The Mechanism Study Of Surface Strain Affecting Electrochemical Properties Of Gold And Platinum Films

Recently,the coupling of surface mechanics and electrochemistry has been widely studied in the field of new energy materials.The catalytic activity of materials could be improved by means of strain effect.The traditional experimental method can obtain different strain state of surface atoms due to lattice mismatch.However,surface atomic monolayer is often subjected to electronic coupling with metal substrate(ligand effect).Thus,such traditional method cannot obtain the accurate relationship between strain and electrochemical processes.Based on the concept of surface mechanics,this paper employs mechanical methods of dynamic loading and bending deformation to separate the interference of ligand effect,and then investigates the accurate effects of dynamic strain and static strain under mechanical loading on electrochemical performance of metal electrodes.The physical mechanism is also explored.The research content mainly includes two parts:1)The gold(Au)surfaces were cyclically deformed by a periodical mechanical load in sinusoidal way,and then the response signals of capacitive current were in situ monitored.Since current response signal exhibited the same variation frequency as dynamic strain signal,the magnitude of current response to mechanical strain can be recorded by lock-in technique.This chapter investigates the dependence of currentstrain response on electrode potential,potential scan rate and strain frequencies.The interesting findings are: i)During charging and discharging processes,current response to strain is strongly dependent on the frequency of applied mechanical load and electrode potential,while it is weakly dependent on potential scan rate during cyclic voltammogram.ii)Tensile strain can enhance the capacitive current during charging process whereas tensile strain inhibits the current during discharging process.iii)The mathematical expression of strain effect on capacitive current is obtained based on a self-established equivalent circuit model of the double layer process which considers mechanical strain term.The results in this chapter conclude that electrochemical charge/discharge rate can be adjusted by mechanical methods,which further optimizes the electrochemical charging/discharging process and promotes the application of mechanics in the field of electrochemical energy storage.2)When the strain frequency approaches to zero,the strain could significantly affect surface charge.Thus,we further study the effect of static strain on electrochemical performance of metal electrodes.In this chapter,based on the thermal deformation characteristics of polymer substrates,we formulated a scheme for mechanical bending deformation to obtain different deformation states of surfaces.The XRD results show that the static strain of metal layers can reach 1%.Using simple method of cyclic voltammetry,we preliminary studied the effect of mechanical bending strain on the oxygen electrosorption.The experimental results show that the oxygen desorption peak potential on Au surface is positively linear with strain,whereas the oxygen desorption peak potential on platinum(Pt)surface is negatively linear with strain.Tensile strain contributes to oxygen desorption on Au surface,while compressive strain favors oxygen desorption on Pt surface.The research results in this chapter are consistent with the reported data in previous literature,confirming the correctness of the experimental methods in this chapter.The mechanical loading method explored in this chapter can be used as a simple strategy to modulate the electrosorption process on metal surfaces.