Researchers have pioneered the use of non-metallic iodine as the base for electrochromic dynamic windows, presenting a breakthrough opportunity for energy-efficient designs and contributing to the advancement of smart materials.
Traditionally, electrochromic materials employed inorganic compounds like tungsten oxide, which frequently presented challenges, including limited color neutrality and issues with cycling stability. This revolutionary study showcases how non-metallic iodine, when paired with water-in-salt electrolytes, overcomes these hurdles, achieving high optical contrasts and remarkable self-healing capabilities.
Electrochromism allows materials to change their optical properties—such as how much light they absorb or reflect—when exposed to electricity. The typical route for achieving this involved alterations to the oxidation states of metals under electrical stimulation. But iodine has typically eluded substantial use because of its molecular crystal structure and poor conductivity, which limited its effectiveness. A team of researchers decided to address these shortcomings by exploring how liquid electrolytes could stabilize solid iodine deposition, facilitating the reversible transformations needed for electrochromism.
By creating iodine electrodeposition-based electrochromic dynamic windows, the researchers achieved remarkable performance metrics. The device produced optical contrasts of 76.0%, maintaining color neutrality during its operation. After enduring 6001 cycles of color transformation, it retained 69.4% of its optical performance, demonstrating its remarkable durability and stability.
This project utilized water-in-salt (WiSE) electrolytes—an unconventional electrolyte system—where the concentration of water is low, minimizing the dissolution of iodine and the shuttle effect commonly seen with traditional electrolytes. This unique condition allows for efficient interactions between the iodine and the electrolyte, ensuring adherence to the electrode surfaces and achieving stable coloration and bleaching cycles.
Crucially, when subjected to electrical stimuli, the system could effectively produce dark brown iodine on its surface, blocking visible light's passage. Once the voltage was removed, it quickly transitioned back to transparency by converting the iodine to colorless iodide ions. This quick response time enhances practicality for applications like smart windows, which can save energy by limiting solar heat gain and providing interior comfort.
Notably, the incorporation of self-healing properties marks significant progress from previous electrochromic systems. Iodine is known to perform poorly under varied atmospheric conditions, but the unique environment created through WiSE electrolytes mitigates sublimation risks, promoting stable long-term usage.
To confirm the efficacy and durability of the device, the researchers executed extensive cycling tests, illustrating strong resilience across 2000 cycles, with retained optical modulation rates of up to 91.3%. These findings are promising as they suggest potential scalability for commercial applications.
This innovation not only opens up avenues for the rapid development of next-generation electrochromic devices but also emphasizes the importance of exploring non-metallic materials. Given the rising demand for energy-efficient building solutions, the researchers believe their findings could lead to significant breakthroughs in smart window technology.
With many commercial, architectural, and technological applications on the horizon, this revolutionary approach to electrochromic materials redefines expectations and paves the way for increased energy efficiency and sustainability.