Nanotextured alpha Ni(ii)–Co(ii) hydroxides as supercapacitive active phases

Abstract

A family of monophasic nanoplatelets of Ni(II)–Co(II) layered hydroxides, were obtained by a one-pot room temperature homogeneous alkalinization driven by the the epoxide route with glycidol. Both cations precipitate in the form of solid solutions, giving the general formula Ni_1−xCo_x(OH)_2−yCl_y·nH₂O. Co(II)-rich samples developed the simonkolleite-like alpha structure in which cations can adopt either octahedral (Oh) or tetrahedral (Td) environments, according to the formula (Ni,Co)^Oh_1−xCo^Td_2x(OH)_2−2x(Cl)_2x·nH₂O. Ni(II)-rich ones resulted in ill-crystallized turbostratic (Ni,Co)_1−x(OH)_2−x(Cl)_x·nH₂O. Despite the inherent differences in the crystallochemical nature of theses phases, electrochemical measurements depict a monotonous behavior in terms of their capacitance. An optimum performance was observed for samples with X_Ni(II) = 0.83 under most of the experimental conditions explored. This sample reaches a maximum specific capacitance of 2091 F g⁻¹, registered at a discharge current density of 0.5 A g⁻¹, while an energy density of 80.7 W h kg⁻¹ was recorded at a power density of 960.4 W kg⁻¹.