Graphitic carbon nitride modified graphene/Nie-Al layered double hydroxide and 3D functionalized graphene for solid-state asymmetric supercapacitors

A series of proton-functionalized graphitic carbon nitride (fgC(3)N(4)) modified reduced graphene oxide (rGO)/nickel-aluminium layered double hydroxide (LDH) composites (fgC(3)N(4)-rGO/LDH-1 and fgC(3)N(4)-rGO/LDH-2) were prepared by a novel scalable strategy using different amounts of fgC(3)N(4)-rGO as a conductive matrix. The morphological analyses reveal that the LDH sheets are gradually assembled on the fgC(3)N(4)-rGO matrix. The fgC(3)N(4)-rGO and LDH mutually minimize their self-aggregation in fgC(3)N(4)-rGO/LDH composite. The porous skeleton of fgC(3)N(4)-rGO/LDH-1 (highest loading of fgC(3)N(4)-rGO matrix) produces a high surface area (240m(2)/g) and mesopores (diameter; 2.2 nm). The fgC(3)N(4)rGO/LDH-1 electrode generates a specific capacitance value of 1190 F g(-1) at 1 A g(-1), excellent rate performance (71% at 10 A g-1), and good cycling stability (90% after 3000 cycles), in a three-electrode setup. Hierarchical fgC3N4 functionalized rGO composite (3D-fgC(3)N(4)@rGO) was used as a negative material. The 3D-fgC(3)N(4)@rGO produces an excellent capacitance of 345 F g(-1) at 1 A g(-1), high rate capability (74% at 10 A g(-1)) and good cyclic stability (90% after 3000 cycles). The fgC(3)N(4)-rGO/LDH-1 and 3D-fgC(3)N(4)@rGO were assembled to fabricate a solid-state asymmetric supercapacitor device using KOH/PVA gel electrolyte. The device operates within the potential window of 1.6 V and produces the highest energy density and power density of 54.76Wh kg(-1) and 12031.92Wkg(-1), respectively. The solid-state device shows an excellent cycle life of 91% after 7000 cycles, and it can power a red LED, suggesting very efficient for practical application.