2, Wuhan University, Wuhan, , China
Supercapacitor (SC) is emerging as an ideal energy storage device for portable electronics, electric vehicles and other high-power applications, due to its high power density, rapid charge-discharge capability, long life span and safety. As a key component of the SC, the electrode material mainly determines its overall performance. It is well-known that carbon materials are the most commonly used electrode materials for their low cost, chemical stability, open porosity and environmental friendliness. Among numerous carbon allotropes, three-dimensional (3D) porous graphitic carbon shows an outstanding advantage of combining good conductivity and porous structure. The interconnected porous networks can not only decrease the ion transport resistance and diffusion distances, but also offer larger accessible surface areas; while the graphitic carbon ensures good conductivity.
Recently, renewable biomass carbon materials have drawn great attentions as promising electrode materials for SCs. Among them, bamboo is a widely grown and multifunctional plant, which has a rapid growth rate, short maturation cycle and high yield. Due to its well-connected microtexture and multichannel structure, natural bamboo can effectively absorb and transport ions (Na+, K+), water molecules for its metabolism; meanwhile it also possesses excellent flexibility and mechanical durability. Thus bamboo could be carbonized to synthesize biomass carbon with interconnected, multichannel and porous structures, which could facilitate the ion transport as well as electrolyte penetration and enhance the energy storage capability.
In this work, we established a one-step strategy, utilizing potassium ferrate (K2FeO4), to fulfil the synchronous carbonization and graphitization of bamboo char for preparing porous graphitic biomass carbon (PGBC). Here K2FeO4 was utilized as both activating agent (KOH) and catalyst (Fe) to convert the bamboo precursor into PGBC. Without the addition of any toxic substances, the whole process is simple, safe and pollution-free. The as-prepared PGBC sample possessed a porous structure with large specific surface area (1732 m2/g) and abundant micropores, as well as a high graphitization degree. Further electrochemical measurements revealed that the PGBC electrode exhibited a high specific capacitance of 222.0 F/g at 0.5 A/g, and the solid-state symmetric SC in aqueous electrolyte (KOH/PVA) presented a considerable synergetic energy-power output property as energy density of 6.68 Wh/kg at the power density of 100.2 W/kg and 3.33 Wh/kg at 10 kW/kg. Moreover, the coin-type symmetric SC in ionic liquid electrolyte (EMIM TFSI) delivered a higher energy density of 20.6 Wh/kg at the power density of 12 kW/kg. This approach holds great promise to achieve the low-cost, green and industrial-grade production of renewable biomass-derived carbon materials for advanced energy storage applications in future.