The effects of deposition time and current density on the electrochemical performance of flexible and high-performance MnO2@PFG composite electrodes

Abstract

A novel composite electrode has been fabricated by the direct deposition of MnO₂ onto graphene networks surrounding a paper fiber (PFG). The paper fiber between graphene sheets could be used as a flexible substrate for MnO₂ nanoparticles, and the microscopic morphologies and electrochemical performances of the MnO₂@PFG electrodes were tuned via regulating the deposition current densities and deposition times. 3D graphene on PFG served as a highly conductive backbone with a high surface area for the deposition of the MnO₂ nanoparticles, which provided high accessibility to electrolyte ions for shortening the diffusion paths. The MnO₂-10-600 s@PFG composite electrode achieved a maximum specific capacitance of 878.6 mF cm⁻² with an MnO₂ loading mass of 3.62 mg cm⁻² (specific capacitance of 187.7 F g⁻¹) at a current density of 0.5 mA cm⁻² in a 1 M NaSO₄ aqueous solution. Additionally, the MnO₂-10-600 s@PFG composite material with the most favorable composite ratio exhibited the highest energy density of 61.01 mW h cm⁻², maximum power density of 1249.78 mW cm⁻², excellent capacitance retention with no more than 7% capacitance loss after 10 000 cycles and good mechanical flexibility (about 91.06% of its original capacitance after 500 bending times). By combining the electric double layer capacitance of graphene networks with the pseudocapacitance of the MnO₂ nanostructures, the flexible electrode showed much enhanced electrochemical capacitance behaviors with robust tolerance to mechanical deformation; thus, it is promising for being woven into textiles for wearable electronics.