Effect Of Sulfate Adsorption On The Electrocatalytic Oxidation Dynamics Of Sodium Sulfide On The Polycrystalline Platinum Electrode

The adsorption of sulfate on the platinum electrode processes complex spatiotemporal dynamic behaviors in the electro-catalytic oxidation of sodium sulfide.By using the electrochemical cyclic voltammetry and a synchronous CCD camera,the N-shaped negative differential resistance?N-NDR?process of the sodium sulfide system is inhibited or promoted by the adsorption of sulfate ions under different conditions.Meanwhile,the change of pulse width and wave velocity varies with sulfate concentrations are observed under the potentiostatic control method.First,platinum oxide,as a highly active catalyst,is one of the most important intermediates in the electrocatalytic oxidation of sodium sulfide,whose research helps explain the mechanism of electrochemical oxidation of sodium sulfide.The results show that:?1?the increase of the scanning potential promotes the formation of high-valence Pt oxides such as PtOOH and PtO₂ as well as the evolution of oxygen.Meanwhile,platinum sites released by oxygen formation can be reabsorbed by the hydrogen oxygen and sulfate.2)Increasing alkaline of solutions contributes to the formation of platinum oxides.The potential of Pt oxides generation shifts negatively,and the oxidation peak current density increases with the increase of pH.?3?Keeping a constant pH of solutions,the increasing of sulfate concentrations shifts overall cyclic voltammogram curves to higher potentials,and also increases the oxidation peak current.?4?The external resistances in series with the working electrode reduce the Faraday current and inhibits the oxygen evolution reaction,which shift oxidation peak potentials negatively and decrease the current density.?5?Increasing current densities are observed with the scanning speed,and at the same time the generation of low-valence platinum oxide is promoted during the reverse scanning,however the peak potential remains unchanged.Furthermore,the low scanning speed promotes the evolution of oxygen.Secondly,the effects of adsorption of sulfate ions on Pt on spatiotemporal dynamics of sodium sulfide electrocatalytic oxidation are investigated under the conditions of 0?and 100?external resistances in series with the WE,respectively.When the series resistance on WE is 0,the N-NDR oscillations in both positive and reverse sweep are suppressed with the increase of sulfate concentrations.For the influence of the temporal spatial patterns,the sulfate ion converts the electrodesurface measured at 1.8 V by cyclic voltammetry from the local pulse to the synchronous sulfur deposition and dissolution.With the increase of sulfate concentrations,the pulse widths detected at 1.75 V by the potentiostatic method become narrower,while the wave velocity increases.When the sulfate concentration continues to increase,the adsorption of sulfate on the platinum electrode tends to be saturated,which leads to slowly decrease and rise of the wave width of the pulse wave.When the external resistance of 100?is in series with the WE,the chemisorption of sulfate on Pt leads to the positive shift of the onset potentials of both Pt oxides and oscillations at low potential.At high potentials,new HN-NDR oscillations are introduced into the transpassive potential region.From the sulfur deposition patterns,it is clear that the introduction of sulfate promotes the electrocatalytic oxidation of sulfide and suppresses the formation of bubbles at high potentials.Meanwhile,under the potentiostatic method control,increasing sulfate ions makes the mode of current density oscillation change from simple oscillation mode to complex oscillation mode,and finally evolves into coexistence of oscillations and noise.When the series resistance is applied,we also observe that the width of the pulse wave decreases with the increasing sulfate concentrations.Finally,the effect of sulfate adsorption on the formation of platinum oxide is simulated in a sodium hydroxide solution with a pH value similar to that of 1.0mol L^-1 sodium sulfide solution.The presence of sulfate ions causes the negative shift of the potential of platinum oxide formation and increases the current density of the oxidation peak,and shift the oxygen evolution potential positively by 0.4 V.It is proved that the adsorption of sulfate in sodium sulfide solutions promotes theconversion of sulfide,and inhibits the formation of oxygen.The simulated results are consistent with the experiment and as a result it proves the rationality of the sulfate adsorption mechanism.