Preparation And Application Of Oxygen Group Metal Semiconductors （WO₃）in Energy Conversion

Tungsten trioxide（WO₃）is a typical material in the oxygen-group metal semiconductors,with a band gap of 2.5-2.8 e V.WO₃has several merits,as good response in the visible light range,low environmental harm,simple preparation method,and good stability in acid environment.WO₃shows great development potential in the field of solar hydrogen production and degradation of organic pollutants.Therefore,WO₃is considered a promising photocatalytic material.But now,the photocatalytic activity of WO₃is mainly affected by the serious charge recombinations and low charge migrations.Thus,many researchers have tried to solve the above shortcomings by optimizing the morphologies,employing elemet doping with metals and non-metal ions,crystal plane engineering and semiconductor composite construction of heterojunction.In this paper,WO₃has been modified by compounding with n-type semiconductor and treating with sodium hydroxide solution.After preparing WO₃nanosheets and WO₃/Bi VO₄heterojunction through hydrothermal and spin coating methods,surface treatment of WO₃/Bi VO₄heterojunction was conducted by sodium hydroxide solution,with morphological characterization,photoelectrochemical test and hydrogen production analysis.The research content of this paper could be divided into the following two aspects:1.To construct WO₃/Bi VO₄heterojunction.The WO₃seed layer was prepared on the FTO conductive glass by spin coating.Then the WO₃nanosheet was prepared by hydrothermal method.Finally,the Bi VO₄precursor solution was spin-coated on the surface of the WO₃nanosheet,and the WO₃/Bi VO₄heterojunction was obtained after thermal annealing.Under standard solar spectrum conditions,the WO₃/Bi VO₄heterojunction exhibited excellent photocatalytic performance in sodium sulfate electrolyte compared to pure WO₃nanosheets.Compared the photocurrent performance of WO₃nanosheets and WO₃/Bi VO₄heterojunction,the photocatalytic activity was enhanced by effective separation of photo-generated electron（e^-）-hole（h⁺）pairs.At the same time,because the Bi VO₄particles attach to surface of the WO₃nanosheets,the specific surface area is increased.In summary,the photocatalytic activity has been significantly improved.The preparation of WO₃and its heterojunction has the advantages of cost-effectiveness and high controllability,which is expected to become a preferred material for photocatalytic water decomposition.2.Sodium hydroxide solution was used for surface treatment of WO₃/Bi VO₄heterojunction.In this article,the WO₃/Bi VO₄heterojunction was treated for different times by using 0.5 mol/L sodium hydroxide solution.Through morphological characterization and phase analysis,it was observed that the rough morphology of the sample after sodium hydroxide treatment did not change significantly.but the Bi VO₄particles attached to the surface of WO₃were more obvious.Through transmission electron microscopy,it was observed that the bismuth vanadate particles of the sample after sodium hydroxide treatment had clearer edges,which could indicate that the surface chemical state of the bismuth vanadate particles was optimized.The impedance of the sample after sodium hydroxide treatment was significantly reduced by electrochemical impedance spectroscopy,and the photocatalytic activity of the sample was improved.The WO₃/Bi VO₄heterojunction after treatment with sodium hydroxide solution has more excellent photocatalytic water decomposition ability,compared with the pure WO₃and WO₃/Bi VO₄heterojunction.Under illumination,the WO₃/Bi VO₄heterojunction after treatment with sodium hydroxide solution has the highest photocurrent density at 1.23 V vs.RHE（Reversible hydrogen electrode）,which is 1.76A/cm²,perform 2.45 and 1.2 times of pure WO₃nanosheet and WO₃/Bi VO₄heterojunction did,respectively.This treatment method is great significance for the photocatalysts of oxygen-group metal semiconductors,due to its convenient operation and simplicity.