N-rich porous carbons with a high graphitization degree and multiscale pore network for boosting high-rate supercapacitor with ultrafast charging

An increasing energy storage property with high rate capability during fast charging at the high current density has been a long-standing challenge for supercapacitors. In this work, a novel nitrogen-enriched graphitized hierarchical porous carbon (NGHPC) was synthesized by a convenient one-step carbonization process from melamine(M)-resorcinol(R)-formaldehyde(F) co-polymeric microspheres using nano gamma-Fe2O3 as template, graphitized catalyst precursor and activation promoting agent coupled with ZnCl2 activation. The nano-sized gamma-Fe2O3 was reduced to Fe metal and other Fe-containing species in the carbonization process, and Fe served as catalyst to generate perfectly graphitized carbon skeleton, and other nanoparticles acted as the template of macropores. Meanwhile, CO2 which generated from the oxidation reactions of CO and gamma-Fe2O3 reacted with carbon to bring the in situ CO2 physical activation, resulting in the promotive tailoring in microporosity. Interestingly, the morphology of the obtaining NGHPC materials could be controlled from spherical aspect to the structure of sphere coated by thin sheet by varying the M/R mass ratio. As supercapacitor electrodes materials, the optimal material achieved an outstanding specific capacitance of 417.5 F g(-1) at 0.5 A g(-1) in 6 M KOH electrolyte. More importantly, a superb rate capability was also exhibited, and a capacitance of 296.4 F g(-1) was still retained at an ultrahigh current density of 100 A g(-1). Besides, the assembled symmetric supercapacitor with the optimal material displayed a high integrated energy density of 33.9 Wh kg(-1) at a power density of 809.9 W kg(-1) within a voltage range of 0-1.8 V in 0.5M Na2SO4 natural electrolyte and an approximate 84.8% capacitance retention after consecutive 10,000 cycles at 5 A g(-1).