Nickel–cobalt bimetallic tungstate decorated 3D hierarchical porous carbon derived from lignin for high-performance supercapacitor applications

Abstract

Transition-metal tungstates (MWO₄), which are high-performance electrode materials for supercapacitor use thanks to their intrinsically outstanding electrochemical properties, have recently emerged and drawn great attention. Herein, we synthesized materials consisting of bimetallic Ni_4−xCo_xWO₄ (x = 0.5, 1, 1.5, 2) nanoparticles supported on enzymatic-hydrolysis-lignin-derived three-dimensional hierarchical porous carbon (Ni_4−xCo_xWO₄/HPC) and explored their usage as positive electrode materials for use in asymmetric supercapacitors. The Co/Ni ratio has a significant impact on the specific capacitance of the Ni_4−xCo_xWO₄/HPC electrode, and the Ni₃Co₁WO₄/HPC electrode, which is the best performer among Ni_4−xCo_xWO₄/HPC electrodes to the best of our knowledge, exhibits an optimal specific capacitance of 1084 F g⁻¹ (364.5 C g⁻¹) at a current density of 0.5 A g⁻¹ in 6 M KOH electrolyte solution. This is attributed to the distinctive nanostructure and strong synergistic effects between nickel and cobalt ions. Our density functional theory (DFT) calculations demonstrate that the significant capacitance enhancement seen for Ni_4−xCo_xWO₄/HPC is associated with enhanced conductivity. An assembled asymmetric supercapacitor based on Ni₃Co₁WO₄/HPC can provide a high voltage of 1.6 V and deliver an excellent energy density of 105.6 W h kg⁻¹ at a power density of 400.5 W kg⁻¹, and it has excellent stability, showing 80.74% capacitance retention after 10 000 cycles; this compares favorably with analogous supercapacitors. It is anticipated that the rational design of Ni₃Co₁WO₄/HPC will provide new paths for the synthesis of high-performance bimetallic oxide materials for application in energy-related fields.