In-situ growth of polypyrrole onto bamboo cellulose-derived compressible carbon aerogels for high performance supercapacitors

Highlights: • Self-supported, mechanically-robust, and compressible carbon nanofiber networks. • Low-cost electrode materials from sustainable bamboo cellulose nanofibers. • In-situ polymerization of pyrrole to produce core-sheath nanostructured composites. • Combination of high energy, high power and rate capability. -- Abstract: Carbon aerogels are suffering from moderate specific capacitance and inferior energy density for the as-fabricated electric double-layer capacitors. Meanwhile, such aerogels are limited by mechanical brittleness and traditional process of high-cost templates and unsustainable precursors. Herein mechanically-robust and compressible carbon aerogels were readily fabricated by low-temperature lyophilization of the frozen aqueous suspension of bamboo cellulose nanofibers in liquid nitrogen followed by high-temperature pyrolysis. Free-standing carbon aerogels were further coated through in-situ oxidative polymerization of pyrrole, producing homogeneous core-sheath carbon aerogel/polypyrrole (PPy@CA) composites. The symmetrical supercapacitor using the PPy@CA electrodes delivers a specific capacitance of 268.5 F g⁻¹ at 0.5 A g⁻¹ and an energy density of 23.8 Wh Kg⁻¹ at the power density of 450.4 W kg⁻¹. At an elevated current density of 10 A g⁻¹, the energy density remains as high as 19.6 Wh kg⁻¹ at the highest power density of 8018.2 W kg⁻¹. Moreover, the supercapacitor retains 88% of its initial capacitance after running 10,000 cycles at 10 A g⁻¹. These excellent performances for PPy@CA are attributable to their electrically-conductive 3D carbon frameworks and interconnective porous channels capable of efficient diffusion of electrolyte ions, fast transport of electrons, and preserving structural stability. Such active nanocomposites are currently pursued as supercapacitor electrodes due to the synergistic effect between high power density of CAs and high energy density of pseudo-capacitive PPy.