Manganese Dioxide Nanoparticle Synthesis on Gold Nanotubes

Emily P. Johnson, Juliette Experton, Charles R. Martin

Department of Chemistry, University of Florida, Gainesville, FL 32611

Manganese dioxide is a naturally abundant material that is of interest for a wide variety of applications including catalysis, electronics and sensing. In lithium-ion batteries, Mn(IV) can be reduced to Mn(III) by intercalating lithium ions to produce Li_xMnO₂. This intercalation mechanism is favored by the porous structure of MnO₂. However, Li diffusion can be slow if the MnO₂ is too bulky, reducing the capacity and power delivered by the battery. Therefore, there has been considerable interest in developing an efficient method for the synthesis of MnO₂ nanoparticles to decrease the diffusion distances for the transport of lithium ions in batteries.

We have previously developed a bipolar electrodeposition method where a voltage was applied across a gold-nanotube membrane to oxidize Mn²⁺ and form MnO₂ nanoparticles at one end of gold nanotubes. In this method, the membrane was placed between a solution of sodium sulfate and a solution of sodium sulfate and manganese(II) acetate. In an attempt to lower the voltage applied across the membrane, we replaced the solution of sodium sulfate by a solution of iron(III) chloride. Surprisingly, the formation of MnO₂ was then spontaneous and occurred without applying a voltage across the membrane. MnO₂ nanoparticles were not observed when the membrane did not contain gold nanotubes or when the two solutions of manganese acetate and iron chloride were mixed.

In this poster presentation, we will present the mechanism of the formation of MnO₂ nanoparticles with iron chloride. We will also show X-ray photoelectron spectroscopy, microscopy and electrochemical characterizations of these nanoparticles.