Study On Anode Catalysts For Electrochemical Ozone Production In A Proton Exchange Membrane Water Electrolyzer

Ozone（O₃）has the advantages of strong oxidation,strong disinfection ability,clean and harmless,and has been widely used in many occasions,such as organic synthesis,disinfection,sewage and waste gas treatment,bleaching industry,etc.Electrochemical ozone production（EOP）technology can produce O₃with high concentration based on the principle of water electrolysis.The simple and lightweight proton film water electrolyser（PEMWE）can produce O₃more efficiently and on a large scale.Fluorine（F）doped lead dioxide（PbO₂）prepared by electrodeposition is one of the most commonly used EOP anode materials because of its high EOP activity,high conductivity,relative stability and low cost under acidic condition.However,at present,there is a lack of in-depth understanding of the special enhancement effect of F-containing components on the activity of EOP catalysts,partly due to the lack of in-depth studies on the formation mechanism of O₃and the structure-activity relationship.As an important intermediate for O₃generation,the role of O₂in the mechanism of O₃generation has received little attention.In this paper,we chose the classical catalyst-PbO₂as the research object,to explore the role of O₂in the formation of O₃,and a more comprehensive study of doping F on the structure and properties of PbO₂electrode,in order to enhance understanding of the special enhancement effect of F-containing components.In view of the limited electrode area,low catalyst activity,large amount of raw material and complex processing process of electrodeposition preparation method,we explore a a simple chemical synthesis method to prepare PbO₂microspheres catalyst for efficient production of O₃.This method can also achieve accurate regulation of the crystal phase composition and grain size of the catalyst.It is also convenient to further study the structure-activity relationship of PbO₂catalyst.The use of lead is easy to cause environmental pollution and threaten human health.We try to replace toxic PbO₂with Ir O₂-Ta₂O₅coating catalyst of lead-free system in proton membrane hydrolysis ozonator,and study the origin of O₃-producing activity of Ir O₂-Ta₂O₅coating catalyst of a series of components.Its performance and stability in preparing O₃from PEMWE is evaluated.The main research results are as follows:1.PbO₂electrodes doped with different amounts of F were prepared by electrodeposition,and the effects of F doping on the structure,morphology,electrochemical properties and surface interface properties of PbO₂electrodes were studied.It was found that theαphase of the impurity could be completely inhibited by doping a right amount of F,and the e-0.5F-PbO₂and e-1.5F-PbO₂obtained by electrodeposition were both pureβ-PbO₂,which inhibited the side reaction of oxygen evolution and was conducive to the enhancement of the activity of EOP.The F component on the electrode surface also occupies part of the active site of water oxidation,which enhances the hydrophobicity of the electrode and the adsorption of O₂on the electrode surface,which is conducive to the generation of O₃.The role of O₂in the electrocatalytic formation of O₃at PbO₂anode has been verified by in situ isotope(¹⁸O₂)labeling experiments and electrochemical cell-online mass spectrometry.It is found that O₂can also be used as a raw material for the formation of O₃in addition to the solvent H₂O.A corresponding mechanism model is proposed to illustrate this experimental finding,that is,O₂molecules can adsorb and dissociate on PbO₂electrode surface at room temperature,which can then fill the oxygen vacancy caused by O₃precipitation,thus promoting the continuation of O₃generation process dominated by LOM mechanism.2.A simple atmospheric hydrothermal oxidation method was used to synthesize a PbO₂microspheres catalyst for efficient production of O₃.Due to its larger surface area and pureβphase,the catalyst prepared by chemical method has higher O₃generation activity,stability and device performance than electrodeposited PbO₂.By adjusting the phase ratio/primary grain size of PbO₂microspheres with a series of high concentration of Na OH solution,it is found that the activity ofβphase is much higher than that ofαphase for EOP reaction.The largerβ-PbO₂grain size（or crystallity）is more favorable for EOP reaction,while the smallerαphase and grain size are more favorable for OER reaction.3.A series of Ir O₂-Ta₂O₅coated titanium electrodes were prepared by thermal decomposition method to study the role of Ir O₂and Ta₂O₅in the formation of O₃.The role of Ir O₂is to enhance the electronic conductivity of the coating,but the side effect of too strong O₂analysis activity leads to the low O₃analysis current efficiency of the coating electrode.Ta₂O₅is the active phase of EOP.One part of Ta₂O₅is concentrated on the surface of the coating in an amorphous form,covering most of Ir O₂in a physical way,while the other part can be incorporated into the lattice of Ir O₂,causing lattice expansion and transferring charge from Ta to Ir.Ta₂O₅in both parts can effectively inhibit the O₂evolution activity of Ir O₂components on the surface of the coating.This is conducive to the generation of O₃.The stability,activity and working current density of the electrode were improved by adding Sb-Sn O₂interlayer.The optimized Ti/Sb-Sn O₂/40Ir O₂-60Ta₂O₅coated electrode has an O₃yield of 45 mg/h and a current efficiency of 2%when working at 1 A·cm^-2in a PEM water electrolyzer.