The Study Of The Electrochemical Properties For Graphene-metal Nanocomposites Electrode At Variable Temperatures

Graphene comprises a robust two-dimensional(one atom thick)honeycomb carbon sheet of sp2-hybridized carbon.It is a basic unit of the other carbon allotropes.As a kind of unique two-dimensional crystal,graphene exhibits remarkable properties.It can be used as ideal filler to prepare the high strength and conductive composites.Dispersed in a solution,graphene can be mixed with the polymer monomer to form composites.Therefore,in recent years,electrocatalytic properties of graphene and its applications in biological research has greatly attracted the attention of analytical chemists.As an important factor of the electrochemical reaction,temperature can greatly change mass transfer rate,electrochemical reaction rate,electrode potential of redox reaction and adsorption/desorption process of the species on the surface of electrode.For instance,electrocatalytic reaction plays a role in accelerating the charge:to transfer from the electrodes to the electrolyte interface.Good electrocatalyst has the characteristics of excellent activity,high stability and unparalleled conductivity.And it is widely used in fuel cells,solar cells and water splitting in the electrochemical reaction.Factors affecting the activity and stability of electrocatalyst include its microstructure and composition,reaction temperature,reaction pressure and mass transfer rate,etc.This thesis will develop and employ a new technique which is based on the thermocouple microelectrode and able to combine local temperature control/detect with electrochemical measurement.Also the technique is applied to investigate the field of electrochemical catalysis.We aim to make it become a kind of new methods for direct heating electrocatalys and in situ studying the dependence of electocatalyst on temperature.The main contents and result are listed as follows:1.The method for fabrication and characterization of rGO-Au compositesGraphene oxide(GO)was prepared by modified Hummers method.As-prepared GO along with chloroauric acid are used as precursors to fabricate the rGO(reducted Graphene oxide)-Au nanocomposites on the surface of the indium tin oxid(ITO)conducting glass by eletrochemical reduction method.The composites were characterized by cyclic voltammetry,Raman spectroscopy and atomic force microscopy(AFM)to study its electrochemical properties and morphology.2.The method for fabrication and characterization of thermocouple microelectrode which can be applied for heating electrocatalytic systemsIn order to establish a system which is based on the thermocouple microelectrode and able to combine local temperature control/detect with electrochemical measurement,we proposed a new method to pretreat the thermocouple microelectrode.Firsty,Pt and Pt-Rh wires are melt into a measuring junction using a hydroxygen flame.The as-melted spherical joint is acted as the measuring point.A thermocouple with a tip apex diameter of approximately 10?50 ?m can be fabricated by polishing process.Secondly,gold is electroless plated on the surface of the thermocouple microelecrode to shelter the high-activity of the Pt-Rh.In this way,the gold-plating thermocouple microelectrode become a local temperature-control/detect basal electrodes.Finally,the as-fabricated thermocouple microelectode is characterized by elecrochemical method and field emission scanning electron microscopy(FE-SEM)to study its electrochemical properties and morphology features.3.rGO-Au nanocomposites modified on the gold-plating thermocouple microelectrode and its activities of the oxygen reduction reaction(ORR)at variable temperatureBecause ORR is significant for dissolved oxygen sensors,biosensors,fuel cells,the metal corrosion and so on,it greatly attracts the interest of the researchers.The design and fabrication of highly active,durable and low-cost electrocatalysts for the ORR constitute a critical need toward the development of fuel cell devices for practical applications.Graphene supported gold nanoparticles have the capacity to enable enormous catalytic activity and can be studied for a kind of electrocatalysts for the ORR.rGO-Au nanocomposites are modified on the surface of gold-plating thermocouple microelectrode by using elecrochemical method.Utilizing the system equipped with the three functions including temperature control/detect and electrochemical measurement,we can investigate the influence of temperature to activities of the composite for ORR.