Electrochemical performance of cobalt hydroxide nanosheets formed by the delamination of layered cobalt hydroxide in water

Abstract

We report the preparation of monometallic Co(2+)/Co(3+) layered double hydroxide, intercalated with lactate anions (LCoH-Lactate), and its spontaneous delamination in water to form cobalt hydroxide nanosheets. These hydroxide nanosheets formed stable aqueous dispersions. The thickness of a nanosheet was estimated to be approximately 1 nm by atomic force microscopy and small angle X-ray scattering experiments, and corresponds to a single hydroxide layer. Some of the Co(2+) cations were oxidised by oxygen, resulting in a mixed Co(2+)(0.76)Co(3+)(0.24) layer composition. Upon water evaporation, the nanosheets restacked to form transparent self-standing films with a layered structure like that of the original material. The coverage of the surface with side-by-side stacks of nanosheets indicated two-dimensional agglomeration and suggested that these dispersions could be applied to prepare large monolayers of nanosheets. The layers prepared by spin-coating were stable and featured reversible and reproducible redox properties in an alkaline electrolyte. In an evaluation of their electrochemical performance, the cobalt hydroxide nanosheets exhibited durability and fast charge transfer kinetics during repetitive potential cycling up to 200 mV s(-1). The nanosheets prepared by the present method show promise for use in nanocomposite materials for energy storage applications.