Study On The Preparation And Failure Mechanism Of Ti/BDD Coated Electrode

Boron doped diamond(BDD)electrode with wide potential window,high oxygen evolution potential,low background current,high physical and chemical stability is an ideal electrode material.Ti/BDD coated electrode combines the comprehensive advantages of Ti and BDD materials and has a good prospect in industrial application.However,the short service life of Ti/BDD coated electrode limits its practical application.So far,there are still disputes on the failure mechanism and influencing factors of Ti/BDD coated electrode.There is no good solution for how to effectively prolong the service life of Ti/BDD coated electrode.In this paper,the research on the prepararion of Ti/BDD coated electrode by high current extended direct current arc plasma CVD(HCDCA-CVD)method was conducted.The effects of process parameters on the structure and properties of electrodes were systematically studied.The growth kinetics of BDD coating on the Ti substrate was studied.The Ti/BDD coated electrode with good quality and electrochemical performance was successfully prepared by the two-step preparation process.The potential window and oxygen evolution potential of the Ti/BDD coated electrode in 0.5mol/1 H2SO4 solution are 3.51v and 2.42v respectively.When the chemical oxygen demand(COD)removal efficiency of the glucose solution with the initial COD value of 982mg/L reached 89.4%,the energy consumption value was 27.2kwh.m-3.The electrode structure and electrochemical properties are similar to those of BDD coated electrode samples prepared by hot filament chemical vapor deposition(HFCVD)and microwave plasma chemical vapor deposition(MPCVD)methods.By accelerating the life test(ALT),various analyses techniques were combined to track Ti/BDD electrode failure process.The results showed that during the ALT process,the failure process of the Ti/BDD electrodes may be divided into two stages.In the first stage,'defects existed in the coatings may lead to penetration of electrolyte into the BDD coatings,resulting in cracking and delamination of the coatings.Then in the second stage,corrosion of BDD grains and dissolution of intermediate titanium carbide layers occur accompanied by slow coatings delamination.The failure process of Ti/BDD and Nb/BDD electrodes was comparatively studied.The results showed that the main failure mechanism of the two types of electrodes was delamination of the BDD coatings,accompanied by coatings'corrosion.The delamination of BDD coatings from both the substrates all showed an incubation period,with the Ti/BDD electrode having a much shorter incubation period and a higher coating delamination rate than its counterpart.By comparing growth process of diamond coatings and corrosion behavior of carbides formed on both types of substrates,it was found that on Ti substrates,diamond coating was more liable to incorporate pore defects,and carbide layer formed beneath the diamond coating was more susceptible to corrosion in electrolysis solution.It is believed that these two factors would lead to a shorter service life for Ti/BDD electrodes than that for Nb/BDD electrodes.The effects of process parameters on the BDD coating structure and corrosion resistance of Ti/BDD coated electrode were studied.The results showed that the electrode life increased first and then decreased with the increase of the flow rate of CH4 during nucleation stage and the flow rate of B source during deposition.Combined with the optimization of process in different stages,the gradient boron doping method was adopted to improve the corrosion resistance of BDD coating and reduce the structural defects of BDD coating.On the basis of the original preparation process,the ALT life of Ti/BDD coated electrode was significantly improved.The electrode life was increased from 147h and 360h to 196h and 655h under the constant current density with 1A/cm2 and 0.5A/cm2,respectively,and with an increase of 33%and 82%,respectively.