A free template strategy for the fabrication of nickel/cobalt double hydroxide microspheres with tunable nanostructure and morphology for high performance supercapacitors

Abstract

We report a free template strategy for the fabrication of nickel/cobalt double hydroxide microspheres (Ni/Co-DHMs) in a tertbutanol–water (TBA–H₂O) medium. This study demonstrates that the nanostructure and morphology of the Ni/Co-DHMs can be easily tuned by altering the ratio of TBA/H₂O. When the reaction is performed in a solvent mixture with a low water content, the as-synthesized Ni/Co-DHMs form as pure nanoflakes with a good hydrotalcite structure, but increasing the ratio of water leads first to a mixture of nanoflakes and nanorods, and then increasing it further gives rise to a mixture of pure α-Co(OH)₂ and α-Ni(OH)₂ nanorods. In this work, three typical Ni/Co-DHM materials were prepared using TBA/H₂O ratios of 9 : 1, 8 : 2 and 6 : 4. Since the unique architecture of the synthesised Ni/Co-DHM materials leads to greatly improved faradaic redox reaction and mass transfer, these Ni/Co-DHM electrodes offer high electrochemical performance for application in supercapacitors. Their specific capacities are 1800.4 F g⁻¹, 1603.2 F g⁻¹ and 1430.8 F g⁻¹ at a current density of 1 A g⁻¹, and 98.7%, 95.1% and 90.1% of these specific capacities are retained at a current density of 10 A g⁻¹ after 3000 cycles, respectively. This study also provides a promising approach for the design and synthesis of structure tunable materials with largely enhanced electrochemical characteristics, which can be potentially applied in various energy storage/conversion devices.