Effect Of Particle Size On Electrochemical Properties Of Blocky Nano-Electrodes

The electrode (galvanic cell) fabricated using nano-materials has excellent electrochemical performance, the discharge capacity increased, the electrochemical activity enhanced and the cycling stability improved. The electrochemical performance of cell depend on the electrochemical properties of the electrodes, however, at present the effects of size of electrode materials on electrochemical properties of the electrode have not been researched completely in theory, and the experimental research on regularity of effect of the particle size on the electrochemical properties of nano-electrode has not been reported yet. In the present paper, the relations between the electrochemical properties, such as electrode potential, electrode temperature coefficient and thermodynamic functions of electrode reaction, respectively, and particle size will be derived in theory firstly; then, the electrochemical properties of nano-silver oxide electrode and nano-silver electrode will be researched in experiment.In theory, the expression to describe the size-dependent electrode potential was derived according to the relation between molar reaction Gibbs function and electrode potential by introducing the interface variable in the molar Gibbs function of electrode reaction; then, the relations between the electrode temperature coefficient, the thermodynamic functions of electrode reaction, respectively, and the particle size were derived, the regularities of the electrochemical properties varying with particle size were discussed when the nanoparticles act as reactant and product for the electrode reaction.In experiment, nano-silver oxide electrode and nano-silver electrode were selected as research systems. Firstly, nano-materials for the electrode were prepared: using silver nitrate as raw material, potassium hydroxide as precipitating agent, nano-silver oxide was prepared by organic polymer dispersing method; and using silver nitrate as raw material, hydrogen peroxide as reducing agent, nano-silver was prepared by chemical reduction. The nanoparticles with different sizes were prepared by controlling the reaction condition, such as, reaction temperature, concentration of reactants, adding order. Secondly, the average size, the crystal structure, the purity and the shape of the prepared nanoparticles were characterized by XRD, EDS, TG/DTG and TEM. Finally, the blocky nano-electrodes were fabricated using the nanoparticles, and the electrode potential was determined by compensation method. The regularities of effects of size on the electrode potentials of nano-electrodes were obtained by determining the electrode potentials of blocky nano-electrodes with different particle sizes; the react sequence of nanoparticles with different particle sizes in electrode reaction process was studied by determining the electrode potential of blocky nano-electrode fabricated using different particle sizes. The electrode potentials of blocky nano-silver oxide electrodes with different sizes were determined at different temperature, and the electrode temperature coefficients of the nano-electrodes were obtained by fitting the data of electrode potential and temperature, consequently, the regularity of effect of size on the electrode temperature coefficient was obtained. The thermodynamic functions of electrode reaction were calculated according to the relations between the thermodynamic functions and the electrode potential or the electrode temperature coefficient. The experimental results were consistent with the theoretical research about the effect of size on the electrochemical properties of blocky nano-electrode. In addition, cyclic voltammetry curves of nano-silver oxide electrodes were measured at different scanning rates, and the kinetics of electrode reaction was preliminarily discussed.Some conclusions have been drawn from the theoretical research and the experimental results.(1) Using the organic polymer dispersing method, nano-Ag2O with average particle size range from12nm to60nm can be prepared; using the chemical reduction method, nano-Ag with average particle size range from26nm to58nm can be prepared; the reaction conditions have obvious effects on the particle size:the sizes of nano-Ag2O and nano-Ag increase with the reaction temperature increasing and with the concentration of silver nitrate increasing, in addition, the adding method has an effect on the particle size, the nano-Ag2O prepared by adding the silver nitrate solution into the solution of sodium hydroxide has smaller particle size.(2) There are obvious effects of the particle size on the electrode potential, the electrode temperature coefficient and the thermodynamic functions of electrode reaction. When the nanoparticles act as reactant of electrode reaction (such as Ag2O), with the particle size decreasing, the electrode potential and]nKe increases, the electrode temperature coefficient,△Hmθ,△Gmθ and△Smθ decreases; on the contrary, when the nanoparticles act as product of electrode reaction (such as Ag), the regularity about the particle size effects the electrochemical properties is just contrary to the former. The electrode potential, the electrode temperature coefficient and the thermodynamic functions have a linear relationship with reciprocal of the particle size, respectively.(3) Particle size has a significant effect on the react sequence of nanoparticles, the smaller nanoparticles preferentially occur electrode reaction; the electrode potential of blocky nano-electrode fabricated using mixture of nano-Ag2O particles with different sizes gradually decreases.(4) There is also an obvious effect of the particle size on the kinetics of electrode process, the controlling step of the electrode reaction process translates from the step of reaction to diffusion when the particle size of nano-Ag2O particles is nanocrystallized; and the reversibility of the electrode reaction decreases with the particle size decreasing.