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Colloidal nanoparticle method for the synthesis of stable nanostructured electrocatalysts

Wet chemical methods predominantly rely on so called “bottom-up syntheses” of metal nanoparticles. The advantages are that one can control the sizes of the generated nanoparticles and also their monodispersity by the reaction conditions. The two general methods to prevent particle agglomeration are 1. electrostatic and 2. steric stabilizationL
Electrostatic stabilization is brought about by the Coulombic repulsion between particles, caused by the electrical double layer formed by ions adsorbed at the particle surface (e.g. sodium citrate) and the corresponding counter ions on a metal particle surface. Steric stabilization, in contrast is achieved via the co-ordination of sterically demanding organic molecules at the metal surface that act as protective shields. Consequently, the nanometallic cores are separated from each other thus agglomeration is prevented.

The distinct advantage of having these colloidal nanometal particles is that, they can be readily dispersible in various solvents enabling them to be laid on any given support. While preparation of colloidal catalyst precursors of controlled particle size, shape and structure can be achieved at the synthetic step, the colloidal catalyst preparation, in addition, offers ways to fine tune the electrocatalyst properties during deposition of nanoparticles on supports.

The so-called "precursor-concept", developed in our laboratories, facilitates tailoring of precursors with controlled structures as well as control of the interface between metals. Homogeneous alloys, segregated alloys, layered bimetallics, and "decorated" particles are all readily accessible using this step of catalyst synthesis. The primary incentive for using this technique is that it is possible to pre-prepare and thoroughly characterize the active components of electrocatalysts using modern analytical techniques.

Several mono, bi- and trimetallic nanoparticulate colloids were prepared (particle sizes between 1-4nm) by co-reduction and surface doping to generate particles having bulk alloy, core-shell or even gradient morphology, while applying alkalitriethylhydroborate or tetraoctylammoniumtriethylhydroborate trialkylaluminum as reducing agents.

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Forschungszentrum Karlsruhe
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