Ethyl viologen diiodide is primarily used as an electron transfer agent in various electrochemical applications. It is commonly employed in electrochromic devices, where it facilitates color changes in response to electrical stimuli, making it useful in smart windows and displays. Additionally, it serves as a redox mediator in biosensors, enhancing the detection of biological molecules by improving electron transfer efficiency. In research, it is utilized to study electron transfer processes in chemical and biological systems, aiding in the development of advanced materials and technologies. Its ability to undergo reversible redox reactions makes it valuable in energy storage systems, such as redox flow batteries, where it contributes to efficient energy conversion and storage.