Direct Electrochemical Fabrication Of Nanomaterials And Electrochemical Biosensor

Based on the recent progress on the preparation and applications of nano-structured materials, several novel nano-structured materials were fabricated on the surface of glassy carbon electrode (GCE) using newly designed techniques involving electrochemical deposition processes. The surface morphology and composition of the prepared materials were well characterized using various techniques. Electrocatalytic activity and electrochemical sensing ability of these materials was examined for fuel cell applications and electrochemical sensors. The dissertation includes following five sections:A nano-thickness porous Pt_0.9Pd_0.1 alloy film with a greatly enhanced surface area were firstly synthesized at GCE using a facile cyclic voltammetry (CV). It was found that the alloy film was in nanoporous structure and consisted of crystallites of 10.1 nm on average. The as-prepared electrode (Pt_0.9Pd_0.1/GCE) has an effective surface area as large as 790 times that of a corresponding bare Pt disk electrode, and has significantly higher stability and catalytic activity for both of the methanol electro-oxidation reaction (MOR) and the oxygen electro-reduction reaction (ORR) than the correspondingly nano-Pt modified GCE. We also found that the atomic ratio of the alloy can be tuned by altering the composition of the electrodeposition solution, and small amount of alloying Pd can significantly enhancing the catalytic activity of the Pt alloy, and 10% Pd is the optimal.Pt nano-clusters (nano-Pt) have been selectively attached to the open ends of mild-oxidated multi-wall carbon nanotubes (MWCNTs) by CV deposition at GCE. The excellent electrocatalytic activity of the as-prepared electrode was found for ORR and MOR. The electrocatalytic activity has been well tuned by varying the CV cycle number and the PtCl₆^2- concentration of the deposition solution. The optimal was found for the nano-Pt in average size of 100-150 nm, which consisted of nano-crystallite of an average size of 10.8 nm. The mechanism for the CV deposition is proposed. The nano-Pt deposition may be an alternative technique for wiring of nano-wires in nano-technology. The use of large sized nanoclusters (100-150 nm) as electrocatalyst may open a new opportunity for fuel cell applications.A novel composites of MWCNTs and polypyrrole (PPy) were synthesized by a method involving one-step electrochemical deposition from a thin-layer of ionic liquid solution (ILS) attached on the surface of GCE. The capacitance property of the prepared electrode were investigated by CV and chronopotentiometry. It shows that the PPy/MWCNT composites have a porous 3-D nanostructure, with high specific capacitance of 890 F/g (for the mass of PPy deposited) with high stability. The advantage of this approach was attributed to the oriented deposition of MWNT in the thin-layer ILS. This novel technique can be expected to have further applications in composite synthesis.A cysteamine (Cys) grafted GCE was firstly prepared in ILS. Gold nanoparticles (GNPs) of 20±5 nm diameter were self-assembled on the Cys grafted GCE and then glucose oxidase (GOx) was adsorbed on the top, giving a glucose biosensor GOx/GNPs/Cys/GCE. The immobilized GOx displays a pair nearly reversible redox peaks in pH 7 phosphate buffer solution (PBS) with a heterogeneous electron transfer rate constant (k_s) of 12.8 s^-1. The biosensor has excellent sensing ability to glucose with an apparent Michaelis-Menten constant of 12.0 mM of GOx. The advantage of the biosensor may be attributed to the grafted Cys layer that play important roles of electron transfer as a molecular nano-wire connecting and separating GNPs at a suitable distance for reducing the bulk effect of the block GCE.Finally, a DNA film was electrodeposited on GCE. The prepared electrode displays a novel pair of well defined and nearly reversible redox peaks at E_m of-0.114 V vs SCE in pH 7 PBS, and has excellent electrocatalytic activity toward ORR and redox reactions of H₂O₂.