Preparation of lignin-based porous carbon with hierarchical oxygen-enriched structure for high-performance supercapacitors.

The biomass-based porous carbon produced by the conventional two-step method (carbonization followed by chemical activation) has a high production cost and an undeveloped mesopore/macropore structure. In this study, lignin was successfully converted into porous carbon (LPC) in one step by microwave heating combined with the use of humidified nitrogen. The obtained LPC had abundant micropores (0.70 cm-3·g-1), hierarchical pore distribution (mesopore ratio: 65.8%), and an oxygen-enriched chemical structure (surface oxygen content: 16.5%). These characteristics provided a high energy density (23.0 kW·kg-1 at 10 A·g-1) and excellent rate capability of the prepared supercapacitor in a gel electrolyte (polyvinyl alcohol/LiCl), leading to a high specific capacitance of 173 F·g-1 at 0.5 A·g-1, and 71.1% at 10 A·g-1 remains. The prepared supercapacitor could deliver a high power density of 1.1 kW·kg-1 at the maximum energy density. The obtained results demonstrate the feasibility of the proposed energy-saving cost-effective preparation approach to obtain a high-performance supercapacitor with a low production cost.