Study On The Size Effect Of Ionic Solvation In The Formation Of Electric Double Layers

The electric double layer is a very important component in the study of interface chemistry.The electric double layer structure in the interface chemistry plays a very important role in the electrode process dynamics.It is a very common phenomenon that the electric double layer appears on the solid-liquid interface.The interface chemistry of the theory of electric double layer structure is also the intermediate link between the electrochemistry thermodynamics and the electrode process dynamics.In summary,it is necessary to study the formation process of double layer structure for electrochemical processes,such as electrochemical energy storage,electrocatalysis,electrical separation and electrical sensing.Electrochemical quartz crystal microbalance(EQCM)combined with cyclic voltammetry is a very effective in-situ monitoring technology.It can obtain the quality information of the electrode surface at the same time as the electrochemical test parameters.Combined with Faraday’s law,it can quantitatively describe the solvation number in the formation process of double-layer capacitance by quantitative analysis of the quality change information of the electrode surface.According to analysis the quality information quantitatively of the adsorption and desorption of solvated ions at the electrode surface,it can provide very effective information for further study of electrode reaction mechanism.In this work,electrochemical quartz crystal microbalance(EQCM)technique was used to characterize the two kinds of activated carbon materials with different pore sizes in five different electrolyte solutions,including three influencing factors:anti ion size,solvent molecular polarity and ion concentration at room temperature.Through quantitative calculation and analysis,the apparent molecular mass(Msx)was calculated from the slope of the electrode mass change(△m)vs.the charge(△Q)passed in the electrode during charging/discharge.Then,compared Msx with the molar mass of bare ion,the value of specific solvation number(x)can be obtained.It was found that formation of double layers at electrode interface by ionic absorption was accompanied with solvation effect.The solvation effect was weakened as the pore size of electrode decreased,concluded as pore size effect existing concurrently with solvation effect during ionic adsorption.The pore size effect was influenced by the size of counter ions,polarity of solvent molecules and ionic concentrations.The larger the size of the counter ion is,the size effect plays a more important role in the formation of the double layer.The larger dipole moment of the solvent molecule causes the stronger the pore size effect on the Li+solvation during adsorption.The force of ion dipole bond formed is also larger,making the pore size effect on the corresponding solvated cations stronger.In a concentrated solution,the pore size effect on Li+solvation was enhanced in a concentrated electrolyte.The solvated number x was also affected by the size of anion,polarity of solvent molecules and ionic concentrations.