Highly Stable Supercapacitor Devices Based on Three-Dimensional Bioderived Carbon Encapsulated g-C₃N₄ Nanosheets

Owing to the increasing demand for sustainable and eco-friendly energy storage devices such as supercapacitors, it is vital to continuously search for highly stable and cost-effective electrode materials with high energy and power densities. Herein, a 3D/2D metal-free mesoporous composite of graphitic carbon nitride (GCN) and bioderived carbon (Bio-C_<i>x</i>) is investigated as an energy storage electrode material. This composite overcomes the low conductivity and low capacitance limitations of GCN while enjoying its high corrosion resistance, high nitrogen content, and unique 2D structure. The GCN/Bio-C_<i>x</i> composite exhibits a fairly wide operating potential window of 1.2 V in 0.5 M H₂SO₄ aqueous electrolyte with a high capacitance of 300 F/g at 1 A/g. This high performance was ascribed to the huge number of available active sites, large surface area, and the unique 3<i>D</i>/2D structure. The assembled device employing the GCN/Bio-C_<i>x</i> composite as the positive electrode and mesoporous nitrogen-doped carbon (MPNDC) as the negative electrode showed an ultrahigh-energy density of 53.72 Wh/kg and a power density of 900 W/kg. The GCN/Bio-C_<i>x</i>//MPNDC device retains ∼100% of its initial capacitance after 13 000 charge/discharge cycles with 100% Columbic efficiency.