Green Synthesis of Fe-Decorated Carbon Sphere/Nanosheet Derived from Bamboo for High-Performance Supercapacitor Application

Designing low-cost and sustainable electrode materials for energy storage devices with large energy density and capacitance is still a formidable challenge. Herein, a green, template-free, and facile Fe-decorated porous carbon synthesis strategy derived from bamboo was proposed. This strategy includes hydrothermal carbonization pretreatment, which can tune the carbon morphology and dope iron elements in one step, and a mild KHCO3 activation to improve porosity while retaining the spherical morphology. The optimized Fe-decorated porous carbon exhibited a high surface area (1509.5 m2 g–1) with a carbon sphere/nanosheet architecture, which is beneficial for ion/electrolyte diffusion and increasing the accessibility between the surface area and electrolyte ions. Moreover, the introduced Fe oxides can provide extra pseudocapacitance, which comes from the reversible faradaic reaction between Fe3+ and Fe2+. The resulting carbon material presented a high capacitance of 467 F g–1 at 0.5 A g–1. The assembled KOH-based symmetric supercapacitor displayed a superb cycling performance that can output 99.8% of the initial capacitance after 5000 cycles, and the Na2SO4-based device showed the maximum energy density of 20.31 W h kg–1. Meanwhile, different behaviors in different electrolytes were further analyzed. This work demonstrated that the modification of hydrochar is an effective way to convert biomass into high-performance electrode materials, which has potential for advanced storage device applications.