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Abstract Humidity sensors are essential components in wearable electronics for monitoring of environmental condition and physical state. In this work, a unique humidity sensing layer composed of nitrogen‐doped reduced graphene oxide ( n RGO) fiber on colorless polyimide film is proposed. Ultralong graphene oxide (GO) fibers are synthesized by solution assembly of large GO sheets assisted by lyotropic liquid crystal behavior. Chemical modification by nitrogen‐doping is carried out under thermal annealing in H 2 (4%)/N 2 (96%) ambient to obtain highly conductive n RGO fiber. Very small (≈2 nm) Pt nanoparticles are tightly anchored on the surface of the n RGO fiber as water dissociation catalysts by an optical sintering process. As a result, n RGO fiber can effectively detect wide humidity levels in the range of 6.1–66.4% relative humidity (RH). Furthermore, a 1.36‐fold higher sensitivity (4.51%) at 66.4% RH is achieved using a Pt functionalized n RGO fiber (i.e., Pt‐ n RGO fiber) compared with the sensitivity (3.53% at 66.4% RH) of pure n RGO fiber. Real‐time and portable humidity sensing characteristics are successfully demonstrated toward exhaled breath using Pt‐ n RGO fiber integrated on a portable sensing module. The Pt‐ n RGO fiber with high sensitivity and wide range of humidity detection levels offers a new sensing platform for wearable humidity sensors.
Choi et al. (Wed,) studied this question.