Neutron diffraction study on the mechanism of the topotactic reduction of 2HTaS 2 electrodes

Abstract

The dynamic investigation by neutron diffraction of the topotactic reduction of 2HTaS 2 electrodes in K + D 2 O electrolyte to the ionic layered hydrate K + 0.5(D 2O) 0.5[TaS 2] 0.5− is shown to proceed via third-stage K + x (D 2O) y [TaS 2] 3 x− , second-stage K + x (D 2O) y [TaS 2] 2 x− , and first-stage K + x (D 2O) y [TaS 2] x− intermediates. A comparative study by X-ray diffraction on the cathodic intercalation of 2HTaS 2 and 2HNbS 2 electrodes with hydrated main group and transition metal ions reveals analogous behavior; the formation of higher-stage intermediates is supposedly correlated with stable electronic layer states. Influence of kinetic factors is observed for larger guest cations such as transition metal complexes and organic ions. CdI 2-type host lattices with an octahedral environment of intralayer cations shown different reaction pathways, although the occurrence of intermediate states (at least in the nucleation phase) can be demonstrated. It is concluded that the presence of ordered intermediate states is a general phenomenon in topotactic electrode processes of layered dichalcogenides.