Preparation of fly ash-based cobalt-iron silicate as supercapacitor electrode material

Based on the high-calcium fly ash of an actual coal-fired power plant, the crystalline silica is successfully transformed into cobalt-iron silicate, and then CNFs/FA-CoFeSiSx with good energy storage performance is obtained by modifying the cobalt-iron silicate as the electrode material of supercapacitor. The crystalline silica is successfully converted to silicate (Ca2SiO4) by high-temperature calcination with NaHCO3 and fly ash. Meanwhile, a 3D porous structure of fly ash is obtained by etching. Ion exchange is successfully carried out by the one-step hydrothermal method, which realizes the transition of Ca2SiO4 to Co2SiO4 and Fe2SiO4. The further modification through electrostatic self-assembly and sulfurization process significantly increases the electron migration rates. The situation that fly ash is difficult to be used in energy storage is ameliorated by the coordinated regulation of various strategies. The final product CNFs/FA-CoFeSiSx exhibited a high specific capacitance (493.33 F·g−1 at 0.5 A·g−1), high Coulombic efficiency (about 100% at 10 A·g−1), and good cycle performance (79.50% capacitance retention after 1800 cycles). Finally, a solid-state asymmetric supercapacitor is assembled based on CNFs/FA-CoFeSiSx as the positive electrode and commercial active carbon as the negative electrode, which performs the maximum energy density of 25.43 Wh·kg−1 and power density of 359.07 W·kg−1. Considering the good energy storage characteristics of fly ash electrode materials, this work provides a low-cost preparation method for electrochemical energy storage and realizes the high-value utilization of fly ash.