Hierarchical Porous Carbon and Cobalt Silicate Nanosheets Derived from Rice Husks for High-Performance Hybrid Supercapacitors: A Strategy for High-Value Utilization

Abstract

The effective utilization of agricultural waste rice husks has attracted wide attention. Herein, hierarchical porous carbon (MgPRHC) and cobalt silicate nanosheets (CSONS) are prepared using the one-to-two strategy from rice husks, with the organic biostructure and amorphous SiO₂ as precursors, respectively. Notably, the site-occupancy effect of MgO, produced from high-temperature pyrolysis of basic magnesium carbonate, effectively regulates the porous structure of MgPRHC. The specific capacitance of the MgPRHC electrode reaches 209.6 F g^-1 at a current density of 0.5 A g^-1 and maintains 95.6% after 10,000 charging/discharging cycles. Furthermore, the cobalt silicate material exhibits a two-dimensional nanosheet structure and excellent charge storage performance, which is synthesized from a 1.5 molar ratio of Co²⁺ to amorphous SiO₂ by a one-step hydrothermal reaction. Especially, the CSONS electrode exhibits the battery-type charge storage behavior, with a specific capacitance of 581.9 F g^-1 at 0.5 A g^-1. When paired with MgPRHC as the cathode, the CSONS//MgPRHC hybrid supercapacitor achieves a maximum energy density and power density of 34.8 Wh kg^-1 and 17.4 kW kg^-1, respectively. The capacitance retention retains at 96.6% after 10,000 continuous cycles of charging and discharging with minimal degradation of Coulombic efficiency. This work provides a technical route for the high-value utilization of rice husks and theoretical basis for biomass-based supercapacitors.