Ruthenium-Doping-Induced Amorphization of VS 4 Nanostructures with a Rich Sulfur Vacancy for Enhanced Hydrogen Evolution Reaction in a Neutral Electrolyte Medium.

The generation of pure H 2 from a neutral electrolyte solution represents a transformative route with low cost and environmentally friendly nature. However, the complex kinetics of hydrogen evolution reaction (HER) via water electrolysis make its practical application to be difficult. Herein, we have reported Ru-doping-induced formation of VS 4 nanostructures with a rich S vacancy for neutral HER in a 0.2 M phosphate buffer solution. The Ru-doped VS 4 demands an overpotential value of 160 mV at 10 mA/cm 2 current density with a lower catalyst loading of 0.1 mg/cm 2 , while pristine VS 4 demands a 374 mV overpotential with the same mass loading. 60 hours of chronoamperometric study reveals the excellent stability of Ru-doped VS 4 materials, which is the highest amount of time ever reported for neutral HER. The marginal degradation of a catalyst under a long-term stability study was confirmed through inductively coupled plasma mass spectrometry (ICP-MS) analysis. The introduction of Ru to the VS 4 lattice leads to a 4.35-fold increase in the turnover-frequency values compared to those of bare VS 4 nanostructures. The higher HER activity of S-vacancy-enriched VS 4 materials is thought to originate through effective water adsorption in S vacancy and Ru 3+ sites followed by the dissociation of a H 2 O molecule, and S 2 2- efficiently converts H ad to H 2 . Also, post-HER characterization reveals that the transformation of some Ru 3+ to Ru 0 additionally favored the HER by providing a better H adsorption site under a static cathodic potential.