Application of moisture-induced discoloration material Nickel(II) iodide in humidity detection

Ultra-low humidity detection is significant in some important industrial fields, such as integrated circuit manufacturing, chip packaging. However, the traditional ionic-type humidity sensor is not competent for the detection of ultra-low humidity, but can only realize the detection of medium humidity to high humidity. Here, moisture-induced discoloration material Nickel(II) iodide (NiI 2 ) is found to be highly sensitive to moisture, and both its electrical properties and color will change with environmental humidity variation. Especially, NiI 2 exhibits the largest impedance change to date in the ultra-low humidity range compared with state of the art. The impedance variation is up to 2 orders of magnitude in the range of 0.4 %–11 % RH, which means that NiI 2 can realize the detection of ultra-low humidity. The excellent performance of NiI 2 in ultra-low humidity is attributed to the material transition characteristics susceptible to humidity rather than the traditional surface mechanism of water adsorption. Moreover, combining the reversible black-to-transparency moisture-induced discoloration behavior with humidity sensing properties, a flexible wristband based on NiI 2 is developed to realize the dual-mode detection of wide range environmental humidity. These results demonstrate that NiI 2 has great application prospects in professional ultra-low humidity detection and wearable humidity detection equipment.