Engineering Architecture of 3D-Urchin-like Structure and 2D-Nanosheets of Bi₂S₃@g‑C₃N₄ as the Electrode Material for a Solid-State Symmetric Supercapacitor

In this work, uniform hierarchical mesoporous 3D-urchin-like Bi₂S₃@2D-nanosheet g-C₃N₄ was synthesized via a superficial hydrothermal method. The prepared pristine Bi₂S₃, g-C₃N₄, and 3D-Bi₂S₃@2D-g-C₃N₄ composite samples were extensively studied for their electrochemical performance and exhibited superior battery-type behaviors. The results highlight that the optimized 3D-Bi₂S₃@2D-g-C₃N₄ composite sample exhibits a high areal capacity of 41.53 μA h/cm² at 1 mA/cm² and a good rate capability of 62.77% along with a remarkable capacity retention of 94.86% after 5000 cycles. The improved performance can be attributed to the good beneficial features of the synergistic effect, mesoporous structure, and lower dissolution. It offers a higher specific surface area, enriches electroactive sites, increases electronic/ionic conductivities, and reduces the interfacial resistance. Furthermore, the solid-state symmetric supercapacitors (SSCs) were assembled by two similar electrodes of 3D-Bi₂S₃@2D-g-C₃N₄ sandwiched between the KOH and PVA gel electrolyte. The fabricated SSC device provides a high areal capacity of 25.40 μA h/cm² at 1 mA/cm². Furthermore, the SSC delivers a maximum power density of 1495 μW/cm² and an energy density of 3.17 μW h/cm² with a good cyclic retention of 83.84% after 7500 cycles. This work also demonstrates the practical applicability of realizing red-light-emitting diodes by interconnecting two SSCs in series.