Research Of An Ag/AgCl Reference Electrode For High-Temperature/High-Pressure Environment

In this study, AgCl powder with fine particle size was synthesized and used for the preparation of Ag/AgCl electrode. The influence of different powder forming technology and particle's diameter on electrode performance was investigated by the electrochemical measurements and microstructure observation. Ag/AgCl electrode was applied to high temperature high pressure electrochemical measurement by a self-designed external electrode device. Meanwhile, the temperature field in the main body of the external electrode device is simulated with the aid of computer software COMSOL, the temperature profile of the reference electrode structure were obtained. Using this profile and available thermodynamic data, the possible potential errors was estimated. The Cu/Cu2+ half-cell was used to validate the calculations.AgCl powder with fine particle size was prepared by using liquid precipitation method and room-temperature solid-phase synthesis method. The laser granulometric analysis and scanning electron microscopy was used to characterize the par-ticle size. The result shows that the AgCl powder prepared by liquid precipitation method has a finer particle size, but the AgCl crystals grew up obviously during the separation process, the mean particle size increased from 77.2 nm to 4 ?m. However, by using room-temperature solid-phase synthesis method, the AgCl grain growth is not obvious in the process of separation and dryness, with the mean particle size of 574.6 nm.The blended powder of Ag and AgCl was molded by direct compression method,powder-sintering method and hot-press sintering method.The electrochemical measurements and microstructure observation was used to characterize the electrodes' performance. Results show that,using submicron Ag powder and submicron AgCl powder as raw materials,Ag/AgCl electrode prepared by hot-press sintering under the condition of 400? has the best stability, accuracy and reversibility. It's potential response to the change of Cl- concentration and temperature is sensitive, the polarization resistance of the Ag/AgCl electrode Rp=11.54?·cm2,which means this Ag/AgCl electrode has a very good resistance of polarization.Ag/AgCl electrode was applied to high temperature high pressure electrochemical measurement by using a self-designed external electrode device. Subsequently, heat transfer analysis of the electrode structure was carried out and the physical model for the heat pipe exchanger was established. Using the temperature profiles and available datas, the potential errors at the initial temperature of 373 K was calculated. The thermal liquid junction ETLJP?2.9 mV. The isothermal liquid junction EILJP 0.15 mV. The calculations for IR drop and porous ceramics ohm drop were also performed. The resistance of the solution in electrode pipe Rs=362.93 ?, the resistance of porous ceramics Rpc = 19.9 ?. The theoretical potential,along with other irreversible potential components, were validated with Cu/Cu2+ potential measurements under the condition of 100?, 20 MPa. A good agreement is found between the theoretical potential and experimental observations with an error of 3 mV.