Biomolecule-assisted hydrothermal approach towards synthesis of ultra-thin nanoporous α-Co(OH)2 mesocrystal nanosheets for electrochemical capacitors

Abstract

We describe here a novel biomolecule-assisted hydrothermal strategy for the synthesis of two-dimensional ultra-thin α-Co(OH)₂ mesocrystal nanosheets. These unique ultra-thin α-Co(OH)₂ mesocrystal nanosheets have good electrical conductivity and are highly attractive for application in electrochemical capacitors due to many of their properties, such as high crystallinity with small particle size, large specific surface area, high porosity as well as good handling. Impressively, a specific capacitance (SC) of 506 F g⁻¹ can be achieved by the nanoporous α-Co(OH)₂ mesocrystals at 10 mA cm⁻² (ca. 1.33 A g⁻¹), and even 427 F g⁻¹ at 40 mA cm⁻² (ca. 5.33 A g⁻¹), indicating their great ability to deliver a large SC and high electrochemical utilization at high rates. Moreover, a low SC degradation of ca. 3% after 2000 continuous charge–discharge cycles at a current density of 5.33 A g⁻¹ reveals their good electrochemical stability at high rates, which is of great importance for their practical application. The synthesis strategy reported here is a simple and cost-effective means of performing the large-scale production of α-Co(OH)₂ mesocrystal nanosheets with good electrochemical capacitance, and is expected to be applied in the preparation of other metal hydroxides or oxides with similar microstructures and electrochemical properties for use in electrochemical capacitors or even for use in Li-ion batteries.