Oxalate-assisted formation mechanism of lignocellulose-based two-dimensional porous carbon and its application in zinc-ion hybrid capacitors

Oxalates are ideal additives for preparing 2D porous carbon from lignocellulose. • Oxalate-derived carbonate acts as an in situ hard template for 2D structures. • Decomposition–repolymerization behavior is the key to forming 2D porous carbon. • Oxalate-assisted formation process of lignocellulosic 2D structures is elucidated. • Prepared 2D carbon cathode shows high performance in zinc-ion hybrid capacitors. Two-dimensional (2D) carbon materials had demonstrated significant potential for various applications such as energy storage and catalysis. However, the conversion of solid lignocellulosic biomass into graphene-like 2D structures remained highly challenging, with the underlying mechanisms being poorly understood. In this work, ultrathin 2D porous carbon materials were prepared from birch biomass via a facile one-step pyrolysis process using oxalates as additives. Mechanistic studies indicate that oxalate significantly promotes the deposition and polymerization of holocellulose decomposition products, along with the release of lignin-derived phenols. This alteration in the “decomposition–repolymerization” behavior facilitates the self-assembly of reactive intermediates into 2D structures on the carbonate surfaces generated from oxalate decomposition, while the activation by alkaline metal ions within the carbonate templates effectively regulates the pore structures. When evaluated as a cathode for zinc-ion hybrid capacitors (ZIHCs), the resulting 2D porous carbon (KAC-800) delivered outstanding performance. It achieved a high specific capacity of 213.6 mAh·g −1 at 0.1 A·g −1 , a remarkable energy density of 170.56 Wh·kg −1 , excellent rate capability, and long-term cycling stability (90.6 % retention after 10,000 cycles). This study elucidates the formation mechanism of 2D porous carbon in an oxalate-mediated system at the molecular level, offering valuable insights for the rational design of high-performance biomass-based 2D carbon materials. Download: Download high-res image (204KB) Download: Download full-size image