Hydrangea-like N/O codoped porous carbons for high-energy supercapacitors

Carbons with specific morphologies, compositions and structures have aroused scientific and technological interest due to their intriguing and overwhelming properties for multi-purpose applications. Herein, a novel route to convert Knoevenagel copolymer into hydrangea-like, N/O codoped, and high-surface-area porous carbon (HPC) spheres with excellent supercapacitive performances is presented. By crosslinking p-phenylenediacetonitrile with two aromatic aldehyde co-monomers, as-prepared material exhibits a unique architecture of intertwined nanosheets uniformly self-assembled on the surfaces of microporous spheres. Featuring a large adsorbing platform (1963 m2 g−1), multi-scale pore structure and diverse N/O functional groups, HPC electrode carbonized-activated at the optimal temperature of 700 °C yields a prominent capacitance of 330 F g−1 at 1 A g−1, along with a satisfactory rate capability of 221 F g−1 at 20 A g−1 in KOH electrolyte. More importantly, taking advantage of a refined interphase between the high-concentration water-in-salt Li-TFSI layer and the ion-accessible hydrangea surface, HPC-based supercapacitor gives a higher energy delivery of 32.9 Wh kg−1 at 575 W kg−1 than the common devices using KOH (10.93 Wh kg−1 at 100 W kg−1) and Na2SO4 (24.9 Wh kg−1 at 180 W kg−1), with high-voltage aqueous durability of 90.5% retention over 10,000 cycles at 2.3 V. This inspiring work enriches the methodology for fabricating functionalized carbon spheres that are expected to boom diverse applications.