Flexible Humidity Sensor Based on a Graphene Oxide–Carbon Nanotube-Modified Co₃O₄ Nanoparticle-Embedded Laser-Induced Graphene Electrode

Abstract

To meet evolving humidity monitoring needs, the development of flexible, high-performance humidity sensors is crucial. This study introduces an innovative flexible humidity sensor using a single-step laser scribing technique to fabricate a flexible in situ Co₃O₄ nanoparticle-embedded laser-induced graphene (Co₃O₄-LIG) composite electrode. Compared to conventional LIG electrodes, the Co₃O₄-LIG electrode exhibits improved conductivity and hydrophilicity, enhancing charge transfer and water molecule affinity. The unique two-dimensional structure and exceptional water permeability of graphene oxide (GO) combine with the rapid water response and high specific surface area of carboxylated multiwalled carbon nanotubes (MWCNTs), thereby assuming a crucial function in the modification and optimization of the performance of humidity sensors. Through the application of a homogenously blended aqueous solution comprising GO and MWCNTs in precise proportions onto the Co₃O₄-LIG composite electrode, an excellent humidity-responsive layer is established, culminating in the realization of a cutting-edge GO-MWCNTs@Co₃O₄-LIG flexible humidity sensor. Noteworthy attributes of this sensor include a heightened sensitivity [959.1% (Δ<i>R</i>/<i>R</i>₀)], rapid response and recovery times (within 5 and 26 s, respectively), and a noteworthy linearity (<i>R</i>² = 0.994) across a relative humidity range of 14 to 95%. The findings presented herein offer valuable insights and a practical blueprint for the design and production of flexible humidity sensors.