Enhanced Electrocatalytic Hydrogen Evolution with Bimetallic Ru/Pt Nanoparticles Supported on Nitrogen-Doped Reduced Graphene Oxide

Abstract

The electrocatalytic hydrogen evolution reaction (HER) has been explored using mono- and bimetallic Pt-Ru nanoparticles (NPs) deposited onto nitrogen-doped reduced graphene oxide (NH2-rGO) in acidic media. In this contribution, monometallic and bimetallic nanoparticles with three different Pt/Ru ratios (1/5, 1/1, and 5/1) have been used, yielding five different materials denoted as PtxRuy@NH2-rGO (x = 0, y = 1; x = 1, y = 0; x = 1, y = 5; x = 1, y = 1; x = 5, y = 1). The materials were characterized using a variety of state-of-the-art techniques, including high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), energy dispersive X-Ray spectroscopy (EDX) and X-Ray absorption spectroscopy (XAS), enabling the investigation of differences in morphology, coordination environment and oxidation state as a function of the metal composition of the graphene-supported NPs. The materials exhibited HER activity and demonstrated competitive overpotentials close to the thermodynamic limit. The initial catalytic activity of the as-synthesized materials enhances as the Pt/Ru ratio increases. Chronopotentiometry cathodic experiments showed that under reductive conditions the electrocatalytic performance is drastically impacted. Ru-rich materials were activated, whereas Pt-rich materials showed poor stability. Upon applying a reducing potential for 58 h, Pt1Ru5@NH2-rGO reached the best catalytic activity with outstanding overpotentials of h0 = 0 mV and h10 = 3 mV and no signs of deactivation even after 12 additional hours of electrolysis. According to DFT calculations, all nanoparticles present surface sites whose hydrogen adsorption energy is optimal for HER. In agreement with the experimental data, the Pt1Ru5 model shows the highest number of highly active sites, especially those involving Ru centres close to the Pt-Ru interface. Combining thorough characterization and computational modelling, this work reveals that the synergy between the two metals, structural features, and their affinity for the support are responsible for the observed differences in catalytic activities and stabilities.