Graphite‐Aligned Ni/Ni(OH)2 Nanowire‐Based Aqueous Asymmetric Supercapacitors Exhibiting Excellent Cycle Stability, High Rate Performance, and Wide Operation Voltage.

We present a new design for an asymmetric supercapacitor combining a vertically aligned Ni/Ni(OH)2 nanowire array electrode and a graphite‐based electrode. The arrangement of these two electrodes in a sandwiched fashion allows the device to function at a high operating voltage window of 2.0 V in an aqueous electrolyte. A thin layer of Ni(OH)2 can be readily formed on Ni nanowires (NiNWs) to yield a Ni/Ni(OH)2 structure. The redox reaction of Ni(OH)2 formed on the surface of NiNWs was crucial in achieving improved capacitance over this wide voltage window. The modification of the graphite electrode using graphene flakes was found to provide a more stable response at high current densities. The shape of the voltammogram can be retained up to high values and thus the device can operate at very rapid charge/discharge rates at an enhanced voltage window. Furthermore, the capacitance was found to be unchanged after 10000 continuous potential cycles. [ABSTRACT FROM AUTHOR]