Preparation And Application Of All-solid-state Reference Electrode Based On Fast Ion Conductor

In the 21st century,the significance of ocean to human survival and development has become more and more obvious.Whether it is seabed metal deposits or energy and biological resources,because of its considerable reserves,it has been attracting the attention of countries all over the world since the last century.However,the complex and changeable marine environment has brought huge challenges to marine research.In order to realize the development and detection of the ocean,the development of robust and durable in-situ electrochemical sensors is an urgent problem to be overcome.With the continuous emergence of new indicator electrodes,marine electrochemical sensors have achieved unprecedented development,but their application scenarios and scope of use are still greatly limited by the lack of suitable reference electrodes.In the electrochemical system,the reference electrode has the same important role as the indicator electrode and is an indispensable key component.For this reason,it is of great practical significance to develop a marine reference electrode with corrosion resistance,high voltage resistance,ion interference resistance,and stable working performance.In this paper,three types of fast ion conductor materials:lithium molybdate tungstate（LWM）,NASICON and metal-doped NASICON have been designed and synthesized.And three types of new all-solid-state reference electrodes were prepared using the above-mentioned materials as the matrix.The higher ionic conductivity of the all-solid-state reference electrode material ensures the electrode’s rapid potential response in the electrochemical system.Good reversibility and chemical stability show the huge application potential of the reference electrode in the marine environment.The main research contents of this paper are as follows:（1）The reaction sintering process is used to synthesize a new type of lithium molybdotungstate（LWM）fast ion conductor in one step.SEM,XRD,XPS,complex impedance spectroscopy were used to systematically analyze the structure and performance of the fast ion conductor to explore the influence of lithium ion content on the structure and electrical properties of the material.Then the LWM all-solid-state reference electrode was designed and prepared with this material,and the potential stability of the solid-state reference electrode under different p H conditions and the cyclic voltammetry curve in potassium ferricyanide solution were tested to verify the reversibility and repeatability of redox.The above electrochemical tests have verified the reliability and stability of the LWM reference electrode.Then a p H sensor is formed with an iridium oxide p H electrode to test the response and stability for the p H value to verify the application prospect of the LWM reference electrode in electrochemical detection.At the same time,the mechanism of the all-solid reference electrode is discussed preliminarily on the basis of structural analysis.（2）High-temperature solid-phase method was used to synthesize NASICON fast ion conductor material with high conductivity and high density.Based on this material,the NASICON all-solid-state reference electrode is designed.In order to understand the influence of the conditions of the hydrothermal vent,we processed the NASICON fast ion conductor under the supercritical conditions of 400℃and 40MPa,and studied the changes in the structure and microstructure before and after the treatment.Then the characteristics and stability of the reference electrode before and after the supercritical treatment in water buffer solutions of different p H values were studied,and the impedance and I-V curves were tested and compared to analyzing the stability and repeatability of the redox reaction before and after the supercritical treatment of the reference electrode.The results show that after supercritical treatment,the reference electrode has good potential stability and redox reaction reversibility and repeatability.At the same time,the potential stability of the reference electrode under extreme conditions such as high temperature（400°C）,high pressure（60MPa）,high sulfur（0.1mol/l Na₂S solution）,and high salt（saturated potassium chloride solution）were also investigated.Then,the NASICON reference electrode is combined with the Ir/Ir O₂working electrode to make an all-solid-state p H sensor for measuring the p H value of simulated seawater.Finally,the mechanism of the reference electrode is discussed in conjunction with structural analysis.The above results verify that in combination with other sensing electrodes,the all-solid-state reference electrode can be used for analysis in harsh environments such as deep sea and high temperature and high pressure.（3）The Na⁺and Zr⁴⁺in NASICON are replaced by Li⁺and Zn²⁺doping respectively,and high-temperature solid-phase method was used to synthesize a doped and substituted NASICON-type fast ion conductor.The influence of doping on the structure and performance of NASICON fast ion conductor is analyzed.Then the corresponding all-solid-state reference electrode was prepared based on the Li⁺,Zn²⁺-doped NASICON fast ion conductor design,and the potential stability of these two all-solid-state reference electrodes under different p H conditions and potassium ferricyanide solution were also tested to verify the reversibility and repeatability of redox.The above electrochemical tests have verified the reliability and stability of these two doped NASICON all-solid-state reference electrodes.Then the p H sensor is also formed with the iridium oxide p H electrode to test the response and stability for the p H value to verify the application prospect of the reference electrode in electrochemical detection.