Oxygen-Rich Hierarchical Porous Graphene as an Excellent Electrode for Supercapacitors, Aqueous Al-Ion Battery, and Capacitive Deionization

In this study, we have described the synthesis of oxygen-rich hierarchical porous graphene (O-PG) using focused solar radiation on nitric acid treated graphene oxide film. This nitric acid treatment for graphene oxide helps in generating micropores on the graphene sheets and introducing oxygencontaining functional groups when solar light is focused. This unique hierarchical porous structure along with high surface area and oxygenated functional groups makes O-PG as suitable electrode in energy storage and also for capacitive deionization. The as-prepared O-PG exhibits high specific capacitance of 354 F g(-1) along with energy storage of 110.6 Wh kg(-1) at 1 A g(-1) current density. O-PG also delivers high specific capacity of 90 mAh as high-performance cathode in aqueous Al-ion battery with an exceptionally high cyclic stability up to 10 000 cycles of charging-discharging processes at high current density of 0.5 A g(-1). In addition, the electrosorption studies of salt ions were done using capacitive deionization technique. The extraordinary salt removal capacity of 21.1 mg g(-1) has been obtained for 500 mg L-1 NaCl solution at voltage of 1.4 V. This material removes not only NaCl from salty water but also other major salts such as MgCl2 and Ca(SO4)(2). Hence, this work demonstrates a simple way of utilizing solar radiation to prepare high-performance O-PG and its applicability as an excellent electrode in high-energy supercapacitors, aqueous Al-ion battery, and capacitive deionization.