Rainbow‐Colored Carbon Nanotubes via Rational Surface Engineering for Smart Visualized Sensors

Abstract Surface engineering is effective for developing materials with novel properties, multifunctionality, and smart features that can enable their use in emerging applications. However, surface engineering of carbon nanotubes (CNTs) to add color properties and functionalities has not been well established. Herein, a new surface engineering strategy is developed to achieve rainbow‐colored CNTs with high chroma, high brightness, and strong color travel for visual hydrogen sensing. This approach involved constructing a bilayer structure of W and WO3 on CNTs (CNT/W/WO3) and a trilayer structure of W, WO3, and Pd on CNTs (CNT/W/WO3/Pd) with tunable thicknesses. The resulting CNT/W/WO3 composite film exhibits a wide range of visible colors, including yellow, orange, magenta, violet, blue, cyan, and green, owing to strong thin‐film interference. This coloring method outperforms other structural coloring methods in both brightness and chroma. The smart CNT/W/WO3/Pd films with porous characteristics quickly and precisely detect the hydrogen leakage site. Furthermore, the smart CNT/W/WO3/Pd films allow a concentration as low as 0.6% H2/air to be detected by the naked eye in 58 s, offering a very practical and safe approach for the detection and localization of leaks in onboard hydrogen tanks.