Graphene is a singular layer of two-dimensional nanostructured sp2 carbon material that has attracted significant research in a variety of applications including, sensors 1, polymer composites 2, nanoelectronics 3, and energy storage as supercapacitors and various batteries 4, 5. The material possesses a high aspect ratio, exhibits exceptional electrical conductivity, and demonstrates favorable mechanical properties that appear to be the most alluring for supercapacitors right now. For supercapacitors, other graphene-based materials were also created, including a symmetric supercapacitor with a predetermined capacitance using chemically reduced graphene oxide 6, thermal reduction of GO to create a supercapacitor processing a specific capacitance of 132 F g − 1 in a 1 M H2SO4 electrolyte 7 and GO films that have undergone electrochemical reduction have a specific capacitance of 128 F g − 1 in 1 M NaNO3 8. Numerous techniques have been developed to create graphene to accomplish practical uses, most notably the arc discharge method 9, Chemical exfoliation, as well as chemical vapor deposition (CVD), and micromechanical fragmentation of highly oriented pyrolytic graphite (HOPG) 10. Liquid-phase exfoliation is one of them and is thought to be the most efficient approach for producing graphene on a wide scale and at a reasonable cost 11. GO may be chemically reduced to graphene using hydrazine or other reductants. It has also been discovered that supercapacitors with electrodes based on both graphene and graphene oxide exhibit high cyclic charge-discharge cycle life 12.
Much research has recently been undertaken to insert heteroatoms through the graphene scaffolding to create a bang gap by modulating an electron acceptor or a donor of electron characteristics, enhancing the capacitance and cycle stability in supercapacitors due to the low conductivity and inherent capacitance of graphene 13. To examine its capacitive performance, graphene has been doped with a variety of heteroatoms, including boron, nitrogen, oxygen, sulfur, and phosphor as well as their mixtures 14, 15. In their study, Yu et al. investigated the synthesis of graphene doped with X (where X represents either hydrogen (H2), iodine (I2), or bromine (Br2)) using the procedure of ball milling graphite with the addition of I2, Br2, and H2. The final product's specific capacitance and cycle ability were then assessed to determine whether or not it could be used as a supercapacitor electrode 21, all the X-doped graphene exhibits good electrochemical performance. Nitrogen-doped graphene has garnered the greatest interest within the dopants because, in addition to raising the charge carrier density, the N doping configuration results in a large interface capacitance, which is crucial for designing the electrode material of the supercapacitor. 16, 17. Nevertheless, the surface area is drastically reduced by agglomeration brought on by intense p-p contact, which lowers capacitance 18, 19. The catalytic activity of graphene can be enhanced by doping sulfur to the carbon cage; numerous studies have shown increased activity and performance in this regard. Doping sulfur with carbon results in a positive charge shift on nearby carbon. In general, doping nitrogen is recommended for modifying the electrical characteristics of carbon materials. However, because of the huge size of the sulfur, electron pairs that make up the doped sulfur are easily polarized and exhibit increased chemical activity 20, 21.
All graphene materials doped with X (X = heteroatoms as Cl, S, N, …) exhibit exceptional electrochemical performance due to their specific capacitance and prolonged stability. Nevertheless, it has been demonstrated that chlorine-doped graphene oxide increases capacity well, and high specific capacity has been reached because of the high degree of structural defects. 12, 22. Based on our comprehensive review of existing literature, it appears that the potential use of phosphoramide-functionalized graphene oxide (L-GO) in supercapacitor applications has not been thoroughly investigated. The using of all N, P, and S dopants in the massive ligand of phosphoramide which also can prevent agglomeration of graphene oxide is noticeable. Hence, it is anticipated that these phosphoramide-functionalized graphene oxide materials have significant promise to be used as electrode materials for supercapacitors. Based on the aforementioned reasons we first doped GO with Cl as its good performance and then substituted it with phosphoramide and compared them with each other.
This work presents the methodology employed for the synthesis of chlorine-doped graphene oxide (Cl-GO) and phosphoramide bis (5-amino-1,3,4-thiadiazol-2-yl) phenylphosphonotrithioate-funcltionalized graphene oxide (L-GO) using GO that has been firstly doped by Cl and then functionalized with L ligand, respectively. Herein, we introduced L in chloroform and triethylamine dropwise to dispersed Cl-GO and refluxed to synthesize the chlorine-doped graphene oxide (Cl-GO) functionalized with L ligand (L-GO) with enhanced capacitive performance. Due to the leaving group of Cl during the process of converting graphene oxide to L-GO, phosphoramide (L) is at the same time functionalized into the carbon scaffold in substitution with Cl. The incorporation of phosphoramide ligands into the graphene framework results in a significant enhancement of the surface area that is available for ions and electron mobility. This improvement in electrical has the potential to widely progress the internal resistance of the L-GO when used as electrode material. The L-GO electrode, with a bulk weight of 1.5 mg cm− 2, exhibits a notable increase in electrochemical performance. This results in a specific capacitance (Cg) of 206.8 F g − 1 at the current density of 1A g − 1. Furthermore, the L-GO material represents a great capacitance retention of 72.6% under a higher current density of 50 A g − 1, providing a specific capacitance of 150.1 F g − 1.