Synthesis and multifunctional applications of ZnO-rGO composite in gas sensor and supercapacitor

Abstract

Zinc Oxide (ZnO) nanoparticles and reduced graphene oxide (rGO) nanosheets were synthesized using the Coprecipitation method and modified Hummer’s method, respectively. The nanocomposite of ZnO@rGO was then prepared via the ultrasonication method for NO2 gas sensing and as an electrode material for supercapacitor application. The ZnO@rGO films with different rGO compositions of 12 weight percentage (wt. %) (ZG-12), 15 wt. % (ZG-15), and 18 wt. % (ZG-18) exhibited percentage responses of 46%, 60%, and 51% at room temperature for 10 ppm NO2 gas. Similarly, these composite materials exhibited specific capacitance values of 233, 253, and 207 Fg-1, respectively, at a specific current of 0.5 Ag-1. Gas-sensing performance was optimized under various conditions (0.5–40 ppm gas concentrations, 25–100 °C temperatures, and 25–100% relative humidity). The sensor demonstrated excellent NO2 gas selectivity, with a detection limit of 0.5 ppm. This ZnO-rGO-based NO2 gas sensor offers a novel, room temperature-operating device with high response, reproducibility, and humidity tolerance. An asymmetric supercapacitor (ASC) device is fabricated using ZG-15 as the cathode and rGO as the anode electrode. This ASC device demonstrates a commendable specific energy density of 5.34 Wh kg−1 and a power density of 2.20 kW kg−1. Moreover, two such devices connected in series successfully illuminate red and green LEDs for over 5 and 3 min, respectively. This work provided successful insight into the multifunctional application of ZnO@rGO composite in the field of gas sensing and energy storage devices. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2025.