Heteropolyacids have been developed for more than 100 years, and the research contents have been gradually extended to material chemistry, electrochemistry, catalytic chemistry, photochemistry, surface science, medicine and other fields. Therefore, heteropolyacids show high catalytic activity and selectivity for various organic reactions.

Electrochromism refers to the phenomenon that the optical properties of materials change reversibly under the action of external electric field. Electrochromism only needs a small voltage (about 2V) to work. In the open circuit state, it can keep the original color or fading state unchanged, so it consumes less energy.

Tungsten oxide (WO₃) thin film is an ideal electrochromic and energy storage material due to its high contrast, good stability of crystal structure, strong environmental affinity and low cost. It is found that the smart window dual-function device based on the tungsten oxide film of indium ferrocyanide includes two conductive substrates as the working electrode and the reference electrode, one of which is coated with the tungsten oxide film on the surface of the conductive substrate to form the reference electrode structure, the other is coated with the indium ferrocyanide film on the surface of the conductive substrate to form the working electrode structure. The preparation steps of the film are as follows:

Tungsten trioxide electrode and its preparation method, and its application in photo catalytic decomposition of water use semiconductor photo catalytic technology to convert solar energy into hydrogen energy through water decomposition, and store and use hydrogen in the form of chemical energy, is one of the most promising ways to solve the current energy crisis.