Heteroatoms co-doped multi-level porous carbon as electrode material for supercapacitors with ultra-long cycle life and high energy density

As a promising electrode material for supercapacitors, porous carbon has received widespread attention. However, taking into account of the capacitive performance, the cost and environmental protection, the practicability of the carbon previously reported is still unsatisfactory. Therefore, it is meaningful and challenging to develop a proper carbon material. In the present work, N, O, P co-doped porous carbon materials are prepared from poplar catkin biomass wastes with a two-step chemical activation method by using H3PO4 and K2CO3, separately. Specifically, the optimal HKPC-1-2.0 possesses a multi-level pore structure with an ultra-high specific surface area (2133 m2 g-1) and a suitable micropore percentage (52.8 %). As a result, HKPC-1-2.0 displays a specific capacitance of 296.2 F g-1 at 1.0 A g-1 in the three-electrode system by using 6.0 M KOH as electrolyte. More importantly, the symmetrical HKPC-1-2.0//HKPC-1-2.0 device exhibits a high capacity retention rate of 100.1 % even after 40,000 charge-discharge cycles at 1.0 A g-1. The co-doping of the heteroatoms and the hierarchical network with suitable pore size distribution are advantageous for the storage and transportation of ions, therefore leading to the encouraging capacitive performance. This work not only offers a low-cost and high performance carbon electrode material for supercapacitors but also develops an environmentally-friendly strategy for effectively conversing biomass wastes to high value-added products.