Ruthenium nanodendrites on reduced graphene oxide: an efficient water and 4-nitrophenol reduction catalyst

With synergy of structural stability and availability of plenty of active sites with open structure for better reactant/product accessibility, dendritic nanostructures stand alone. However, the complexities/difficulties in their design have largely hindered their wide-scale adoption in catalysis. Herein, with this work we report a green and new protocol for the synthesis of unsupported as well as reduced graphene oxide (rGO)-reinforced dendritic Ru nanostructures (Ru@rGO) via controlled galvanic replacement reaction with Mg as the sacrificial metal. Interestingly, experimental findings elucidate Ru@rGO as a promising electrocatalyst for hydrogen evolution reaction (HER) in a wide range of pH with nearly zero onset potential and superior current density as compared with the state-of-art Pt/C catalyst in alkaline as well as acidic media. It requires only 32 and 68 mV overpotential (eta) to achieve a current density of 10 mA cm(-2) in 1 M KOH and 1 M H2SO4 solution, respectively. Poisoning test conducted in the presence of thiocyanate (SCN-) elucidates the direct involvement of Ru nanostructures. Overall, the unique morphology and the interaction between Ru dendrites with rGO lead to the high HER activity. In addition to electrocatalytic superiority, Ru@rGO is found to be an effective catalyst for the reduction of 4-nitrophenol (an industrial waste) to 4-aminophenol (a value-added product) indicating its bi-functionality as well as adaptive nature for different catalytic environments. This green synthesis protocol driven by the respective redox energy level positioning of Mg, rGO and Ru, as revealed by ultraviolet photoelectron spectroscopic studies, opens up the potential to develop various mono-/bi-metallic nanodendrites for renewable energy harvesting and neutralizing the toxic chemicals in wastewater for environmental remediation.