Hollow Ag/MnO₂ Nanostructures with Controllable Shells: Synthesis and Oxygen Reduction Reaction Catalytic Performance

Novel hollow Ag/MnO₂ nanostructures with controlled shell composition and structure were designed and synthesized. In the present synthetic procedure, silver nanocrystals were oxidized by KMnO₄ , and MnO₂ was heterogeneously formed on the surface of silver nanocrystals, then released Ag⁺ was photoreduced to silver adjacent to MnO₂ . By simply changing the photoreduction moment, simultaneously with or after the addition of KMnO₄ , hollow Ag/MnO₂ structures with different shell architectures-a monolayered shell composed of evenly mixed silver and MnO₂ and a double-layered shell composed of an inner MnO₂ layer and an outer silver layer-can be obtained. Furthermore, the morphology of the hollow structure can be tuned by selecting different silver precursors, and the ratio of silver to MnO₂ in the shell can also be controlled by adjusting the ratio in the original reaction mixture. Electrochemical measurements revealed significantly enhanced catalytic performance in the oxygen reduction reaction for the prepared hollow structures. Compared with the Ag/MnO₂ composite, the onset potentials positively shift by about 50.0 mV and limiting current densities are nearly 2.0 times higher.