Boosting the crystallinity of novel two-dimensional hexamine dipyrazino quinoxaline-based covalent organic frameworks for electrical double-layer supercapacitors

Supercapacitors (SCs) are strong candidates for electrical energy storage. However, their widespread use is limited by their low energy storage density and relatively high effective series resistance. Designing superior electrode materials is critical to advancing the energy density without losing stability and power density. Covalent organic frameworks (COFs) have enormous potential in this area, although preparing COFs for high-performance SCs remains a challenge. A novel and conjugated 2D 250-HADQ COF has a highly crystalline two-dimensional network obtained by optimizing the reaction conditions to achieve a 1 nanometer-width pore with a nitrogen content of around 37%, exhibiting a high specific surface area of 2443 m² g⁻¹ and excellent thermal stability (up to 1000 °C). Two-electrode double-layer supercapacitor cells fabricated with this 2D material yielded high values of gravimetric capacitance (516.4 F g⁻¹ at 0.5 A g⁻¹) and energy density (219.4 W h kg⁻¹ at 437.5 W kg⁻¹ power density) and achieved a capacity retention of 81% at a current density of 2 A g⁻¹ after 100 000 charge-discharge cycles with an ionic liquid electrolyte. This work provides an excellent active material for supercapacitors, highlights the association between the structure of electrode materials and supercapacitors' performance, and improves the application of COFs in SCs.