Green Approach for Synthesizing Three Different Carbon Microstructures from a Single Biowaste Bombax malabaricum for Fully Biocompatible Flexible Supercapacitors and Their Performance in Various Electrolytes

The scalable design and inexpensive synthesis of high-surface-area conductive porous carbon electrode materials for high-performance supercapacitors have found extensive interest. Typically, the inherent structure and composition of the biomass or biowaste influence the final structural and morphological properties of carbon nanomaterials. To investigate the influence of internal microstructure on the final products and their effect on electrochemical performance, herein, for the first time, we demonstrated a facile approach for the synthesis of three unique microstructures. N-doped two-dimensional wrinkled few-layered porous graphene nanosheets (N-HGNSs), three-dimensional honeycomb-like porous carbon (N-HPC), and carbon microflakes (N-CMF) are synthesized from three different parts of a single biowaste material, Bombax malabaricum. N-HGNS, N-HPC, and N-CMF electrode materials exhibit high specific capacitance (Cp) values of 523, 458, and 363 F g–1, respectively, at a high current density of 1.5 A g–1 in 1 M H2SO4 with a high rate capability of ∼82% at 30 A g–1, which are, to the best of our knowledge, among the highest ever testified for N-doped carbon materials obtained from biowaste. Furthermore, a fully biocompatible flexible solid-state supercapacitor device is successfully designed with high energy densities of 19.4 and 17.84 Wh kg–1, as well as excellent energy densities of 76.9 and 53 Wh kg–1 are presented in Na2SO4 electrolyte for N-HGNS and N-HPC electrodes, respectively. It is believed that this single-step novel green approach could aid in the design of an efficient and large-scale process to prepare electrode materials with tunable properties from biowaste for excellent energy storage applications. Furthermore, the three flexible supercapacitors connected in series can power a red light-emitting diode for 20 and 15 min after charging for 60 s for N-HGNS and N-HPC, respectively