Platinum and Palladium Overlayers Dramatically Enhance the Activity of Ruthenium Nanotubes for Alkaline Hydrogen Oxidation

Templated vapor synthesis and thermal annealing were used to synthesize unsupported metallic Ru nanotubes with Pt or Pd overlayers. By controlling the elemental composition and thickness of these overlayers, we obtain nanostructures with very high alkaline hydrogen oxidation activity. Nanotubes with a nominal atomic composition of Ru_0.90Pt_0.10 display a surface-specific activity (2.4 mA/cm²) that is 35 times greater than that of pure Ru nanotubes at a 50 mV overpotential and ∼2.5 times greater than that of pure Pt nanotubes (0.98 mA/cm²). The surface-segregated structure also confers dramatically increased Pt utilization efficiency. We find a platinum-mass-specific activity of 1240 A/g_Pt for the optimized nanotube versus 280 A/g_Pt for carbon-supported Pt nanoparticles and 109 A/g_Pt for monometallic Pt nanotubes. We attribute the enhancement of both area- and platinum-mass-specific activity to the atomic-scale homeomorphism of the nanotube form factor with adlayer-modified polycrystals. In this case, subsurface ligand and bifunctional effects previously observed on segregated, adlayer-modified polycrystals are translated to nanoscale catalysts.