Carbon fiber mat from palm-kernel-shell lignin/polyacrylonitrile as intrinsic-doping electrode in supercapacitor

In Thailand, there is plenty of palm-kernel-shell (PKS) residue from the palm-oil industry, mostly used as a low-cost material for thermal generation. Thus, to enhance its values, hybrid-fiber precursors composed of PKS-extracted lignin (PKS-lignin) and polyacrylonitrile (PAN) were utilized for carbon fiber (CF) production. PKS-lignin and PAN blends in dimethyl formamide (DMF) solutions were prepared at different PKS-lignin:PAN ratios for fiber formation via an electrospinning. The fiber fabrics from the PKS-lignin:PAN ratio of 10:6 parts per hundred volume (phv) were thermal stabilized without any crosslinking agent and carbonized at 900, 1000, and 1200 °C with no physical/chemical activation. The fiber diameter of PKS-lignin/PAN CF mats was in the range of 0.3–1.1 μm with high surface area of 577–1330 m2 g−1, micropore volume (Vmicro) of 0.97–2.94 cm3 g−1, and total pore volume (Vtotal) of 1.03–2.97 cm3 g−1. Moreover, they also possessed high electrical conductivity of 20–106 S cm−1 and total heteroatom (nitrogen (N) and oxygen (O)) content of 20–24 wt%. The PKS-lignin/PAN CF fabric was directly used as a free-standing electrode material without any conductive additive/binder for electrochemical measurement. The PKS-lignin/PAN CF electrode prepared at 1000 °C exhibited the highest specific capacitance (Cs) and energy and power densities of ≅ 148 F g−1, 35 W h kg−1, and 860 W kg−1, respectively. In addition, the capacitance retention (CR) of this PKS-lignin/PAN CF electrode remained approximately 90% over 10,000 cycles. In this work, the enrichment of heteroatoms together with excellent-wetting surfaces of the PKS-lignin/PAN CF electrode played a significant role on high capacitive performances.