Microwave-Initiated Synthesis of Metal Chalcogenides/Graphene-Catalyst for Enhanced Hydrogen Evolution Reaction

In present days, new types of renewable energy resources are being developed to resolve the world energy crisis. Nanomaterials, such as carbon nanotubes, metal oxides, metal chalcogenides (MCs) and conducting polymers with superior mechanical, thermal and electrical properties, lead to broad applications in composite materials, smart structures, chemical sensors, energy storage and nano-electronic devices. However, the high cost and difficulty in producing large scale, high quality nanomaterials remain challenges. The present work successfully demonstrates the production of MCs on graphene substrate through ultra-fast (60 seconds), facile and energy-efficient microwave-initiated approach. Graphene plays a vital role during the synthesis process by absorbing microwave energy and converting it to heat energy, which facilitates the precursors to react vigorously. Moreover, high specific surface area and conductivity of graphene delivers a favorable conductive network for the uniform growth of MCs, along with rapid charge transfer kinetics. The electrochemical characterizations reveal that the as-produced nanocomposites can be used for hydrogen evolution reaction (HER) to generate useful hydrogen fuel. As an example, the molybdenum disulfide on graphene (MoS2/graphene) composite exhibits superior electrocatalytic activity for the HER in acidic medium, with a low onset potential of only 100 mV and a Tafel slope of 43.3 mV per decade, suggesting the Volmer-Heyrovsky mechanism of hydrogen evolution. Beyond excellent catalytic activity, MoS2/graphene reveals an unusual ability to enhance the accessible active sites during the HER proceeds. This leads to a long cycling stability with a very high cathodic current density, providing the opportunity of practical application for scalable processing. Therefore, this single-step microwave approach can be universally employed to produce other useful MCs (e.g., MoSe2, WS2, WSe2 etc.), that will catalyze substantial development in more widespread uses of MC-based nanocomposites for successful energy applications.