Electrosynthesis of Bifunctional WS₃-x/Reduced Graphene Oxide Hybrid for Hydrogen Evolution Reaction and Oxygen Reduction Reaction Electrocatalysis

A multitude of research into the application of transition-metal dichalcogenides as earth-abundant hydrogen evolution reaction (HER) electrocatalysts has been conducted. However, current synthetic methods generally deploy environmentally harmful chemicals and energy-consuming reaction conditions, despite the primary intent to attain renewable energy production. Here, the desirable properties of tungsten sulfide and reduced graphene oxide (rGO) have been combined and hybrid materials have been fabricated through simultaneous electrochemical reduction and synthesis, as a versatile and environmentally benign alternative to conventional fabrication techniques. Through concurrent studies of three rGO materials, the precursor of which was graphene oxide (GO), produced by Hummers, Staudenmaier, or Hofmann oxidation methods, the importance of the choice of oxidation method employed prior to the fabrication of the hybrid was shown. In this cardinal study, a mixed WS₂/WS₃ film-like material (WS₃-x) was synthesized directly onto GO-modified glassy carbon electrodes by cyclic voltammetry and the resultant hybrid materials (WS₃-x/rGO) were thoroughly characterized by SEM, energydispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The excellent bifunctional electrocatalytic performances of WS₃-x/rGO towards both HER and oxygen reduction reaction stemmed from the coupled impacts of amplified electrical conductivity and surface area of rGO; the presence of metallic species within rGO, resulting from the oxidation process; and the amount of WS₃-x successfully electrodeposited in the hybrid. The efficacious fabrication of the WS₃-x/rGO composite through electrosynthesis reveals an innovative and eco-friendly methodology for the development of cost-effective and highly active bifunctional electrocatalysts for renewable energy generation.