Enhanced electrocatalytic activity of copper-cobalt nanostructures

Novel core-shell nanostructures containing Cu and Co have been synthesized using the microemulsion method at 700 °C. The core consists of Cu-Co composite particles, whereas the shell is composed of Cu-Co alloy particles (shell thickness ∼12 nm). It is to be noted that in bulk Cu-Co binary system there is practically no miscibility. TEM studies show formation of spherical-shaped nanoparticles of core-shell structures. The composition of the core (Cu-Co composite) and shell (Cu-Co alloy) were confirmed by XPS studies. The formation of the Cu-Co alloy as the shell is mainly driven by surface energy considerations. We have also obtained Cu-Co nanocomposites (by controlling the concentration of reducing agent) with particle size in the range of 40-200 nm. These Cu-Co nanostructures show ferromagnetic behavior at 4 K. The saturation magnetization of the core-shell (Cu-Co composite @ Cu-Co alloy) nanostructure (125 emu/g) is found to be higher than that of pure Cu-Co nanocomposite or alloy, which may be useful for applications as a soft magnet. Electrochemical studies of these nanocrystalline Cu-Co particles show higher hydrogen evolution efficiencies (∼5 times) compared to bulk (micrometer-sized) Cu-Co alloy particles.