Preparation And Properties Of Low Noise Composite Porous Ag/AgCl Electrode For Underwater Weak Electric-field Measurement

Underwater weak electric field detection technology can be widely used in marineresources survey, metal corrosion protection and detection in marine industrial and shipelectric field detection, etc. Marine electric field measurement devices consist of electricfield sensor (also called electrode) and digital information processing system, and theelectrodes with good properties play an important role in the electric field measurement.Ag/AgCl electrode is a reference electrode with good properties, and has a wideapplication in scientific experiments and engineering practice. This paper focuses on thepreparation of low noise composite porous Ag/AgCl electrodes, which can be used inweak electric field measurement. The relationship among preparation, structure andproperties of composite porous Ag/AgCl electrodes was investigated systematically.Meanwhile, the theoretical models of the porous Ag/AgCl electrodes were constructedcorrespondingly. The effect on and mechanism of the property of porous electrodepolarization and voltage noise were discussed. Furthermore, the relationship among thestability of electrode potential, the property of porous electrode polarization and voltagenoise was also discussed. The stability of the electrode was measured, and thesimulation test of the induction of the electrode under the applied electric field wascarried on.It is known that the poor short-term stability of electrode potential and highelectrode noise will greatly affect the sensitivity of electrode measurement. In addition,the properties of the electrode directly depend on the composition and structure of theelectrode. Thus the material preparation and structure control of electrode are studied inaspects of theory and experiments. The main works of this paper are as follows.Firstly, physical and chemical properties of precursor powders were researched andoptimized. Because the generation speed of AgCl powders is so fast that their particlesize distribution is not uniform easily. So several kinds of preparation methods werestudied and improved. Then the physical and chemical properties of AgCl powders werecharacterized correspondingly. The results showed that solid phase ball-milling methodwas superior to other methods. Superfine AgCl powders with particle size about1~2μm,which are narrow in particle size distribution, loose in structure and good in dispersion,were obtained by optimized solid ball grinding process.Secondly, the structure of the electrode was improved. The electrode moldingprocess was discussed by the microstructure analysis of the electrode. It is found thatthe porous structure of compound Ag/AgCl electrode, which was related to the process electrode.The theory model of porous electrode polarization properties was founded first.Then the rule of porous electrode polarization was experimentally validated. Accordingto the electrochemical reaction mechanism and the equivalent circuit of compositeporous Ag/AgCl electrode, the porous electrode polarization formulas were deduced.The steady state polarization curves of porous electrodes were also measured. Thevalues of exchange current density and polarization resistance depend on the structureof the electrode, which changed the electrode polarization performance and the stabilityof electrode potential.Additionally, the voltage noise properties of electrode were studied. The generatingmechanism of the voltage noise and its dependence on the electrode structure werediscussed by an analysis of electrochemical reaction process of the Ag/AgCl compositeporous electrode. Furthermore, all of these have been verified by experiments. It isfound that the increase of the effective porosity of the electrode and specific surfacearea can reduce the electrode voltage noise level, and the partial uneven polarization ofporous electrode would lead to higher voltage noise and lower stability of electrodepotential. This conclusion was in good coincident to the test result of electrodepolarization properties.In addition, various performance of Ag/AgCl porous electrode produced byoptimization process was analyzed. It is obtained that the exchange current density andvoltage noise density of the electrode are85.51mA·cm-2and1.74nV/√Hz（at1Hz),respectively. The stable average value of electric potential difference of two electrodeswithin24h is0.08mV, which fluctuated within0.028mV. After soaked in3.5%NaClsolution for76days, the electric potential difference between two electrodes remainedat about0.169mV, which fluctuated within0.030mV/24h. Compared with those ofother domestic products, these indicators exceed one order of magnitude. And especiallythe voltage noise density of the electrode reaches the international advanced level.Finally, based on the idea of virtual instrument, electric field measurement systemwas established under the applied simulation electric field, and the induction of theelectrode under the extremely low frequency electric field was measured and analyzed.In the measurement of sensitive frequency range, the electrode showed good frequencyresponse characteristic, which can meet the requirements of electric field detection inwater.