In 1972, Honda and Fujishima successfully used n-TiO₂ electrode to produce hydrogen from water by photolysis of solar energy, which made people realize the application prospect of Photoelectrochemical conversion of solar energy to electric energy and chemical energy. At the same time, this technology is applied to solve the problem of dye wastewater and other industrial wastewater.

Bactericide wastewater is a typical kind of toxic and harmful industrial wastewater which is difficult to degrade, such as wastewater from pesticide industry and some chemical industry. Because of the high concentration of bactericide in wastewater, it can kill and inhibit the growth of microorganisms. On the other hand, most of the organic fungicides are polycyclic or heterocyclic organic compounds with poor biodegradability. Therefore, it is difficult to treat the bactericide wastewater directly by biotechnology.

Electrochromism refers to the phenomenon that the optical properties (transmissivity, reflectance or absorptivity) of materials in the ultraviolet, visible or (and) near infrared region produce stable and reversible changes under the action of external electric field, which shows reversible changes of color and transparency in appearance.

Polluted wastewater and anti biotic wastewater are typical toxic and harmful industrial wastewater that are difficult to degrade, such as wastewater from pesticide industry and wastewater from some chemical industry. Because of the high concentration of fungicides in wastewater, which can kill and inhibit the growth of microorganisms, it is difficult to treat this kind of wastewater directly by biotechnology.