitability of such materials for catalytic investigations is demonstrated by using CO oxidation as a model reaction and it is shown that the catalytic activity (surface normalized) depends on the size of Pt NPs under the applied reaction conditions.[a] S.

Beyond Active Site Design: A Surfactant‐Free Toolbox Approach for Optimized Supported Nanoparticle Catalysts

“…The synthesis can be induced in various ways including using thermal sources (oil bath synthesis at ca. 160 °C), [31,33] micro‐wave, [34] UV‐light, [35,36] or even ambient conditions [37] . The as‐prepared NPs can be functionalized, e. g. by phase transfer reaction with lipophilic ligands (transfer into toluene) [31] .…”

“…The (long term) storage of colloids is a non‐trivial task. It was shown that the presence of residual halides in the synthesis could lead to NP leaching in the liquid phase [33] . Unprotected NPs are mainly functionalized with CO and HO − groups [47] .…”

Surfactant-Free Colloidal Strategies for Highly Dispersed and Active Supported IrO2 Catalysts: Synthesis and Performance Evaluation for the Oxygen Evolution Reaction

“…However, a reported benefit of EG is the stability of its colloidal dispersions against flocculation. 29,30 Thus, to evaluate the colloidal stability, the as-prepared Ir NPs synthesized using MeOH and EtOH as solvent have been characterized by their Z-potential, see Figure 1. It is found that the colloidal Ir NP suspension prepared in MeOH exhibits a higher absolute Z-potential than the one prepared in EtOH.…”

“…Moreover, when re-dispersed in acetone, the suspension cannot be stored for a long time since Ir NPs seem to dissolve back very slowly to complex species forming a yellow solution, as previously observed for Pt NPs treated in the same manner. 30 In the next step, for each solvent (EtOH, MeOH, and EG) a series of Ir/C catalysts with different metal loadings, i.e., 10, 30, 50, 70 wt.% was prepared. We then determined the mean nanoparticle diameter of the different supported catalysts via SAXS.…”

An introduction to electrochemical energy conversion

“…7 with fig. 8, which has been obtained from a "real" catalyst by the Arenz group, who have worked intensively on studying platinum nanoparticles in electrocatalysis [40][41][42]. Nanoparticles are favored as catalysts in fuel cells due to their high catalytic activity and high surface to volume ratio, allowing for very low amounts of the expensive material (we shall come back to this later).…”