Rapid in situ growth of β-Ni(OH) nanosheet arrays on nickel foam as an integrated electrode for supercapacitors exhibiting high energy density.

Ni(OH)2 has been widely investigated as a prospective electrode material because of its high theoretical capacitance and relatively low cost. However its synthesis usually needs a complex and lengthy process, and a binder is generally used for fabricating Ni(OH)2 based electrodes. In this work, a self-supporting binder-free β-Ni(OH)2@nickel foam (NF) integrated electrode was prepared by the in situ growth of β-Ni(OH)2 on NF using a rapid and facile approach. This approach consists of two processing steps: (1) the pre-treatment of NF with an acid and (2) the quick in situ electrochemical synthesis of β-Ni(OH)2 on the NF in the KOH electrolyte within half a minute under an applied voltage. The β-Ni(OH)2@NF integrated electrode possesses a three-dimensional network structure of nanosheet arrays and exhibits excellent electrochemical performance. Its areal capacity is 3.68 mA h cm-2 at a current density of 2 mA cm-2, and the capacity can retain 115.8% of its initial value even after 2000 cycles at a current density of 15 mA cm-2. Moreover, the as-assembled β-Ni(OH)2@NF//activated carbon (AC) asymmetric supercapacitor (ASC) exhibits a high energy density of 74.2 W h kg-1 with a power density of 776.9 W kg-1 and excellent cycling stability (89.9% retained after 10 000 cycles). This work provides an efficient, facile and economic method for fabricating Ni(OH)2 based integrated electrodes for high-performance supercapacitors.