Electrodeposited metal nanostructures fabricated by dynamic hydrogen bubble templating
Creators: name: Oppedisano, Daniel
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 340601
subject: Catalysis and mechanisms of reactions
classificationCode: 340604
subject: Electrochemistry

description: The thesis describes the preparation of a range of nanostructured films utilising electrodeposition at high overpotentials, where metal deposition is accompanied by the evolution of hydrogen (H2) bubbles, by a method termed Dynamic Hydrogen Bubble Templating (DHBT). The DHBT method provides a versatile route to a range of nanostructured, highly porous, high surface area metallic materials through the use of H2 bubbles as a template. Materials can be produced with controlled surface properties including morphology, composition, porosity and electronic environment with the two factors that are important in controlling morphology are the H2 bubble behaviour and the metal nucleation and growth during electrodeposition.<br><br>It was shown that changes in the hydrodynamic conditions during electrodeposition can be used to force metals with slow deposition kinetics into diffusion limited growth regimes. Ruthenium was electrochemically deposited as dendrites for the first time. The turbulent conditions caused by the H2 bubbling compresses the diffusion layer, which when combined with the high overpotential, allowed access to the dendritic morphology.<br><br>The DHBT method reliably formed a porous gold (Au) nanostructured honeycomb film, which was directly compared with model Au nanoparticles for activity towards the sulfur dioxide (SO2) oxidation reaction. When compared to low index Au nanoparticles, the dendritic morphology of the Au honeycomb showed a lower overpotential for SO2 oxidation.<br><br>The DHBT method was used to prepare multimetallic films. Deposition under diffusion limited regimes overcomes kinetic limitations that arise when depositing metals with different deposition rates, which allowed for control over the noble metal content in multimetallic structures. The facile fabrication of multimetallic films occurred with the addition of small amounts Au and palladium (Pd), and Au to a copper (Cu) electrolyte. It was shown how very small amounts of noble metals could significantly change the morphology and composition, while affecting the crystal lattice of Cu. High specific surface area films were prepared with less than 5 % of noble metal content, sufficient to exhibit optimised catalytic activities. The films were found to be a solid solution, where the Cu acted as the host in which the noble metals were dissolved. It was shown that the synergism obtained by the combination of three metals (e.g. CuAuPd), was effective at increasing the catalytic activity, particularly for the hydrogen evolution reaction (HER).<br><br>Films with the addition of Au and Pt to Cu were prepared, with their catalytic activity tested for the sodium borohydride electrooxidation reaction. The small amounts of noble metals caused drastic changes to the morphology and properties of the films. The trimetallic films were more effective for model catalytic reactions compared to bimetallic films.<br><br>The thesis has studied the fabrication of a range of surfaces by DHBT, and shown that DHBT can be used to access a wide variety of different metallic nanostructures in a simple and controlled manner using H2 bubbles produced at high overpotential. These materials have good chemical and structural stability, which present themselves excellent candidates for applications in reactions where catalysts based on supported nanoparticles have suffered from long term stability problems.