Facile Single-Step Synthesis of PVP-Stabilized Ru NPs for Electrochemical Hydrogen Generation

An efficient electrochemical hydrogen generation catalyst composed of robust ruthenium nanoparticles (Ru NPs) was synthesized through a simple one-pot hydrothermal reaction, where formaldehyde was employed as a reductant and low-molecular-weight poly(vinylpyrrolidone) (PVP) was employed as a stabilizing agent. The as-synthesized nanoparticles were initially characterized by powder X-ray diffraction, which confirmed their hexagonal, close-packed ruthenium phase. Structural analysis was performed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which disclosed PVP-stabilized nanoflowers composed of Ru NPs with an average diameter of 5 nm. Further, energy-dispersive X-ray spectroscopy (EDX) confirmed the presence of ruthenium and carbon, and their oxidation states were also studied with X-ray photoelectron spectroscopy (XPS). The as-synthesized PVP-supported Ru NPs exhibited remarkable hydrogen evolution reaction (HER) activity, with overpotentials of 51 and 39 mV at a cathodic current density of −10 mA cm–2 and corresponding Tafel slopes of 23 and 40 mV dec–1 in acidic and alkaline conditions, respectively. Such a high performance of the PVP-protected Ru NPs was further evaluated in a continuous manner by using an electrolyzer flow cell, and our findings were supported by the corresponding density functional theory (DFT) calculations. Calculations of the Gibbs free energy for varied surface coverage on the (002) facet revealed that the individual site activity improved with an increase in surface coverage, enhancing the continuous HER performance. Besides reinforcing the exploitation of eco-friendly raw materials for nanocatalyst development, this work serves as a prelude to our upcoming systematic investigations on the influence of the molecular weight of the PVP polymer on the size of metallic nanoparticles.