Preparation Of The Heating Stage And Sample Cell Used For In-situ Raman Spectroscopy Of Electrochemistry Of Molten Fluoride System

In situ Raman spectroelectrochemistry is a method which can provide the information changes of ionic groups on and near the electrode surface.This method is an important way of investigation on electrochemical process,and usually used for study on the mechanism of electrochemical reactions.However,the corrosivity and volatility of molten salt limit the application of in situ Raman spectroelectrochemistry on molten salt,as well as the required focal distance of microscope.Based on the above mentioned reasons,this study aims on the investigation on the in situ Raman spectroelectrochemistry of volatile high temperature molten salts,especially on fluoride molten salts.Combining with the High Temperature Raman Spectroscopy Research Platform(HTRSRP)in Northeastern University(NEU),a heating stage and sample cell of in situ Raman spectroelectrochemistry was designed and improved to achieve the above mentioned aims,and measured the functions of the heating stage and sample cell.Silicon carbide rods were used as calandria,which could ensure a high-efficiency heating power;the electrode wires were inserted from the sidepiece of sample cell,in order to provide enough space for the Raman measurements;and the sample cell was closed using high-temperature cement,which could avoid volatilization of the melts.Moreover,a thermocouple was inserted from the bottom of the sample cell to ensure an accurate temperature measurement.The test results of the heating stage show that the heating stage can heat to 1029 ℃,and keep a homogeneous temperature distribution;meanwhile,the temperature around the window of heating stage can keep at around 300 ℃,which means the measurement can be carried out using a micro lens with focal distance of 1.5 cm.The in situ Raman spectroelectrochemistry was measured in KF-KBF4 molten salt system using the designed heating stage,and Raman spectra with high noise-signal ratio were obtained.The results indicate that the equipment can be used for highly-accuracy measurements of in situ Raman spectroelectrochemistry in molten salt at high temperature.According to the measurements,it can be concluded that[B3+]and K+ are reduced at the potentials of-1.0 and 2.0 V vs.Pt,respectively.In addition,the electrochemical measurements were carried out in NaF-AlF3-Al2O3-KF molten salt systems with various KF content.The results indicate that aluminum-fluorine complex anion discharges at the potential of －0.6 V vs.Pt;during the forward scan,metallic aluminum is oxidized,firstly,then Pt working electrode begins to be oxidized when the scan potential exceeds 1.0 V.It is suggested that an excellent experimental result can be obtained using a working electrode with size of 2×3mm and under a potential scan rate with 0.1 V/s.However,during the coupling experiments of electrochemical measurements and Raman spectroscopy in NaF-AlF3-Al2O3-KF molten salt,high-precision experiments and analysis cannot be treated because of low noise-signal ratio of the obtained spectra resulted from the low laser power and powerful black-body radiation of heating stage.At last,a development of the experimental equipment is proposed.The significance of this work is laying a groundwork for the development of the High Temperature Raman Spectroscopy Research Platform(HTRSRP)in Northeastern University(NEU).