Hydrothermal Method Prepares Tungsten Trioxide Photoanode

Hydrothermal method is the scope of liquid chemical method. It means in chemical reaction, a sealed pressure vessel with water as a solvent, carried out at high temperature and pressure conditions. Hydrothermal reaction depends on the type of reaction that can be divided into hydrothermal oxidation, water and heat reduction, hydrothermal precipitation, hydrothermal synthesis, water hot solution, hydrothermal crystallization. So the hydrothermal method is the most popular method in crystallization.

Experimental Procedure
The polished clean tungsten sheet was placed in distilled water and ultrasonic cleaning in ethanol were 10min, after drying and controlling the temperature in a muffle furnace at 450 ℃, the tungsten trioxide layer is formed in the calcinations of 30min. Hydrothermal reaction solution of polyethylene glycol (300) 10% is prepared by volume of 0.02mol / L sodium tungstate solution, the solution was adjusted pH2.0 with 3mol / L hydrochloric acid. 25ml of the solution is placed in the Teflon reactor and the tungsten sheet vertically was placed in a pre-oxidized, the reaction temperature is controlled at 180 ℃ 6h. The reaction product was removed with distilled water soak about 10min, and repeating it three times to remove the product surface residue, and then the preparation of tungsten trioxide photoanode is completed after drying calcining at 550 ℃ 180min.

Conclusions
1. Hydrothermal preparation method can generate highly ordered nano-strip structure of tungsten surface, it can reach 1.5V 1.8mA / cm2in the photoanode of current;
2. a curve is made from oxidation of the tungsten film, corresponding to WO₃ cubic phase in the oxidation process of 450 ℃ , the oxide layer will be formed on the surface of the tungsten sheet;
3. b curve is hydrothermal reaction product that is not calcined WO₃, corresponding to the orthorhombic WO₃;
4. c curve is the calcined WO₃, corresponding to the monoclinic WO₃, which shows three distinct peaks, the highest peak meter bar is vertically grown on the substrate, the height can reach 6.91 microns, which in shows excellent orientation role of tungsten oxide layer of the substrate with polyethylene glycol in the hydrothermal reaction of crystal growth.

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