Structurally-controlled nanomaterials for fuel cell catalysis and biomedical applications

Nanomaterials e.g. nanoporous metals (NPM) and nanoparticles (NPs) feature unique chemical and physical properties and make excellent candidates for catalysis, sensing, biomedicine etc. While NPs are generated through chemical synthesis, electrochemical deposition, vapor deposition, etc, NPM obtained through dealloying are gaining more attention as alternatives to NPs due to ease of fabrication, synthetic control, structural reproducibility, and enhanced conductivity. The focus of this dissertation is the development and implementation of electrochemical routes for synthesis, characterization and testing of nanoporous catalysts. An effort is made to understand structural and compositional factors associated with the dealloying behavior and surface area evolution of different types of AuxAg(1-x) alloys; bulk samples (single and poly crystals), thin films, large spherical particles and NPs. The dealloying critical potential differs according to the crystallinity and curvature of the alloys. All samples except NPs develop significant area increase upon dealloying. A green electrodeposition bath for AuxAg(1-x) alloy deposition is established using thiosulfate electrolyte. Then a set of electrochemical routines is employed for the synthesis of platinized nanoporous Au (Pt-NPG) catalyst on gold (Au) and glassy carbon (GC) electrodes. Platinization by 1-2 nm thick layers is sufficient to cover the NPG surface completely. NPG surface area is retained after platinization. Pt-NPG are tested in formic acid oxidation reaction, current densities of ~50 mA cm-2 , mass activities of ~3 A mg-1 (of combined Pt-Au catalyst) and durability of over 2600 cycles are observed. Activities aimed at densification of the AuxAg(1-x) cluster network normally deposited on GC to a nearly continuous structure are explored by seeding GC with Cu, Ag, Pd and Au using electroless and electrodeposition approaches prior to alloy electrodeposition. The best overall results are obtained by Pd and/or Au seeding. The growth mechanism of highly monodispersed Au NPs via seeded growth method in aqueous media is explored. Particle size, morphology and optical properties of Au NPs are determined as a function of reaction time and seed/precursor concentrations. A quantitative correlation relying on dependence between the final size and the seed/precursor concentration that allows for precise NP size control is established. An aggregative growth mechanism is confirmed.