Embodiments of the invention generally provide core-sheath nanostructures and methods for forming such nanostructures. In one embodiment, a method for forming core-sheath nanostructures includes stirring an aqueous dispersion containing silver nanostructures while adding a catalytic metal salt solution to the aqueous dispersion and forming catalytic metal coated silver nanostructures during a galvanic replacement process. The method further includes stirring an organic solvent dispersion containing the catalytic metal coated silver nanostructures dispersed in an organic solvent while adding a nickel salt solution to the organic solvent dispersion, and thereafter, adding a reducing solution to the organic solvent dispersion to form silver-nickel core-sheath nanostructures during a nickel coating process. In one embodiment, the core-sheath nanostructures are silver-nickel core-sheath nanowires, wherein each silver-nickel core-sheath nanowire has a sheath layer of nickel disposed over and encompassing a catalytic metal layer of palladium disposed on a nanowire core of silver.