Effect of Ball-Milling on the Physical and Electrochemical Properties of PbO2 and PbO2/BaSO4 Nanocomposite

High energy ball-milling (HEBM) of pure PbO2 and of mixtures of PbO2 with BaSO4 was performed as a function of time. The powders were characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy, while the intrinsic electrochemical properties of the powders were assessed in 1M H2SO4 using a cavity microelectrode (CME). During milling, there is a transition from a tetragonal structure (beta-PbO2) to an orthorhombic structure (alpha-PbO2) and, after 1 h, the powder is composed of similar to 80 wt% alpha-PbO2. The addition of BaSO4 doesn't influence the kinetics of the beta- to alpha-PbO2 transition. Also, during milling, the crystallite size of beta-PbO2 decreases from 25 to 8 nm, while the crystallite size of alpha-PbO2 is constant at 14 nm. During the first few hours of milling, there is a 50 mV shift of the potential corresponding to the maximum reduction and oxidation peak current towards less negative and positive values, respectively. This effect is emphasized by the addition of BaSO4, indicating that the reversibility of the PbSO4/PbO2 system is increased. This is thought to arise as a consequence of a reduction of the crystallite size and the presence of BaSO4. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.067201jes]