Study On Interfacial Electrochemistry Of Glassy Carbon And Its Effect On Carbon Supported Platinum Catalyst

Because single atom anchored at on a solid surface has the homogeneous and heterogeneous catalytic properties,single atom catalyst(SAC)has been the research frontier in the field of catalysis in recent years.And one of the most important research directions is to develop single metal atom catalyst at the carbon surface.Nevertheless,the preparation of the SAC/carbon is limited to the use of graphene as the support so far.Whether other sp2 hybrid carbon materials can be used to fabricate the SAC/carbon is an important issue worth exploring,in which there are two key unsaved scientific questions,including:(I)the key interface characteristics of sp2 hybrid carbon materials for the preparation of SAC/carbon;(2)the cause and control method of those key interface characteristics.in this thesis,to solve the above two key scientific problems,two most commonly used sp2 hybrid carbon materials,glass carbon(GCE)and graphite,were taken as the research objects.A voltammetric method was developed to regulate the GCE and graphite electrode interfaces in 0.5 M H2SO4 electrolyte.And the SAC/carbon was prepared by means of the adsorption-electrochemical reduction approach.The dispersion and electrocatalytic properties of two SAC/carbon electrodes were systematically characterize,while the surface/interface structure-activity relationship and the essential differences between GCE and graphite were studied.In chapter 3,firstly,the relationship between the onset reduction potential of platinum ions adsorbed on the surface of glassy carbon(CGCE)and the pH of the electrolyte was determined,while the changes in the valence states of the adsorbed platinum ions before and after electrochemical reduction were examined by XPS technique;subsequently,the electrocatalytic behaviors of SAC/CGCE for the formic acid(HCOOH),CO and reduced hydrogen evolution were investigated using electrochemistry and IR methods;finally,the adsorption sites of Pt ions on CGCE surface were studied by molecular probe method.The results showed that:(1)after soaking CGCE in 5 mM K2PtCl6 aqueous solution,the adsorption species on its surface was[Pt(OH)2]2+;(2)after the electrochemical reduction in NaAc/HAc(pH=4.50)solution at the hydrogen evolution potential(-0.2v vs SCE),Pt in the form of+2 valence was still highly dispersed on the CGCE surface,and had the extremely high electrocatalytic activity,like as the SAC reported in the literature(for example,the TOF of CO oxidation was about 0.13s-1);(3)on the CGCE surface,the adsorption and deposition sites of Pt are the basal planes of carbon microcrystals with electrical disturbance;(4)on the treated graphite electrode surface,Pt clusters would be obtained by the same adsorption-electrochemical reduction method.Furthermore,the key difference between the surfaces of the oxidized glass carbon and graphite is that the former generates a dense surface oxidation layer,which only contains highly dispersed carbon microcrystalline basal planes surrounded by surface oxygen-containing groups,thus the reduced Pt can maintain high dispersion.In contrast,the latter surface oxidation layer contains larger basal planes,along which Pt aggregates are likely to occur to form atomic clusters after reduction.In acidic electrolyte,a couple of reversible redox peaks are generated by electrochemical oxidation of glassy carbon electrodes.In chapter 4,the characteristics of this surface redox peak on CGCE and PGCE were investigated systematically.High vacuum heat treatment(HVT)was used to further regulate the surface,and XPS technology was combined to detect the difference of species on the surface when the electrode was in the states of reduction and oxidation.The relationship between electrochemical reaction kinetics of electrode surface and HVT temperature was studied by using vitamin C and Fe2+/3+ as electrochemical molecular probes.The experimental results revealed that the reversible redox peak was related to the oxygen-containing groups on the electrode surface,as well as the electrochemical conversion of sp2C and sp3C.HVT below 400? would deteriorate the surface kinetics of the electrode.Nevertheless,after higher than 600? HVT to remove most of the oxygen containing groups,resulting electrodes had similar dynamics properties as the initial CGCE and PGCE,revealing that the electrical dynamics properties of GCE surface mainly depends on its surface carbonyl group and electroactive sp2C/sp3C.The latter is closely related to the defected basal plane of carbon microcrystals.