Gold-catalyzed formation of core-shell gold-palladium nanoparticles with palladium shells up to three atomic layers

Ultrathin metal layers formed on seed particles with different lattice parameters usually exhibit enhanced catalytic performance for a given chemical reaction due to the sufficient lattice strain effect induced by the core region. Herein, we report a gold-catalyzed strategy for the synthesis of core-shell gold-palladium nanoparticles with subnanometer-thick palladium shells towards oxygen reduction reaction. In this approach, owing to the catalysis of gold particles, the reduction of palladium precursors would only occur on the surface of gold cores, preventing the newly formed palladium atoms from self-nucleation. The deposition of palladium atoms gradually changes the surface property of gold seeds, and in particular, the catalytic reduction of palladium ions ceases when 3 palladium atomic layers are deposited on the gold cores. In comparison with the commercial palladium catalysts, the core-shell gold-palladium nanoparticles with subnanometer-thick palladium shells display superior activity and durability in catalyzing the oxygen reduction reaction, mainly due to the lattice tensile effect in palladium shells induced by the gold cores, which sufficiently balances the bond-breaking and bond-making steps of the oxygen reduction reaction process.