In Situ Raman Spectroscopy Of Surface Species On Metal Electrodes In The Process Of Electro-oxidation Of Sodium Sulfide

In this paper,in-situ Raman spectroscopy was used to detect the intermediates during the electrocatalytic oxidation of sodium sulfide on the platinum and gold electrodes surfaces.The Raman peaks obtained by the microscopic confocal Raman spectroscopy technique were compared and analyzed,as well as the electrochemical behaviors during the reaction were make sure by the cyclic voltammetry and the potentiostatic method.The positions of Raman characteristic peaks of several reaction intermediates such as S8 poly sulfide and platinum oxide were determined,and process reaction mechanism and oscillation feedback process about the oxidation of sodium sulfide on platinum and gold electrodes surface was proposed.First,the steady-state electrochemical behaviors of sodium sulfide electrooxidation on platinum electrodes and the in-situ Raman spectra of the components detected during the reaction were discussed.There are six characteristic peaks in the Raman spectrum of sodium sulfide electrooxidation on the platinum electrode.150 cm-1,220 cm-1,470 cm-1,which is the vibration of S-S bond of polysulfide S8;190 cm-1 is designed to the vibration of Pt-0 bond,240 cm-1 is designed to the vibration of Pt-Ox bond,which belongs to the formation of platinum oxide;440 cm-1 is the vibration of Pt-S1 bond.In the steady-state system of sodium sulfide electrooxidation on the platinum electrode,the change of the sodium sulfide concentration will affect the position of the oxidation peak.When the sodium sulfide concentration is in the same order of magnitude,the oxidation peaks of the obtained cyclic voltammograms have similar positions and similar peak shapes.The concentration of sodium sulfide decreases,the oxidation peak shifts to the positive position,and the peak shape changes.As the sodium sulfide concentration increases,the position of the oxidation peak shifts to the negative and the peak shape also changes.This is because the sulfide ion concentration affects the electrocatalytic oxidation activity of the electrode surface.When the sulfide ion concentration is lower than the critical value,the surface of the electrode cannot regenerate enough active platinum vacancies to continue the catalytic oxidation cycle.Combined with the Raman spectroscopy,it can be seen that the Raman peak of the oxide appears after the sulfide,and the increase and decrease of the oxide's Raman peak correspond to the increase and decrease of the current in the positive sweep curve of the cyclic voltammetry respectively,and the appearance and disappearance of oxidation peaks in the cyclic voltammogram.At the termination of the reaction,a large amount of elemental sulfur deposition occurs on the surface of the electrode.The electrochemical oscillation of sodium sulfide at the platinum electrode is related to the reaction temperature,the shape and size of the reactor,and the concentration of the reactants.Oscillation cannot be produced in the in-situ pool under the conditions of the ordinary reaction cell for the reason of the size and shape connected to the pool.The conditions of oscillation in the in-situ reaction cell were obtained by changing the concentration of the reactants and applying the more external resistance.In the potentiostatic oscillation curve,the increase and decrease of the current correspond to the decrease and increase of the Raman peak intensity,and the peaks and troughs of the oscillation correspond to the highest and lowest Raman peak intensities,respectively.The position and number of Raman peaks in the steady state process of sodium sulfide electro-oxidation on the gold electrode are similar to those on the platinum electrode,and their attribution is also consistent with that on the platinum electrode.In addition,integrated the cyclic voltammograms and the Raman peaks of the reaction,it can be found that the oxidation peaks of the obtained cyclic voltammograms have similar positions and similar peak shapes when the sodium sulfide concentration is in the same order of magnitude,and the change law of the Raman peaks was consistent with the cyclic voltammogram.