Preparation,Characterization And Electrochemical Performance Of Polyaniline/pt Microelectrodes

Polyaniline has been widely studied due to its high conductivity, excellent electrochromic property, good redox reversibility and stability which have close relationship with the redox mechanisms of polyaniline. The nanosized Pt particles are widely used to electroanalytical oxidate small organic molecules according to the excellent catalytic performance.This paper focuses on preparation and electrochemical performance of polyaniline/pt microelectrodes. The redox mechanism of polyaniline, preparation of composite modified electrode and the electrochemical oxidation mechanism of formaldehyde were carried out by electrochemical and in situ rapid-scan time-resolved IR spectroelectrochemistry methods. The main results are as following:1、The electrochemical oxidation mechanism of polyanilineThe PANI films were grown electrochemically from solutions containing1.0M HC104and0.1M aniline by cycling the potential from-0.4to0.8V at a scan rate of lOmV/s. Polymer growth was terminated after15complete voltammetric cycles. The film thickness was estimated using the charge associated with proton doping of PANI. Based on our measurements the films are estimated to be approximately0.99μm thick. The redox mechamm of PANI was studied by in situ rapid-scan time-resolved IR spectroelectrochemistry (RS-TR-FTIRS) method. In the potential rang between-0.4to0.8V at a scan rate of5mV/s, there were four groups of redox peaks. The results illustrated that the first pair of redox peaks are according to oxidation of the secondary amines in the middle of molecular PANI chain, the second pair of redox peaks are according to oxidation of terminal primary amines, the third pair of redox peaks are according to oxidation of terminal hydroxyl groups, the forth pair of redox peaks are according to oxidation of the polaronic PANI to the bipolaronic PANI. The bipolaronic PANI completely turns to quinoid structure with highly conjugated by deprotonation, the steamed bun bands centered near3000cm-1disappeared when the potential was higher than0.71V.The reactions of the first group were those: Simultaneously, we calculated the two structural unit FTIR spectra of neutral molecule and cation molecule in PANI. The calculations show that the vN-H exhibit blue shift and greatly enhanced when the neutral molecules turned into positively charged molecules, which was in good agreement with in situ rapid-scan time-resolved IR spectroelectrochemistry experimental results. Experimental results at different temperatures indicated that the vN-H of radical cation exhibit blue shift from3875cm-1to4367cm-1and the peak intensity increases when the experimental temperature decreased from25℃to5℃.2、Preparation of polyaniline/pt microelectrodesIntroduction Pt in PANI membranes of polyaniline/platinum composites have primarily focused on exploiting the catalytic activity of the metals and the high conductivity of the PANI. The Pt particles were electrodeposited on the0.99μm thick PANI films with Pt load values of453μg/cm2. The SEM and TEM image illustrated that the PANI film is composed of100-200nm diameter rods and Pt particle was about300-600nm in diameter on the end of PANI membranes. HRTEM investigation indicated that the lattice fringes with a spacing of0.23nm were clearly visible in these nanograins and the diffraction peaks of XRD patterns at the29of39.9°correspond to the (111) facet of the face-centered cubic structures of platinum crystal, which is in good agreement with the standard card of cubic Pt (JCPDS No.4-802). The Infrared spectroscopy, Raman spectra and fluorescence spectra indicated that the benzenoid groups decreased and the quinoid groups increased when the Pt particles were electrodeposited on the PANI films. The peak potential separation in a solution of5m mol/L K3[Fe(CN)6]/K4[Fe(CN)6](1:1),(ΔEp) of0.082V, was observed corresponding to a reversible electron transfer process.3、Studying on the electrocatalytic oxidation of formaldehyde and methanolThe electrochemical oxidation of small organic molecules as a subject of long-term interest in development of fuel cell technology has been widely studied and continues to be of interest. However, few investigations investigated the electrochemical oxidation mechanism of formaldehyde as a model in alkaline solution. Firstly, the oxidation of formaldehyde in alkaline solution was studied by in situ rapid-scan time-resolved IR spectroelectrochemistry (RS-TR-FTIRS) method.In the potential rang between-0.7and0.2V, three bands at1588,1357cm-1(which could be assigned to the asymmetric and symmetric υoco of formate ions),1380cm-1(which could be assigned to the deformation vibration δC-H of formate ions) appeared and two bands at2765(which could be assigned to the υH-O of gem-diol anion),1034cm-1(which could be assigned to the υCO of gem-diol anion) decreased in aqueous solution. It was also conformed that four bands at1595,1357,1380,3427cm-1(which could be assigned to the υH-O of water) appeared and two bands at2026(which could be assigned t to the of gem-diol anion),1034cm-1decreased in heavy water solution. The results illustrated that formaldehyde formed gem-diol anion in alkaline solution and was absorbed on the electrode surface; then gem-diol anion was oxidized to formate ions and water; the mechanism is that: The overall reaction can be written as:Then the formaldehyde and methanol electrochemical oxidation on polyaniline/Pt microelectrodes were investigated. Electrochemical experiments show that polyaniline/platinurn microelectrodes have superior catalytic performance toward formaldehyde and methanol electrochemical oxidation. The chronoamperometric curves indicated high electrocatalytic stability catalyst for the formaldehyde and methanol oxidation. The polyaniline/Pt microelectrodes displayed excellent electrochemical catalytic activities with increasing of peak currents towards ascorbic acid (AA) and dopamine (DA) compared with bare GCE, Pt by differential pulse voltammetry (DPV). The limits of detection (S/N=3) for AA and DA were0.18mM and3.94μM, respectively. The linear ranges for AA and DA are0.25-3.0mM and10-200μM, respectively. Electrochemical experiments show that the polyaniline/platinum microelectrodes could be applied to chemical sensors, biosensors and fuel cells fields.