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

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.