In Situ Decoration of Ultrafine Ru Nanocrystals on N-Doped Graphene Tube and Their Applications as Oxygen Reduction and Hydrogen Evolution Catalyst

Development of significantly active and stable bifunctional catalysts toward hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) remains a challenge. It is also challenging to find a suitable support for the catalysts. Though the N-doped graphene tube (NGT) has many advantages over others due to its excellent electrical conductivity, high surface area, easy synthesis, and low cost, it shows very poor HER and ORR activity. Here, we report the in situ decoration of Ru nanocrystals (Ru NCs) on NGT (Ru@NGT) and their applications as efficient bifunctional electrocatalyst toward ORR and HER. The coordinated Ru complex (ruthenium acetylacetonate) is a unique precursor which directly converted to ultrafine (similar to 2 nm) and highly dispersed Ru NCs on NGT surface at low temperature without any treatment of the NGT surface. Because of strong coupling with the Ru on NGT, the hydrogen evolution activity drastically enhances. It shows zero onset potential and better current density as compared to 20% Pt/C catalyst in alkaline medium with long-term stability. The overpotential required to achieve a current density of 10 mA/cm(2) is 75 mV for Pt/C, whereas it requires only 45 mV for the three-dimensional electrode of Ru@NGT/Ni foam. Similarly, the Ru@NGT also shows excellent ORR performance with a limiting current density of 5.0 mA/cm(2) with long-term stability and alcohol tolerance activity. This high activity and better performance is due to the electron transfer from Ru NCs to NGT and better electron transfer within the NGT.