A self-powered moisture detector using graphene oxide film constructed by asymmetric metal electrodes

Self-powered touchless moisture sensor is highly demanded in human-machine interactive systems, which can be used to track the finger spatial position. Moisture sensors using graphene oxide (GO) film as sensing materials reported so far were generally working under bias voltage, which should be pre-treated by asymmetric electrical reduction under high bias voltage. Herein, it is found that the oxygen-containing chemical group gradients in GO film can be prepared via synchronous reduction by introducing asymmetric metal electrodes, such as Au vertical bar Cu, Au vertical bar Zn, and Au vertical bar Al, without any electrical reduction treatment. A moisture-triggered power generator was readily configured upon alternative exposure to low and high relative humidity. We further confirmed that device with planar configuration showed much higher power density than sandwiched device. On the basis of such nanogenerator with Au vertical bar Zn electrodes, a self-powered moisture detector exhibited Delta I/I-0 of 2800 when finger was positioned at distance of 0.2 cm. Importantly, finger spatial position was sensitively detected on 5 x 5 sensor array in touchless mode. Present work develops a simple and effective way for energy harvesting system using GO as sensing material in a zero energy cost way, also builds a promising self-powered moisture sensor for touchless detection of humid objects. (C) 2019 Elsevier B.V. All rights reserved.