Recent Advances in Gas and Humidity Sensors Based on 3D Structured and Porous Graphene and Its Derivatives

Compared with two-dimensional (2D) graphene sheets, recently, three-dimensional (3D) structured and porous graphene has attracted much attention in gas and humidity sensing owing to its increased specific surface area, abundant reaction sites, and superior sensing performance. This review begins with the introduction of the device configurations and working mechanisms of 3D graphene-based gas sensors, followed by the elaboration of various synthesis strategies of 3D graphene. In addition to the gas-transducing properties of 3D and suspended graphene, the modification effect of metal oxides, small molecules, conductive polymers, noble metal nanoparticles, 2D materials, etc. on the gas-sensing performance of 3D graphene is also systematically discussed. 3D structured graphene not only performs as excellent gas-sensing material but also shows great advantages in humidity sensing due to its porous structure and a large number of adsorption sites for moisture. The humidity-sensing mechanism is elucidated to reveal the reactions between graphene and water molecules, followed by the introduction of devices. Finally, the existing key challenges that hinder the further development and practical application of 3D graphene-based gas/humidity sensors are presented, followed by proposing the future perspectives.