Direct Growth of NiCo2S4Nanotube Arrays on Nickel Foam as High-Performance Binder-Free Electrodes for Supercapacitors

NiCo 2 S 4 nanotube arrays are grown by a two‐step hydrothermal process involving the loading of HCl cleaned Ni foam with precursors CoCl 2 and NiCl 2 (autoclave, 100 °C, 8 h) followed by adding the precursor foam to an aqueous Na 2 S solution (autoclave, 120 °C, 4 h).