Multifunctional Template Prepares N-, O-, and S-Codoped Mesoporous 3D Hollow Nanocage Biochar with a Multilayer Wall Structure for Aqueous High-Performance Supercapacitors

To recycle wastes and develop renewable energy, much effort has been focused on converting biowastes into porous carbon for supercapacitors. Porous nanocage-like carbons have excellent capacitive properties, but generally their preparation methods are costly or complex. Herein, a “one-step” strategy of synchronous activation and support through the thermal decomposition of a multifunctional template (magnesium acetate, Mg(Ac) 2 ) is designed to prepare N-, O-, and S-codoped mesoporous hollow biochar nanocages (BNC-700). The BNC-700 prepared displays an interconnected porous structure and a two-dimensional (2D) multilayer wall/three-dimensional (3D) hollow nanocage structure with abundant active heteroatoms and edge defects. Due to their specific structures, high surface areas (1369 m 2 g –1 ), and large pore volumes (1.81 cm 3 g –1 ), the assembled supercapacitor delivers a considerable energy density of 37.4 Wh kg –1 at 212 W kg –1 and cycling stability of 99.5% after 15,000 cycles. The unique structure and N, O, and S codoping characteristics ensure a potential application for BNC-700 in supercapacitors. In summary, a strategy is designed for the green, simple, and cost-effective preparation of high-performance biochar for advanced energy storage devices.