Study On The Preparation And Properties Of Membrane Electrode Assembly And Anode Catalysts In Electrochemical Bunsen Reaction

The demand for fossil fuels is increasing due to the development of industry.More than 80%of SO₂ released into the atmosphere by human activities comes from burning of sulfur containing fossil fuels,mainly coal and oil.As a highly toxic pollutant,SO₂has many harmful effects on environment and human beings.However,SO₂ is also a raw material for energy production,which can be produced hydrogen by electrolysis in the presence of water.The theoretical anodic overpotential of SO2 electro-oxidation is only 0.158 V vs.RHE,far lower than that of electrolytic water(1.23 V vs.RHE).Related applications include flue-gas treatment,hybrid sulfur(Hy S)cycle and thermochemical sulfur iodine(SI)cycle.Because of the advantages of low temperature and high efficiency,SI cycle has been studied extensively.As the first step of SI cycle,electrochemical Bunsen reaction plays an important role in the subsequent reaction.Although the reversible potential of SO₂ oxidation reaction is low in thermodynamics,the overpotential of the reaction is high due to the limitation of kinetics.Therefore,in order to expand the development prospects of SO₂ electrolytic cell,it is necessary to reduce the electrooxidation reaction impedance of SO₂.The current research focuses on the development of suitable anodic electrocatalysts to enhance the electrooxidation activity of SO₂.Pt catalyst has attracted the most attention because of its good electrochemical activity and stability.In order to reduce the voltage of electrochemical Bunsen reaction,commercial 60% Pt/C catalysts were selected to prepare the membrane electrode assembly(MEA)by spraying method.The effects of Nafion content and catalyst load in catalytic layer on the reaction were studied by various electrochemical measurements at room temperature.The results showed that with the increase of Nafion content(from 13%to64%),the cell voltage and energy consumption had the same trend of decreased first and then increased.When the Nafion content was about 37%,the cell voltage was the lowest,as well as the energy consumption.At this time,good transport channels of electron,proton and reactant were constructed in the catalytic layer.The MEA performance increased first and decreased afterwards with the catalyst load increasing(0.4-1.6 m A/cm²),and the best performance was achieved with the load of 1.2 mg/cm².When the current density was 50 m A/cm²,the cell voltage was reduced from 1.34 V to0.4 V.During the 4 h constant voltage test,the energy consumption was 78.32%lower than that of Nafion 115 membrane without catalyst.Although Pt has excellent catalytic activity,the disadvantages of high cost and short life have become the main obstacle to its practical application.In view of these problems,the research work was carried out in improving the activity,stability and reducing cost of catalysts.Carbon-supported Pt(Pt/C),reduced graphene oxide(RGO)-supported Pt(Pt/G)and RGO-carbon black supported Pt(Pt/GC)catalysts with a load of 60%were prepared by microwave-assisted alcohol reduction methode.The electrochemical oxidation performance of SO₂ was studied in high acid medium.The large two-dimensional planar structure of graphene was a better anchor for Pt nanoparticles and a catalyst with fine and uniform distribution of Pt particles was obtained.The carbon black interior prevented the agglomeration of graphene,forming a stereoscopic catalyst structure.The electrochemical surface area(ECSA)of Pt/GC and Pt/G catalysts was greater than Pt/C.In the CV test,the SO₂ oxidation peak current density of Pt/GC and Pt/G was 26.15%and 20.12%higher than Pt/C,respectively.The results showed that catalyst with carbon black-graphene as hybrid support had higher electrocatalytic activity than the catalyst with single support,which can be used in high efficiency and stable catalytic oxidation of SO₂ electrolytic cell.Generally,Pt alloy catalyst shows good electrochemical performance over Pt monometallic catalyst due to the electronic effect and synergistic effect,and also can reduce the amount of Pt.In this paper,the catalytic performance of Pt-Ru/C bimetallic catalysts with different nanostructures,namely Ru@Pt/C core-shell catalyst and Pt Ru/C alloy catalyst,for electrochemical oxidation of SO₂ was studied.The electronic effect and synergistic effect between Pt and Ru greatly improved the catalytic performance of Pt.The bimetallic catalyst contained large amount of Ru O_xH_y,which could promote the reaction.Ru@Pt/C showed good activity and stability in high acid environment.Due to the high utilization rate of Pt,the performance of Ru@Pt/C catalyst was higher than that of Pt Ru/C.The mass activity of unit metal of Ru@Pt/C and Pt Ru/C catalyst was 1.62 times and 1.26 times of Pt/C,respectively.In terms of unit Pt mass activity,the mass activity of Ru@Pt/C and Pt Ru/C were 2.43 times and1.73 times respectively as Pt/C catalyst.Based on the excellent properties of Ru@Pt/C catalyst,a series of Ru_x@Pt_y/C core-shell catalysts with different Ru/Pt molar ratios were prepared for the electrocatalytic oxidation of SO₂.Pt in the bimetallic catalysts is still dominated by metal state,but the element abundance of Ru oxidation state increased with the increase of Ru content.The matching degree between the catalytic activity and the electron effect was high,which indicated that electron effect was the main factor affecting the activity of the catalyst prepared in this paper.In the case of low coverage of Pt shell,that is,more Ru atoms were exposed on the surface,the main influencing factor of activity was bifunctional effect.Ru only played an auxiliary role in the reaction and did not directly catalyze the oxidation of SO₂.Under the same quality of metal loading,the electrocatalytic activity was highest when Ru/Pt molar ratio was 1:1.While the activity of unit Pt mass was the highest when Ru/Pt molar ratio was 3:1,which was 3.42 times of Pt/C.