Facile synthesis of Ni-Co layered double hydroxide with nitrates as interlayer anions via an oxidation-induced anion intercalation process for hybrid supercapacitors

Abstract

Ni-Co layered double hydroxide (NCLDH) with nitrate anions as interlayer counter ions was obtained via an oxidation-induced anion intercalation process. The optimization on the tunable proportion between divalent and trivalent metal cations in NCLDH host layers is realized in the dependence on the regulation of the additive amount of hydrogen peroxide as an oxidizing agent. The increase of trivalent metal cations facilitates the intercalation of nitrate anions into the interlamellar region between NCLDH host layers. Importantly, the electrostatic interaction between NCLDH host layers and interlayer anions results in the formation of hierarchical flower-like morphologies towards the enhancement of specific surface areas. Moreover, the increase in number of interlayer nitrate anions expands effectively interplanar spacing between NCLDH host layers. Remarkably, this unique structure not only accelerates the diffusion process of active hydroxide anions in the bulk phase of LDH, but also strengthens the stability of the hierarchical structure during electrochemical reactions. The electrochemical evaluation shows that NCLDH-16 achieves a superior specific capacity of 802 C g−1 at a current density of 1 A g−1 with a capacity retention of 86.7% as the increase of current densities to 10 A g−1. The NCLDH-16//AC hybrid supercapacitor delivers a maximum energy density of 37.6 Wh kg−1 at a power density of 800 W kg−1 as well as still retains 87.4% of the initial capacitance after 10 000 cycles, suggesting great potential in practical energy storage devices.