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

A series of proton-functionalized graphitic carbon nitride (fgC₃N₄) modified reduced graphene oxide (rGO)/nickel-aluminium layered double hydroxide (LDH) composites (fgC₃N₄-rGO/LDH-1 and fgC₃N₄-rGO/LDH-2) were prepared by a novel scalable strategy using different amounts of fgC₃N₄-rGO as a conductive matrix. The morphological analyses reveal that the LDH sheets are gradually assembled on the fgC₃N₄-rGO matrix. The fgC₃N₄-rGO and LDH mutually minimize their self-aggregation in fgC₃N₄-rGO/LDH composite. The porous skeleton of fgC₃N₄-rGO/LDH-1 (highest loading of fgC₃N₄-rGO matrix) produces a high surface area (240 m²/g) and mesopores (diameter; 2.2 nm). The fgC₃N₄-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-fgC₃N₄@rGO) was used as a negative material. The 3D-fgC₃N₄@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 fgC₃N₄-rGO/LDH-1 and 3D-fgC₃N₄@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 54.76 W h kg⁻¹ and 12031.92 W kg⁻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.