Underpotential Deposition Behavior And Dynamic Process Of Copper On Polycrystalline Platinum And Gold Electrodes

Underpotential deposition(UPD)is a special electrodeposition phenomena which is a kind of metal ion can deposited on another matrix with more positive potential than thermodynamic equilibrium potential.Since the composition and properties of the deposit film were extremely sensitive to various parameters such as electrode/solution interface and the composition of electrolyte.so it is significant to study the UPD behavior and mechanism of metal ion under different conditions(the electrolyte composition,anion adsorption capacity,electrochemical parameters,etc.).In this paper,the cyclic voltammetry(CV),chronoamperometry(CHR)and electrochemical impedance spectroscopy(EIS)techniques were in conjunction to investigate the UPD behavior of Cu ion on Polycrystalline(Pc)Ptand Polycrystalline(Pc)Au in different parameter conditions and anion systems.Meanwhile,the effects of different electrochemical parameters on the electrode surface kinetics were also be systematic studied.The main results are as follows.(1)CV measurements showed that Cu has different electrochemical characteristics on Pc Pt and Pc Au in the four systems of sulfuric acid,perchloric acid and Cl-were added respectively,there are both a wide potential range,more complex peak types and more pairs ofdeposition/dissolution peaks,which can be considered as a surface-limited electrodeposition process.It can be judged that the work function of heterogeneous phase between metal matrix and deposition particles is the dominant basis for the occurrence degree of UPD because the peak position and width of UPD body are not significantly affected with the copper ion concentration increases.At the same time,the Cu UPD behavior on Pc Pt and Pc Au shows different voltampere behavior characteristics under different anion conditions,mainly reflected in different deposition and dissolution peaks,different potential ranges and different peak types.(2)According to the analysis ofCu UPD process on Pc Ptand Pc Au,we can come to the conclusion from above four acid systems that the diffusion impedance of Cu UPD on Pc Pt is 0.2VSCE,and the impedance modulus decreases due to the negative shift of potential,there are always two phase Angle and which moves to the higher frequency region with the negative shift of potential,when it comes to Cu UPD on Pc Au,the diffusion impedance appears at 0.3VSCE and the phase Angle peak changes from one to two and also moves towards the high frequency region due to the negative shift of potential according to the Bode diagram.(3)Based on the above results,the four acid systems were following the Langmuir-type adsorption/desorption process and two-dimensional instantaneous nucleation(Q2Di-Li)and two-dimensional continuous nucleation(Q2Sp-Li),but anions have significant influence on Cu UPD process follows the order of juPD(SO42-+Cl-)>juPD(ClO4-+Cl-)>jUPD(SO42-)>jUPD(ClO4-).From Cu UPD on Pc Pt,because of the coverage degree of adsorption atoms,the proportion of charge density in the adsorption process(qad)decreases along with potential negative shift in sulfuric acid system,while when potential negative shift in perchloric acid system,the qad increases first then decreases,which means Cu UPD adatom coverage is unsaturated,but similar to the sulfuric acid system,the two-dimensional instantaneous nucleation(Q2Di-Li)is always greater than the two-dimensional continuous nucleation(Q2Dp-Li),indicating that Q2Di-Li is the main process of Cu UPD.Compared with Cu UPD on Pc Pt,Cu UPD on Pc Au process as a smaller charge density and shorter adsorption/growth process,it shows that Cu UPD on Pc Au is weaker than Cu UPD on Pc Pt,and Q2Di-Li is still greater than Q2Dp-Li.Moreover,with the potential shift towards negative,the charge density in the nucleation growth process increases continuously,indicating that the negative shift of potential is in favor of Cu UPD process.