Recent Advances in Graphene-Based Humidity Sensors with the Focus on Structural Design: A Review

The advent of the 5G era means that the concepts of robot, virtual reality (VR)/augmented reality (AR), unmanned aerial vehicle (UAV), smart home, and smart healthcare based on Internet of Things (IoT) have gradually entered human life. Since then, intelligent life has become the dominant direction of social development. Humidity sensors, as humidity detection tools, not only convey the comfort of human living environment, but also display great significance in the fields of meteorology, medicine, agriculture, and industry. Graphene-based materials exhibit tremendous potential in humidity sensing owing to their ultrahigh specific surface area and excellent electron mobility under room temperature for application in humidity sensing. This review begins with the introduction of examples of various synthesis strategies of graphene, followed by the device structure and working mechanism of graphene-based humidity sensor. In addition, several different structural design methods of graphene are summarized, demonstrating that the structural design of graphene can not only optimize the performance of graphene, but also bring significant advantages in humidity sensing. Finally, key challenges hindering the further development and practical application of high-performance graphene-based humidity sensors are discussed, followed by presenting the future perspectives.