Enhanced Performance of Nickel-Doped Porous Carbon Derived from Soybean Hulls for Supercapacitor Applications

Abstract

Bio-based activated carbon and transition metal oxides, as electrode materials, possess excellent electrochemical performance and have broad prospects for application in supercapacitor devices. Soybean husks are a renewable, inexpensive, and widely utilized biomass waste, making them an ideal choice for biomass-activated carbon. Nickel can undergo reversible multivalent state transformation (such as Ni2+/Ni3+/Ni4+) in redox reactions and has high electrochemical activity. In this study, Ni(NO3)2·6H2O was used as the nickel source and loaded onto soybean hulls (SBH) activated by K2CO3 to prepare SBH@Ni-x. The composite material achieved a maximum specific capacitance of 513.9 F·g-1 at 1 A·g-1 during the three-electrode test with 6 M KOH. When forming symmetrical SCs with SBH@Ni-0.05//SBH@Ni-0.05, the energy density in 1 M Na2SO4 electrolyte reaches 28.35 Wh kg-1, whereas in 6 M KOH electrolyte it remains at 14.24 Wh kg-1 (1 A·g-1). Additionally, after 10,000 cycles, it retains 83.3% of its original capacitance and has a Coulombic efficiency of nearly 100%. These results indicate that Nickel loaded on biomass-activated carbon is a promising continuous, efficient, and eco-friendly material for supercapacitor devices.