Acetamide-assisted hydrothermal growth of NiCo double hydroxide on graphene modified Ni foam for high-performance supercapacitor

Abstract

The free-standing hierarchical flower-like NiCo-double hydroxide/reduced graphene oxide composite (NiCo-DH/RGO) on Ni foam (NiF) was synthesized with a facile two-step method. First, the growth of partially reduced graphene oxide (PRGO) membrane on NiF was achieved via the direct reduction of graphene oxide (GO) by NiF, which acted as not only the reducing agent but also the current collector. Then, the growth of high mass-loading NiCo-DH on PRGO/NiF was realized with a hydrothermal process, in which acetamide plays a crucial role. The high mass-loading of NiCo-DH is due to the addition of acetamide into the hydrothermal bath, in which PRGO reacted with the solution, containing Ni(II), Co(II), acetamide and urea, to form a thick gelatinous membrane on Ni foam. During the hydrothermal process, PRGO was further reduced to RGO while both Ni(II) and Co(II) reacted with ammonium, released by the hydrolysis of urea, to form NiCo-DH. Used as the positive electrode of supercapacitor, NiCo-DH/RGO/NiF displays an ultrahigh areal capacity of 6.15 C cm−2 at 10 mA cm−2 and 94.6% capacity retention after 1000 GCD cycles at 10 mA cm−2. An asymmetric supercapacitor (ASC) is also assembled with NiCo-DH/rGO/NiF as the positive electrode and activated carbon (AC) as the negative electrode. The ASC exhibits a prominent energy density of 61.81 Wh kg−1 at a high power density of 842.63 W kg−1. It is especially worth noting that the ASC exhibited remarkable capacity retention of 84.53% even after 1000 GCD cycles at a current density of 10 mA cm−2.