Tuning of surface structure and particle morphology via electrochemical deposition
Synthesis and characterization of anisotropic micro- and nanoparticles, either in suspension or localized on a surface, are current areas of intense scientific interest because of their shape-tunable material properties with potential applications in catalysis, microelectronics, data storage and pharmaceutics. Electrochemical deposition represents a facile and versatile route to fabricate anisotropic particles since it offers a high degree of freedom in monitoring and manipulating particle growth processes. The first part of my dissertation presents an additive-mediated electrochemical approach to fabricate anisotropic copper micro- and nanoparticles. This work explores the possibility of using anisotropic copper particles as novel non-noble metal alternatives to expensive anode electrocatalysts (platinum and palladium) used in direct methanol fuel cells (DMFCs). Characterization using SEM, EDS, XRD and TEM confirms the anisotropic morphology and crystal structure of synthesized copper particles. A possible mechanism for anisotropic crystal growth is proposed based on preferential adsorption of additive ions onto selective crystal faces. Methanol oxidation is chosen as model experiment to test the electrocatalytic property of copper particles towards DMFC applications. Characterization using cyclic voltammetry demonstrates shape dependent enhancement in electrocatalytic activity of anisotropic copper particles for methanol oxidation. Chronoamperometry and thermal stability measurements indicate good catalyst stability and durability under steady-state conditions. The second part of my dissertation presents a novel electrochemical fabrication route to generate randomly rough surfaces over large areas. Surface roughness directly affects a material's performance at its functional interface. This work shows that by simple tuning of electrochemical deposition potential for a metal onto an electrode, island nucleation density can be systematically varied. Changes in nucleation density results in generation of thin films with different nanoscale surface roughness. Characterization using AFM illustrates the change in surface topography with applied potential. The fabricated roughness is successfully replicated onto other moldable soft materials (polystyrene and polyurethane) through an embossing and curing step. Roughness gradients were also generated by introducing a controlled mechanical retraction step to the process. Gradient surfaces serve as an effective probing tool for investigating a range of surface parameters in quick time using single experiment, enabling a cost-effective and high-throughput screening method.