Chitosan/citric acid modified laser induced graphene self-powered sensor: Achieving non-contact humidity monitoring using ionic gradients

In recent years, non-contact wearable humidity sensors have become increasingly important in the monitoring of human respiratory health. However, there are challenges in manufacturing high-performance, convenient, and energy-saving sensors at a low cost. This paper proposes a wearable self-powered humidity sensor based on a chitosan/citric acid-laser-induced graphene (CS/CA-LIG) composite film and simulating a primary battery through a sandwich structure. The upper film absorbs water molecules in the air, and protons in the film diffuse downward driven by the humidity difference. In addition, the mechanism of how zinc/copper electrodes increase the current output performance relying on the redox potential difference is explored, so as to convert the chemical/electrochemical potential generated by humidity gradients and chemical energy into electrical energy, and thus generate electricity through humidity. The proposed self-powered humidity sensor exhibits high sensitivity and response speed when sensing different air humidities. Meanwhile, the proposed CS/CA-LIG sensor has a wide humidity sensing response in the range of 11 %–98 % RH, with a sensitivity of S = 2.01 mV/RH%. We attach the sensor to a mask in a non-contact form to monitor the breathing situation, and also attach it to some parts of the body to monitor the breathing state. By monitoring the amplitude and frequency of its electrical signals, some health conditions of the human body can be sensed. Therefore, this study provides valuable references for non-contact self-powered sensors and is of great significance in the fields of energy issues and medical health sensors.