Graphene Oxide-Based Planar Hygroelectric Generator and Its Applications in a Flexible Self-Powered Sensing System

This study reports a concept of a planar hygroelectric generator fabricated by nanosized graphene oxide (GO) flakes. On the surface of the GO film, flexible reduced GO (rGO) electrodes were fabricated by nanosecond laser irradiation, and a gradient of oxygen content between the anode and the cathode was established by electric polarization in a high-humidity environment. This device generates an open-circuit voltage of up to 0.6 V when the unit is placed in contact with moisture and has a good repeatability. Besides, material characterization methods such as Raman spectrum and X-ray photoelectron spectroscopy analyses have confirmed that the laser-irradiated GO area and the GO near the cathode have a lower oxygen content, and the hydroxyl groups (−OH) are mostly removed among all kinds of oxygen-containing functional groups. Therefore, a possible ion absorption theory was raised to explain the electricity generation mechanism in the nanoscale, in which the absorption of proton and the migration of OH– ions cause the charge transfer. In addition, this planar hydroelectric generator was successfully integrated with a resistive strain sensor to construct a fully flexible self-powered sensing system. The output voltage signal is controlled by both the environmental humidity and the strain change, providing a strategy to expand the application field of this hygroelectric generator to various sensing areas.