Engineered separator of cellulose/ionic-liquid for the fabrication of a novel device with H-type architecture and dual function: Supercapacitor and NO2 gas sensor

Abstract

This investigation presents the fabrication of integrated dual-devices that work as supercapacitor or NO2 gas-sensor. Those devices were constructed with a novel H-type architecture, which allows the control of the separation distance between electrodes (d = 0.4 or 0.8 cm). Firstly, SCs were made with d = 0.8 cm and graphene (GR) electrodes (GR-SC/0.8 device), those ones produced the highest capacitance/energy–density of 284.6F/g/40.6 Wh kg−1. Next, SCs were made with composite electrodes of graphene/La0.2Gd1.8Zr2O7 + La0.7Sr0.3MnO3-perovskite (LGZM) and the weight ratio of GR/LGZM varied from 1/1 to 0.7/1.3. SCs made with GR/LGZM ratio of 1/1 and d = 0.8 cm produced a higher capacitance/energy–density of 378.3F/g/52.5 Wh kg−1. Devices made with a separation distance of 0.4 cm had lower capacitances of 56–72.7F/g, but presented a battery behavior (not observed in the devices made with d = 0.8) that generated capacities of 787–866 mAh/g. Interestingly, increasing the separation distance from 0.4 to 0.8 in the devices made with GR + LGZM increased their capacitance by 268–571 %. Raman and XPS analyses demonstrated that the redox centers for the charge storage in the SCs made with the LGZM-perovskite were the oxygen vacancies, Mn3+/Mn4+ and Gd0/Gd3+ species. Later, the dielectric separator of the GLGZM1/1-SC/0.4 device was coated by a layer of ionic liquid [BMIM][BF4] and this modified device (sensor) was exposed to NO2 gas. Consequently, NO2 gas (100 ppm) was detected with response/recovery times of 11.6/178.8 s (its gas-response was 10.3). For reference purposes, a similar sensor was made with only graphene electrodes, but it had higher response/recovery times of 17.1/284.2 s and lower gas-response of 5.9. Hence, the dual-devices could provide energy and detection of noxious gases, which is attractive for wearable electronics.