Ultra-long life nickel nanowires@nickel-cobalt hydroxide nanoarrays composite pseudocapacitive electrode: Construction and activation mechanism

A three dimensional hierarchical composite electrode composed of nickel nanowires@nickel-cobalt double hydroxide aligned on nickel foam is successfully fabricated by an in-situ growth route. In this composite electrode, the nickel nanowires are used as core materials to support high-pseudocapacitance nickel-cobalt double hydroxide and construct the typical Ni nanowires core@Ni-Co double hydroxide shell hierarchical structure on Ni foam. Compared with Ni-Co double hydroxide/Ni foam electrode (without nickel nanowires), the electrochemical performance of the obtained composite electrode is apparently improved, which shows a high areal specific capacitance (2.25 F cm−2 at 5 mA cm−2), excellent rate capability (1.65 F cm−2 at 100 mA cm−2) and superior cycle stability (151.2% retained in the 20000th cycle). And the activation mechanism of ultra-long cycle life of the obtained composite electrode is studied in this work, which indicates that the transforms of surface atoms on Ni nanowires into high-pseudocapacitance Ni(OH)2 and NiOOH during cycles make major contributions for the performance improvement.