No abstract

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 mechanisms of NaOH activation is 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 177 F g− 1, 322 F g− 1, and 529 F g− 1 at a scan rate of 5mVs− 1. Regarding cobalt-based asymmetric systems, the maximum capacitance for the RAB//CoTLM and 3DFAB//CoTLM were ∼300 F g− 1 and 400 F g− 1, respectively. The 3DFAB//CoTLM showed a higher energy density compared with RAB//CoTLM, while the RAB//CoTLM exhibited better cycling performance (99.1% of its initial capacitance after 4 k cycles at the current density of 4 A g 1).