Heterogeneous NiCo2O4@polypyrrole core/sheath nanowire arrays on Ni foam for high performance supercapacitors

A novel heterogeneous NiCo2O4@PPy core/sheath nanowire arrays are directly grown on Ni foam involving three facile steps, hydrothermal synthesis and calcination of NiCo2O4 nanowire arrays and subsequent in-situ oxidative polymerization of polypyrrole (PPy). When investigated as binder- and conductive additive-free electrodes for supercapacitors (SCs) in 6 M KOH, the NiCo2O4@PPy core/sheath nanowire arrays exhibit high areal capacitance of 3.49 F cm−2 at a discharge current density of 5 mA cm−2, which is almost 1.5 times as much as the pristine NiCo2O4 (2.30 F cm−2). More importantly, it can remain 3.31 F cm−2 (94.8% retention) after 5000 cycles. The as-obtained electrode also displays excellent rate capability, whose areal capacitance can still remain 2.79 F cm−2 while the discharge current density is increased to 50 mA cm−2. The remarkable electrochemical performance is mainly attributed to the unique heterogeneous core/sheath nanowire-array architectures.