Modified electrochemical charge storage properties of h-BN/rGO superlattice through the transition from n to p type semiconductor by fluorine doping

Abstract

A band gap of ∼2.1 eV was obtained through the hybridization of reduced graphene oxide (rGO) with insulating hexagonal boron nitride (h-BN). The h-BN/rGO superlattice behaved like n type semiconductor due to the enriched electron density at the conduction band and allowed charge transfer depending on the redox potential of the electrolyte. The band gap energy was further minimized to ∼1.79 eV through fluorine (F) doping within the h-BN/rGO. F doping created population density near the valance band and the Fermi level shifted towards the lower energy level. F doped superlattice behaved like p type semiconductor where F was adsorbed mostly at the N site. It is noticed that the contribution of the redox charge transfer to the overall capacitance was increased in comparison to the electrochemical double layer capacitance with increasing F doping. The formation of defects and disorder due to doping provided facile diffusion path enhancing the charge storage contribution from the interior site of the electrode materials. The specific capacitance of the F doped h-BN/rGO superlattice was determined as 1250 F g−1 which is 130% of un-doped sample. An asymmetric supercapacitor (ASC) cell was fabricated with F doped h-BN/rGO superlattice, which showed almost zero IR drop, high stability (∼77% retention of capacitance after 10,000 charge–discharge cycles) and large energy and power density of 87.5 W h kg−1 and 6300 W kg−1, respectively. Furthermore, the ASC also exhibited very low relaxation time constant of ∼0.39 ms ensuring effective power delivery and quick charge–discharge capacity.