Nanoelectrodes And Nanopore Electrodes: Preparation And Electrochemical Response

In recent years, nanomaterials have attracted considerable attentionin the area of biosensor, new energy resources, and biotechnology, etc.Electrochemistry and electrocatalysis at single nanoparticle level haverecently reported. It is well-known that the size of commercial probes aretoo big, and it is impossible to get images with high resolution anddetection in single molecular level. In this dissertation, nanoelectrodesand nanoporous electrodes have been prepared and the electrochemicaland electrocatalytic properties have been investigated carefully. Moreover,the applications of nanoelectrodes and nanoporous electrodes in sensingand scanning electrochemical microscope (SECM) have beeninvestigated. The details are listed below:1. Single Pt Nanowire ElectrodeA single Pt nanowire electrode(SPNEs) was fabricated through etchingprocess from Pt disk nanoelectrode and an underpotentialdeposition(UPD) redox replacement technique. The electrochemicalexperiments showed that SPNEs had steady-state electrochemicalresponses at redox species solution and the mass transfer rates wereaffected by the lengths and radii of SPNEs. The prepared SPNEs wereutilized to examine the oxygen-reduction reaction in a KOH solution toexplore the feasibility of electrocatalytic activity of single Pt nanowireand the results showed that the electrocatalytic activity of SPNEs wasdependent on the surface position of single Pt nanowire: the tip endposition is more active than the sidewall position. Meanwhile, theelectrocatalytic activity of SPNEs was related to the radius of nanowire.These observations are not only important to understand the structurefunction relationship in single nanowire level, but have significantimplications for the synthesis and selection of novel catalysts with highefficiency used in electrochemistry, energy, bioanalysis, etc.2. Electrochemistry at Nanoporous InterfacesThe permselective properties of nanoporous membranes derived from a cylinder-forming Polystyrene-b-Poly(ethylene oxide) diblock copoly-mer(PS-b-PEO) were investigated by means of cyclic votammetry(CV)and electrochemical impedance spectroscopy(EIS). The nanoporousmembranes were prepared by solvent evaporation and UV irradiationtechnique. The influence of pH and ionic strength on permselectivetransport in nanoporous films prepared from PS-b-PEO was investigatedby cyclic voltammetry in aqueous and organic solutions. The peak currentobtained from differential pulse voltammetry(DPV) was linearlydependent on the DA concentration in the range of0.1-25μM at neutralpH (PBS, pH7.0) with a correlation coefficient of0.999, and thedetection limit was0.04μM (S/N=3).3. Fabrication of Well-Organized Pt NanowiresWe present a method to obtain a dense array of well-organizedplatinum nanowires(PtNWs) on a large substrate area by using a PS-b-PEO block copolymer template. The morphologies and structure of theplatinum nanowires (PtNWs) have been characterized using scanningelectrochemical microscope(SECM), field emission scanning electronmicroscopy(FE-SEM) and cyclic voltammetry(CV). The resultsdemonstrate that the platinum nanowire arrays with a high-filling rate anda large area are dense, continuous, and keenness. Energy dispersivespectrometer(EDS) analysis indicates the platinum atomic. The resultingelectrode exhibits high elecrocatalytic activity towards the oxidation ofmethanol(CH3OH) and methanoic acid(HCOOH), the reduction ofhydrogen peroxide (H2O2).4. Ultralow Pt-loading Bimetallic Nanoflowers: Fabrication and SensingUltralow Pt-loading Au nanoflowers(AuNFs) were synthesized on aglassy carbon electrodesurface by the underpotential deposition(UPD)monolayer redox replacement technique, which involves redoxreplacement of a copper UPD monolayer by PtCl2-4that can be reducedand deposited simultaneously. Field-emission scanning electronmicros-copy, energy dispersivespectroscopy, x-ray photoelectron spectroscopy and the electrochemical method were utilized to characterize the ultralowPt-loading AuNFs. Cyclic voltammogram results showed that theultralow Pt-loading AuNFs exhibited excellent electrocatalytic activitytowards the reduction of hydrogen peroxide and the oxidation of glucosein neutral media, and the reaction path way of glucose oxidation waschanged from an intermediate process based on the electrosorption ofglucose to a direct oxidation process. From chronoamperometric results,it could be obtained that this prepared biosensor had wide linear rangesand very low detection limits(DLs) for H2O2(0.025-94.3uM; DL=0.006uM) and glucose (0.0028-8.0mM; DL=0.8uM), which were much betterthan previous results.