Ru-based nanoparticles supported on carbon nanotubes for electrocatalytic hydrogen evolution: structural and electronic effects

The performance of Ru-based nanoparticles (NPs) in the hydrogen evolution reaction (HER) relies on both their structural properties and the oxidation state of the metal. Herein, the versatility of the organometallic approach for the synthesis of metal-based nanostructures is combined with thermal oxidation treatments to prepare carbon-nanotube (CNT)-supported Ru-containing nanomaterials for their use as electrocatalysts after dropcasting onto a glassy carbon rotating disk electrode. This strategy allowed access to a series of hybrid nanomaterials of different Ru/RuO2 compositions and different structural order. Linear sweep voltammetry experiments show that the relative disposition of the Ru/RuO2 phases, their interconversion under reductive turnover conditions and the degree of structural order affect the HER electrocatalytic performance of different materials. The electrode containing NPs consisting of a RuO2 core and metallic Ru at the surface outperforms that containing either pure RuO2 NPs or Ru NPs. Impedance spectroscopy studies and DFT calculations suggest that this catalytic activity enhancement arises from improved charge transport properties and from the structure of the exposed metallic Ru shell, which is partially oxidized and highly amorphous.