Transforming Mo0.5W0.5O3 to MoS2: leveraging selective sulfurization for enhanced electrocatalysis

Abstract

Conversion chemistry is a pivotal technique for transforming pre-synthesized nanocrystals into new materials with precise control over their properties. Herein, we have developed a selective sulfurization approach to convert transition mixed metal oxides to their sulfide counterparts. Mixed metal oxide W_0.5Mo_0.5O₃ with a nanobelt morphology has been synthesized as either hydrated (orthorhombic) phase or a non-hydrated (monoclinic) phase. Utilizing a simple hydrothermal method, we selectively sulfurized these phases using thiourea as a sulfur precursor, resulting in the formation of 2D MoS₂ with varying size of nanoflowers. The non-hydrated phase exhibited sulfurization kinetics faster than the hydrated phase, indicating that the presence of the water of hydration hindered the attack of incoming sulfide ions. Time-dependent ex situ experiments revealed the formation of MoS₂ layers originating from the oxide surface, leading to the formation of a WO₃–MoS₂ heterostructure as an intermediate. Furthermore, our synthesized WO₃–MoS₂ heterostructure exhibited superior performance than the template and final products for hydrogen evolution, oxygen evolution and water-splitting reactions, characterized by low overpotential, faster kinetics, high ECSA and increased BET surface area. Overall, this study establishes a pathway for the selective synthesis of 2D layered materials and their heterostructures from mixed metal oxides to design a bifunctional electrocatalyst for water-splitting reaction and can be extended to other materials.