Growth of NiFe2O4 nanoparticles on carbon cloth for high performance flexible supercapacitors

Abstract

In this paper, we report that NiFe₂O₄ nanoparticles can be directly grown on a flexible carbon cloth substrate by a facile surfactant-assisted hydrothermal method. The produced carbon cloth/NiFe₂O₄ (CC/NiFe₂O₄) electrodes with a loading density of 1.55 mg cm⁻² exhibited excellent electrochemical performances in both 6 M KOH and 1 M H₂SO₄ aqueous electrolytes in a two-electrode system. The carbon cloth substrate provided the conductive three-dimensional network, efficient ion diffusion path, and high surface area for NiFe₂O₄ nanoparticles, resulting in the enhancement in the specific capacitances of CC/NiFe₂O₄. The specific capacitances of CC/NiFe₂O₄ (based on the mass of NiFe₂O₄) were as high as 1135.5 F g⁻¹ (in H₂SO₄) and 922.6 F g⁻¹ (in KOH) at a current density of 2 mA cm⁻². After the current density was increased to 100 mA cm⁻², the rate retentions in both electrolytes were greater than 80%, which exceeded most of the reported electrode materials. The assembled all-solid-state symmetric supercapacitor cell showed a voltage window of 2 V using poly(vinyl alcohol) (PVA)–H₂SO₄ as the gel electrolyte, offering a high energy density of 2.07 mW h cm⁻³ at a current density of 2 mA cm⁻². These remarkable results have demonstrated that the CC/NiFe₂O₄ electrodes may provide us a new opportunity for designing high performance flexible supercapacitors.