Integrated hybrid architecture of metal and biochar for high performance asymmetric supercapacitors

Two state-of-the-art electrodes were successfully synthesized and used to assemble both symmetric and asymmetric type supercapacitors. 3DFAB was fabricated by direct pyrolysis of green macroalgae in the presence of NaOH. Possible NaOH activation mechanisms are proposed, which explains the formation of oxygen functional groups through quick penetration of OH- and NaOH into the vacancies. To obtain CoTLM, the tile-like architecture of cobalt oxides was introduced to the 3D interconnected functional algal biochar (3DFAB) by a simple one-pot hydrothermal method under mild conditions. For the symmetric supercapacitors, the maximum specific capacitance of RAB, 3DFAB, and CoTLM were 158, 296, and 445 F g^-1 at the current density of 1 A g^-1. Regarding cobalt-based asymmetric systems, the maximum capacitance for the 3DFAB//CoTLM was 411 F g^-1. This asymmetric supercapacitor device also retained 100.9% of its initial capacitance after 4000 cycles at the current density of 4 A g^-1. Unbuffered aqueous electrolyte and the unique morphological structure used in this study might catapult forward commercialization of such advanced energy storage devices.