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.