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 m2 g–1), and large pore volumes (1.81 cm3 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.