Porous biochar derived from tea saponin for supercapacitor electrode: Effect of preparation technique

Biochar is widely employed as an electrode of supercapacitor. In this work, one-step pyrolysis and chemical activation method were introduced to prepare porous biochars from tea saponin (TS). The performance differences of biochars prepared by two methods were studied. On this basis, further researches were carried out to explore the influence of the mass ratio of KOH/pre-carbonized precursor on the structure and electrochemical performance of the biochars. All samples were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Raman spectra, Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The results revealed that KOH could effectively increase the specific surface area of biochar. The specific area of ACTS-1.0 prepared with a KOH/pre-carbonized precursor mass ratio of 1:1, is up to 1550.03 cm2/g with a pore volume of 0.9076 cm3/g, and the structure was highly amorphous and disordered. The FT-IR and XPS results showed that there are various functional groups on the ACTS-1.0 biochar surface. These structural and compositional advantages lead to a higher specific capacitance (278 F/g) of ACTS-1.0 in an aqueous electrolyte and a high energy density of 27.01 Wh/kg at an organic electrolyte. Meanwhile, the as-prepared ACTS-1.0 has excellent cycling stability over 10,000 cycles in various electrolytes.