Mixed valence Zn–Co-layered double hydroxides and their exfoliated nanosheets with electrode functionality

Abstract

New phases of Zn-Co-layered double hydroxides (Zn-Co-LDHs) were synthesized for the first time via a co-precipitation reaction using hydrogen peroxide as an oxidant. According to powder X-ray diffraction and field emission-scanning electron microscopy, both nitrate-and sulfate-forms of the Zn-Co-LDHs crystallized with the brucite-type layer structure having interlayer nitrate and sulfate anions, respectively, and commonly showed plate-like morphology with a crystal size of several hundred nanometers. dc magnetic susceptibility measurements revealed that the Zn-Co-LDHs displayed ferromagnetic/antiferromagnetic transitions below 15 K and the magnetic moment calculated from the paramagnetic region (30-300 K) indicated the co-existence of weak field Co 2+ and strong field Co 3+ ions. The mixed oxidation state of Co 2+ /Co 3+ was confirmed by the results of iodometry and X-ray absorption near-edge structure spectroscopy. The heat-treatment for the Zn-Co-LDHs at elevated temperatures produced mixed metal oxide nanocomposites composed of spinel ZnCo 2 O 4 and wurzite ZnO phases. The colloidal suspension of exfoliated Zn-Co-LDH nanosheets could be synthesized by dispersion of the pristine LDH materials in formamide, which was confirmed by the Tyndall phenomenon, high resolution-transmission electron microscopy/selected area electron diffraction, and UV-vis spectroscopy. The Zn-Co-LDH film fabricated with the restacked nanosheets exhibited pseudocapacitive behavior with a large specific capacitance and a good capacitance retention. The present findings underscore that the newly synthesized mixed valence Zn-Co-LDH phases showed promising functionality as a supercapacitor electrode material and also showed interesting magnetic coupling behavior.

LDHs as Electrode Materials for Electrochemical Detection and Energy Storage: Supercapacitor, Battery and (Bio)-Sensor

“…Finally an interesting other approach to yield highly exposed materials is the single platelets formation. Inspired by the work of Sasaki et al [6], exfoliated ZnCo-LDH nanosheets are synthesized by dispersion of the pristine LDH materials in formamide [143]. Subsequently the ZnCo-LDH film is fabricated from the restacked nanosheets and it exhibits pseudocapacitive behavior with a large specific capacitance and good capacitance retention.…”

Exfoliation-restacking synthesis of coal-layered double hydroxide nanosheets/reduced graphene oxide composite for high performance supercapacitors

“…The mass loss between 200-400 °C can be assigned to the removal of nitrate anions between the layers and the de-hydroxylation of CAN-LDH. For pure CAN-LDH, there is no notable change in mass after 400 °C, indicating the completion transformation of the CAN-LDH to corresponding metal oxide [42]. The composites present an additional weight loss between 700-900 °C, which is attributed to the removal of the residual oxygen-containing groups in rGO [43].…”

Recent Advances of Two‐Dimensional Nanomaterials for Electrochemical Capacitors

“…adopted hydrogen peroxide as an oxidantt os ynthesize layered brucite-typeZ n ÀCo LDHs throughacoprecipitation reaction. [66] The as-prepared ZnÀCo LDH materials showed not only interesting magnetic properties, but also pseudocapacitance behavior. Analogously,L u et al prepared CoÀCu LDH stacked nanosheets with at hickness of 4.3 nm through the coprecipitation methodu nder Ar gas through ap referentially oriented growth mechanism ( Figure 8).…”

“…[67] Copyright 2019, Wiley-VCH.SICs:Reproducedw ith permission. [66] Copyright 2019,W iley-VCH. below 1nmw ere also synthesized through the molecular selfassembly mechanism.…”