Preparation, ion-exchange, and electrochemical behavior of Cs-type manganese oxides with a novel hexagonal-like morphology

Abstract

Cs-type layered manganese oxide with a novel hexagonal-like morphology (Cs–BirMO) was prepared by a solid-state reaction procedure. The Cs+ extraction and alkali–metal ion insertion reactions were investigated by chemical analyses, x-ray analyses, scanning electron microscopy observation, Fourier transform-infrared spectroscopy, thermogravimetric differential thermal analyses, pH titration, and distribution coefficient (Kd) measurements. A considerable percentage (88%) of Cs+ ions in the interlayer sites were topotactically extracted by acid treatment, accompanied by a slight change of the lattice parameters. Alkali–metal ions could be inserted into the interlayer of the acid-treated sample (H–BirMO), mainly by an ion-exchange mechanism. The pH titration curve of the H–BirMO sample showed a simple monobasic acid toward Li+, Rb+, and Cs+ ions, and dibasic acid behavior toward Na+ and K+ ions. The order of the apparent capacity was K+ > Li+ ≈ Na+ ≈ Rb+ ≈ Cs+ at pH < 6. The Kd study showed the selectivity sequence of K+ > Rb+ > Na+ > Li+ for alkali–metal ions at the range of pH <5; H–BirMO sample showed markedly high selectivity for the adsorption of K+ ions. Preliminary investigations of the electrochemical properties of the Li+-inserted sample Li–BirMO(1M, 6d) showed that the obtained samples had a relatively high discharge capacity of 115 mAh g−1 and excellent layered stability.