TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The method comprises: (a) providing tungsten trioxide thin film; (b) using tungsten trioxide thin film as a photoanode material of a photocatalytic electrolytic tank and adjusting the distance between the photoanode and the cathode in the photocatalytic electrolytic tank be 2-10 cm, and placing oxalic acid and electrolytic solution in the photocatalytic electrolytic tank; (c) bubbling the electrolytic solution by using an inert gas; (d) radiating solar light into the photocatalytic electrolytic tank; and (e) applying bias voltage to the photocatalytic electrolytic tank. The tungsten trioxide thin film is prepared by sintering method, anode oxidization method or sol gel method. The sintering method comprises cleaning and blow-drying the metal tungsten sheet and placing the sheet in a constant-temperature region of the vacuum tube furnace, heating the inner side of the tube to 140-160 degrees C at 8-12 degrees C/minute, feeding hydrogen, slowly increasing the pressure in the tube to reach 0.7-1.3 atm, and increasing the temperature in the tube to 790-810 degrees C, maintaining at 790-810 degrees C and cooling the tube to room temperature by nature. The anode oxidization method comprises cleaning and blow-drying the two tungsten sheets, placing into an anode oxidization tank filled with the electrolytic solution as an anode and cathode of the anode oxidization separately, where the distance between the two sheets is 2-10 cm, heating the electrolytic solution to 30-80 degrees C, supplying a constant voltage of 20-50 V between the anode and the cathode, performing anode oxidization for 2-5 hours, where the current of the whole anode oxidization process is increased from 0.01-1 A, taking out the anode sheet and washing with deionized water, blow-drying, placing the sheet in a constant temperature region of a vacuum tubular furnace, heating the inner side of the tube to 550-700 degrees C at 2-5 degrees C/minute under the protection of oxygen atmosphere, and maintaining the temperature for 2-4 hours and cooling the tube to the room temperature. The sol gel method comprises preparing nano tungsten trioxide paste of ethyl cellulose ethanol solution (15-25 g/100 g), coating the tungsten trioxide paste with a thickness of 2-8 mu m on a conductive glass, placing the glass in a constant-temperature region of the vacuum tube furnace, heating to 400-600 degrees C at 2-5 degrees C/minute, maintaining the heat for 20-60 minutes, heating the glass from 500-800 degrees C at 5-10 degrees C/minute, maintaining the heat for 5-15 minutes and cooling the to room temperature. Preferred Components: The amount of oxalic acid added is 1-9 g/100 g of solution. The material of the cathode of the photocatalytic electrolytic tank is platinum sheet, nickel net or and carbon-containing platinum sheet with a platinum quantity of 2-10%. The electrolytic solution is sulfuric acid or phosphoric acid with a concentration of 0.5-2 M. The size of tungsten trioxide is 1x 1 to 10x 10 cm. The bias voltage is 0.6-1.5 V. The bubbling process is carried out for 10-30 minutes. The solar light source is xenon lamp, where the intensity for filtering the ultraviolet light is 100 mW/cm2. The radiation light spot of the solar light is falls exactly at the center of the photoanode material.