Capacitive sensor based on Green Synthesized Graphene Aerogel nanocomposite

The use of renewable energy, such as solar and wind power, is of great importance to meet the energy demands of a growing population, as non-renewable energy sources dwindle and the general public gain more knowledge on environmental pollution. One of the most important challenges in the energy storage industry is the design of energy storage devices from sustainable sources that have high energy capacity and high power capability[۱-۳]. Great efforts have been made to design and fabricate low-cost, high-efficiency advanced electrode materials for energy storage devices such as batteries and high-performance supercapacitors. Choosing organic and redox-active species that increase the Faradaic charge storage of electrode systems has thus become a challenge to increase energy density and conductivity[۴,۵]. To this aim, herein, azure A/۳D graphene aerogel (Az–GA) redox-active electrodes are fabricated via a hydrothermal and green method. Az links to ۳D GA via π–π interactions to form an anode. The new electrodes were synthesized via a one-step hydrothermal process and electrochemically characterized via cyclic۲voltammetry (CV) and galvanostatic charge-discharge (GCD) measurements. A modified Hummers’ method was used to synthesize graphene oxide (GO). To prepare Az–GA via a hydrothermal method, GO (۲۵ mg) was dispersed in water (۱۰ mL) in an ultrasonic bath for ۳۰ min. Then, a specific amount of Az chloride was added into the dispersed GO mixture, which was then ultrasonicated for a further ۳۰ min, during which time the color of the mixture changed from light brown to dark blue. Then, urea (۵۰۰ mg) as a reducing agent was added to the mixture, which was ultrasonicated for around a further ۱۰ min. Next, the mixture was transferred into a ۵۰ mL Teflon-lined stainless steel autoclave and heated at ۲۰۰ °C for ۶ h. The Az–GA was suspended on top of the solution, indicating the complete adsorption of azure molecules into the GA structure. The synthesized Az–GA was washed with a large amount of DI water to remove the impurities from the product. Finally, the Az–GA was frozen at −۷۰ °C and dried under vacuum. The same method was used to prepare Pure GA. An Az–GA/NF electrode was made using nickel foam as a current collector with a surface area of ۱.۰ cm۲ and ۳ M of KOH as an aqueous electrolyte. The nickel foam was then coated with a slurry containing ۸۵ wt.% of Az–GA, ۱۰ wt.% of carbon black, ۵ wt.% of PVDF, N-methyl-۲-pyrrolidone (NMP), and a small amount of DI water and pressed under ۵ MPs for ۱۰ s and dried at ۶۰ °C for ۱۲ h. Around ۱ mg of Az–GA was deposited on the NF as an anode for a supercapacitor. The Az–GA electrode exhibits good electrochemical performance and high specific capacitance of ۷۱۶.۰۶ F g−۱ at a current density of ۱ A g−۱.