Enhancing the energy density of phosphorus doped mesoporous carbon nitride using redox mediated gel-polymer electrolyte

The practical application of supercapacitors is often limited by their low energy density, which stems from restricted voltage windows and insufficient redox reactions. Here, a symmetric supercapacitor device combining phosphorus-doped mesoporous graphitic carbon nitride (P-Mg-CN) electrodes with a redox-mediated gel polymer electrolyte (R-mgpe) is developed. In a three-electrode configuration, P-Mg-CN exhibited a specific capacitance of 134 F g^-1 in 1 M H₂SO₄, which increased to 398 and 207 F g^-1 in hydroquinone-based redox electrolytes, respectively, respectively, due to additional faradaic contributions from the I^-/I₃ ^- and hydroquinone/benzoquinone (HQ/BQ) redox couples. The device exhibits a broad voltage window of 1.4 V and achieves a high specific capacitance of 142 F g^-1 at a current density of 2 A g^-1. It also delivers an energy density of 38.66 Wh kg^-1 at a power density of 2.8 kW kg^-1. Furthermore, it retains 95.89% of its initial capacitance after 10 000 cycles. These results demonstrate that integrating redox-mediated gel electrolytes with heteroatom-doped carbon nitrides effectively increases the energy density of symmetric supercapacitors while maintaining long-term stability.