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

Abstract

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 (NiI2) is found to be highly sensitive to moisture, and both its electrical properties and color will change with environmental humidity variation. Especially, NiI2 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 NiI2 can realize the detection of ultra-low humidity. The excellent performance of NiI2 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 NiI2 is developed to realize the dual-mode detection of wide range environmental humidity. These results demonstrate that NiI2 has great application prospects in professional ultra-low humidity detection and wearable humidity detection equipment.