Composition-Dependent Structural Evolution and Electrochemical Behavior in MoS2-WS2 Systems

Abstract We report a systematic study of hydrothermally synthesized Mo1−xWxS2 alloys (x = 0−1), correlating their structural, vibrational, morphological, and electrochemical properties with composition. The materials were prepared using ammonium tetrathiomolybdate and ammonium tetrathiotungstate precursors in an octylamine-mediated hydrothermal process at 200 °C. X-ray diffraction revealed that all samples exhibited expanded interlayer spacing, with low-angle reflections (∼9°−17°) indicative of non-ideal stacking associated with ammonium/amine intercalation rather than conventional 2H ordering. Raman spectroscopy confirmed the presence of the A1g and E2g1 vibrational modes, which shifted and broadened with the composition. The Mo-rich and W-rich samples displayed characteristic MoS2- and WS2-like signatures, respectively, whereas the intermediate compositions exhibited multiple vibrational components and peak broadening, reflecting compositional disorder and mixed bonding environments. Electron microscopy revealed a composition-dependent morphological evolution from well-defined nanosheets to disordered, partially exfoliated structures at intermediate compositions. These structural changes influenced the electrochemical behavior probed by cyclic voltammetry and electrochemical impedance spectroscopy Mo70W30 showed the lowest charge-transfer resistance (Rct ≈26.71 Ω), indicating favorable charge-transfer kinetics associated with moderate structural disorder and Mo−W electronic interactions. Here, MoxWy denotes the nominal Mo/W molar ratio of the precursors. In contrast, Mo30W70 exhibited the highest double-layer capacitance (Cdl ≈21.64 μF), consistent with its increased surface accessibility and higher defect density. The results demonstrate that the electrochemical performance is governed by the balance between structural disorder, interlayer accessibility, and electronic transport. These results establish a structure−composition−property relationship in Mo1−xWxS2 alloys and demonstrate that the intermediate compositions largely determine the functional response.