Preparation Of WO₃ Photoanode And Its Photoelectrocatalytic Performance For Glycerol Selective Oxidation

Selective oxidation of glycerol can produce a variety of high-value products（aldehydes,ketones and carboxylic acid compounds）,which is an important way for the value-added transformation of glycerol.At present,the selective oxidation of glycerol mainly adopts thermal catalysis and enzymatic catalysis methods,and there are common problems such as high catalyst cost,difficult control of target product selectivity,and unfriendly environment.The photoelectrochemical method can use low-cost semiconductor catalysts to selectively oxidize glycerol with sustainable solar energy and electrical energy to prepare high value-added products,which has the advantages of green environmental protection and sustainability.The key to photoelectrochemical selective oxidation of glycerol is to develop photoanode with high activity,high product selectivity and high stability.WO₃ has the advantages of excellent electron transport performance,visible light absorption and photocorrosion resistance,and is widely used in photoelectrochemical water splitting;however,WO₃ has problems such as serious carrier recombination and poor stability,and there is no report of its use in photoelectrochemical glycerol oxidation.In this thesis,WO₃ was modified by the methods of crystal face control and oxygen vacancy construction,and WO₃ photoanodes with different morphologies and surface properties were prepared,and their photoelectrochemical performance for the selective oxidation of glycerol was studied.Using XRD,SEM,TEM,ESR and other technical means,the physicochemical properties of the prepared WO₃ photoanode were analyzed and characterized,and the structure-effect relationship between the structure and performance of the WO₃ photoanode was explored.The main findings of this study are as follows:1.Using the secondary hydrothermal method,by changing the hydrothermal time and the dosage of ammonium oxalate monohydrate,the crystal face exposure ratio of WO₃ was regulated.A WO₃ photoanode with mainly exposed{202}crystal planes（hereinafter referred to as WO₃{202}）was prepared for the first time.Through experiments and theoretical calculations,the difference between WO₃{202}and WO₃{200}photoelectric catalytic oxidation of glycerol was studied.The results show that WO₃{202}has more excellent photoelectrocatalytic performance,and the formation rate and selectivity of glyceraldehyde can reach 462 mmol h^-1 m^-2 and 80%,respectively.It is attributed to the exposure of the{202}crystal face of WO₃,which is beneficial to its light absorption,charge transport and its adsorption to the terminal hydroxyl group of glycerol.2.Using WO₃ nanosheets as photoanode,the factors affecting the stability of WO₃photoanode in the catalytic oxidation of glycerol were investigated.The effects of illumination,immersion in electrolyte,and applied potential on the stability of WO₃ photoanode were compared,and it was found that the main reason for the stability of WO₃ photoanode was that the applied high potential was the main reason.Continued application of a high potential causes the WO₃ photoanode to generate surface states,which introduce electron-hole recombination centers,resulting in a rapid decline in its activity.The low-potential treatment can eliminate the surface state and restore its activity.In addition,the introduction of oxygen vacancies can suppress the generation of surface states and enhance the stability of the WO₃ photoanode,in which O_V-WO₃-350 maintains 40 h no decrease in activity during the stability test.