Preparation Of Gold And Silver SERS Substrate And Its Application In The Study Of The Electrochemistry Process In Carbonate At High Temperature

Nowadays,fossil resources are burned in modern industrialized society,which leads to a large amount of carbon dioxide entering in atmosphere and causes serious greenhouse effect.However,the oxygen can be obtained at the anode by electrolyzing CO2 in carbonate system and carbon can be obtained at the cathode,which effectively reduces the emissions of CO2 and achieves its comprehensive utilization.Li2CO3-K2CO3 is one of the most widely used systems in that process.On the other hand,electrochemical in-situ Raman spectroscopy can provide information on changes of ion groups on the electrode surface,which is helpful to deeply understand the mechanism of the electrochemical reaction.The application of Surface Enhancement Raman Spectrum(SERS)overcomes the weakness of conventional Raman spectrum detection signal and makes it possible to find the weak Raman signal of intermediate substance,which is beneficial to the further application of electrochemical in-situ Raman spectroscopy in molten salt.Based on the above analysis,this present study has focused on the preparation of SERS substrates and characterization of their related properties,the electrochemical reaction process and mechanism in Li2CO3-K2CO3 molten salt system were explored by combining electrochemical in-situ Raman spectroscopy with SERS.Therefore,Au and Ag which display inert properties in the carbonate were chosen as research objects.The SERS substrate was prepared by oxidation reduction method and electrodeposition method,and Rhodamine 6G was used as molecular probe to research the enhanced effect,uniform stability and morphology.The experimental results have shown that the Au and Ag substrates prepared have strong enhancement effect and good homogeneity stability.Meanwhile,the SERS effect of the substrates obtained by the redox method is more obvious,and the stability is also stronger.The enhancement factor of Ag SERS substrate prepared by oxidation-reduction method is the largest,reaching at 1.37×104.Then,the enhancement performance of SERS substrate at high temperature has been investigated.The reason of the weakening of high temperature SERS effect is analyzed by the morphological changes of the substrate at different temperatures.It is believed that with the increase of temperature,the particles on the surface of the substrate were oxidated and became bigger and the roughness decreased,which led to the decrease of the SERS effect.But the three kinds of SERS substrates prepared still showed a certain surface enhancement effect after high temperature heating.At the temperature more than 600?,the enhancement factor of Au SERS substrate prepared by oxidation-reduction method was the highest value,reaching to 8.76 x 102.Subsequently,the electrochemical reaction process of Li2CO3-K2CO3 molten salt system was researched.It is believed that CO32-was reduced prior to metal cation and the reaction is CO32-+4e-=C+302-,and the carbon correspendently generated would react in the oxidation process and the reaction is C+202-=CO2+4e-.On the basis of the above studies,the smooth Au electrode and Au electrode with SERS effects were used as working electrode to explore the intermediate products generated during the electrochemical process in molten salt system,respectively.Electrochemical in-situ Surface-Enhanced Raman Spectroscopy experiments were carried out at-1.7V(vs.Pt-QRE)and-1.8V(vs.Pt-QRE)respectively under the condition of constant potential.Comparing the experimental results with the pure carbonate Raman spectra,a new peak can be found near the vicinity of 800cm-1 which is thought to be caused by peroxide ion(O22-).Therefore,the reduction of CO32-was assumed to be carried out by two continuous steps:2CO32-+2e-=2C+3O22-,O22-+2e-=202-.The prepared Au SERS substrate is proved to show some strengthening effect of Raman signal to complex and intermediate products in molten carbanates.