Porous NiCo2O4-reduced graphene oxide (rGO) composite with superior capacitance retention for supercapacitors

•A porous NiCo2O4-rGO network was directly deposited on nickel foam using a simple and green technique.•The rGO had a larger specific surface area and improved the conductivity of NiCo2O4.•The technique can protect the substrate from corrosion, making the quantity of the synthesized material more accurate and controllable.•NiCo2O4-rGO exhibited a specific capacitance of 777.1 F g−1 at 5 A g−1 and retained about 99.3% of the capacitance after 3000 cycles.

In present work, we developed a simple and green route to fabricate irregular porous network-like NiCo2O4-reduced graphene oxide (rGO) nanocomposite supported on the nickel foam substrates, which was directly used as a binder-free electrode for supercapacitors. The rGO served as a conductive network to facilitate the collection and transportation of electrons during the cycling, improved the conductivity of NiCo2O4, and allowed for a larger specific surface area. The irregular porous structure allowed for the easy diffusion of the electrolyte into the inner region of the electrode. Moreover, the nanocomposite directly fabricated on nickel foam with a better adhesion and avoided the use of polymer binder. This method efficiently reduced ohmic polarization and enhanced the rate capability. As a result, the NiCo2O4-rGO nanocomposite exhibited a specific capacitance of 777.1 F g−1 at 5 A g−1 and about 99.3% of the capacitance retained after 3000 cycles. The capacitance retention was about 87.6% when the current density increased from 1 A g−1 to 20 A g−1. These results indicated that such the irregular porous network-like structure directly synthesized on the substrate could be a promising candidate for high performance energy storage application.