Template conversion of MoO3 to MoS2 nanoribbons: synthesis and electrochemical properties

Abstract

Hydrothermally synthesized α-MoO₃ nanoribbons were converted to MoS₂ whilst retaining the same morphology by a solid–gas reaction at 800 °C in a H₂S/H₂/N₂ atmosphere. In order to keep the nanoribbon morphology from the oxide in the sulfide, it was crucial to have a H₂S stream during the whole heating process. Thereby, the first layer of sulfide is formed as soon as the oxide is activated avoiding coalescence of the nanoribbons. Afterwards, the sulfidization takes place from the outer shell to the inner core of the nanoparticles. Both α-MoO₃ and MoS₂-NR were investigated for the electrochemical intercalation of lithium-ions. The electrochemical insertion and removal of lithium in the molybdenum oxide are accompanied by a change of color, which was measured by in situ UV-Vis. Spectroelectrochemical experiments showed a distinguished electrochromic behavior with a significant potential-dependent change in absorbance at 660 nm upon Li⁺ insertion. Analysis of in situ voltammetry revealed the presence of three active sites for lithium insertion in the MoO₃-NRs, which are accompanied by only two chromophores in the same potential range. Voltammetric measurements of the MoS₂ nanoribbons presented a reversible reduction of MoS₂ to Li_xMoS₂, followed by Mo and Li₂S, which can be further reduced to Li and S at more negative potentials. Such sulfide materials are highly promising for lithium batteries. This template synthesis is a simple method to obtain high purity MoS₂ nanoparticles with a controlled morphology of nanoribbons.