Hydrothermal synthesis of spherical Ru with high efficiency hydrogen evolution activity

Hydrogen is an important renewable energy source. Electrochemical decomposition of water for hydrogen production has attracted more and more attention as an appealing hydrogen production strategy. Previous studies have proved that controlling the morphology of Ru can improve hydrogen evolution reaction (HER) activity. Therefore, the preparation of ordered spherical ruthenium nanocatalysts by hydrothermal method (Ru-HT) is described in this paper. The morphology, crystal structure and electronic state of Ru-HT were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). At the same time, the electrochemical properties and surface charge were studied and analyzed by cyclic voltammetry (CV) characterization and electrochemical impedance spectroscopy (EIS). The experimental results have demonstrated that the HER activity of Ru-HT is obviously better than that of Ru by liquid phase reduction method (Ru-LR). When HER current density reaches 10 mA cm−2, the overpotential of Ru-LR electrocatalyst is 88.8 mV, while the overpotential of Ru-HT electrocatalyst is reduced to 55.7 mV in acidic medium. The Tafel slope of Ru-HT is only 36.5 mV dec−1 and the exchange current density is 0.44 mA cm−2, which indicates the rate determining step of the HER process should be the electrochemical desorption step (Heyrovsky step). By adjusting hydrothermal time and hydrothermal temperature, HER activity was further optimized. During the optimization process, the preparation conditions would change the hydrogen adsorption intensity on Ru surface to some extent. The adsorption strength of RuH, together with the electrochemical surface area, will affect the HER activity of Ru.