Assembly of Ni-Al layered double hydroxide and graphene electrodes for supercapacitors

Delaminated Ni-Al layered double hydroxide (LDH) was incorporated between graphene nanosheets to form a layered structure as a new generation of supercapacitor electrode material. First, Ni-Al layered double hydroxide (LDH) was grown hydrothermally, then delaminated by ultrasonication, and combined with a graphene oxide suspension prepared by a modified Hummers method. Subsequently, the graphene oxide in this mixture was reduced to graphene. It is the first time to prepare such layered hybrid structure from these two pre-prepared layered materials: graphene oxide and delaminated Ni-Al LDH in aqueous medium instead of the in-situ growth of Ni-Al LDH on graphene oxide nanosheets. Using both materials in their layered form provided more contact between electrochemically active areas which resulted in two favourable conditions to realize their electrochemical energy storage capacity: graphene has enhanced the conductivity of Ni-Al LDH and eliminated the need of conducting additives: the Ni-Al LDH has prevented the restacking of graphene sheets. The layer structured hybrid material demonstrated a superior electrochemical performance due to the synergistic effect from the pseudocapacitance of Ni-Al LDH and the electrical double layer capacitance of graphene. The graphene/Ni-Al LDH-based electrodes provided a specific capacitance of 915 F/g at a current density of 2 A/g based on the total mass of active materials in the absence of conductive additives. After 1500 cycles at a current density of 10 A/g, 95% of the initial capacitance was retained. The high electrochemical performance and facile aqueous-based synthesis route demonstrated that the G/Ni-Al LDH composite can be a promising electrode material for supercapacitor applications. (C) 2014 Elsevier Ltd. All rights reserved.