Quantitative Judgement of ESL of Tungsten Oxide Based Electrochromic Energy Storage Devices

Regarding Electrochromic Energy Storage Devices (ECESDs), tungsten oxide could achieve greater capacity and richer colors if the suitable electrode is selected. There is a relationship between the energy storage level (ESL) of a bifunctional device based on tungsten oxide and its color, which is why qualitative information on the state of the device can be obtained directly.

The darker the color displayed on a tungsten oxide-based bifunctional device, the higher its ESL is when more charge is inserted into the EC film. The ideal use of tungsten oxide-based bifunctional electrochromic energy storage devices is in smart windows, as they can control the brightness and temperature in a room by changing the transmittance of sunlight to a comfortable state.

In addition, they can be used as a power source to drive small appliances such as light bulbs. Based on the positioning of such devices, it is natural and feasible to introduce photovoltaic solar cells. This idea is supported by the following reasons. First, the open-circuit voltage of the solar cells matches well with the low drive voltage associated with a dual-function tungsten oxide device. Second, their location in the building is not exclusive, so they can operate independently of each other, resulting in efficient energy use.

In general, the introduction of a solar self-powered section may take two main different forms. One is that the ECESDs and the sunlight conversion device are separate, and they are connected by wires outside the device. For example, researchers have connected tungsten oxide-based ECESDs to a silicon solar cell, a packaged crystal solar cell, and a dye-sensitized solar cell to implement a self-powered system. The results show that dual-function devices can be fully charged without an external power source. They can then output energy in a variety of forms, including lighting LED bulbs, and the entire process can be continuously monitored by the colors on the bifunctional devices.

Reference: Han W, Shi Q, Hu R. Advances in electrochemical energy devices constructed with tungsten oxide-based nanomaterials[J]. Nanomaterials, 2021, 11(3): 692.

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