Templated electrochemical deposition of nanostructured macroporous PbO2

Abstract

We report a simple method for the preparation of novel nanostructured macroporous α- and β-PbO2 films with arrays of spherical pores arranged in a highly ordered close-packed structure. The nanostructured macroporous α- and β-PbO2 films were prepared by electrochemical deposition through the interstitial spaces between polystyrene spheres (500 or 750 nm in diameter) assembled on gold or indium tin oxide substrates. After deposition, the template was removed by dissolving in toluene to leave PbO2 films that have the inverse structure of the original template. Scanning electron microscopy and X-ray characterisation of the films shows a well-formed regular three-dimensional, porous α- or β-PbO2 framework, with the spherical pores arranged in a highly ordered close-packed three-dimensional structure. The spherical pores have the same diameter as the latex spheres used to form the templates and are interconnected through a series of smaller pores. The oxide frameworks are highly polycrystalline, self-supporting and free from defects. The confinement of α-PbO2 and β-PbO2 in the interstitial spaces between the polystyrene spheres that make up the template does not affect the mechanism of nucleation and deposition or the crystal structure of the oxide, as confirmed by scanning electron microscopy and X-ray characterisation. The electrochemical activity of the resulting macroporous β-PbO2 is greater than that of the corresponding plain film, as determined by the charge passed to convert the β-PbO2 to PbSO4 on electrochemical cycling in H2SO4. Due to the increase in volume accompanying the electrochemical conversion of β-PbO2 to PbSO4, the macroporosity of the film is significantly degraded and the electrochemical activity decreased after a few cycles in sulfuric acid.