Bipolar Electrodeposition of Manganese Dioxide Nanoparticles on Gold Nanotubes

Manganese dioxide is an environmentally abundant and low-cost material that shows considerable interest for energy-related applications, such as supercapacitor and cathode material in batteries. However, its use is currently limited by its poor cyclability and its low ionic and electronic conductivities. To overcome these limitations, many strategies have been centered on the design of MnO2 nanoparticles to reduce the diffusion distance for the insertion cations. Precisely controlling the location of MnO2 nanoparticle electrodeposition on the electrode can be challenging because of the need of continuous electrical contact. This is why we have developed a method to grow MnO2 nanoparticles on 3D nano-objects in the absence of a direct electrical contact. This method entails using gold nanotubes as bipolar electrode. A voltage of 2 V is applied across a gold nanotube membrane to generate redox reactions, one cathodic and one anodic, at either end of the tubes. The anodic reaction is chosen such that it forms MnO2 hemispherical nanoparticles at one opening of the nanotubes. In this presentation, we will describe the mechanism of electrodeposition and growth rate of these MnO2 nanoparticles, as studied by electron microscopy, X-ray photoelectron spectroscopy and electrochemical techniques. We will also report chemical and electrochemical characterizations of these nanoparticles, such as conductivity and permselectivity measurements in lithium solution, in order to address the performance of MnO2 as a battery material. Finally, the effect of charging and discharging on the structure and electrochemical properties of MnO2 will be presented.