The electrodeposition of highly reflective lead dioxide coatings C.T.J. Low a, * , D. Pletcher b , F.C. Walsh a a Electrochemical Engineering Laboratory, Energy Technology Research Group, School of Engineering Sciences, University of Southampton, Highfield, Southampton SO17 1BJ, United Kingdom b Electrochemistry and Surface Science Group, School of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, United Kingdom article info Article history: Received 28 March 2009 Received in revised form 23 April 2009 Accepted 28 April 2009 Available online 6 May 2009 Keywords: Electrodeposition Reflective Lead dioxide Methanesulfonic acid abstract In the presence of a suitable surfactant, such as hexadecyltrimethylammonium chloride or bromide, highly reflective and hard lead dioxide coatings with a black appearance can be electrodeposited from methanesulfonic acid media at room temperature (295 K). The reflective PbO 2 coatings are compact, adherent to the (vitreous carbon or carbon-polymer) substrate and can be formed at current densities of 10 to 100 mA cm À2 at a thickness up to several hundred microns. The coatings were characterised by measurement of surface optical reflectance, surface roughness, surface microstructure, phase compo- sition and crystallite size. The reflective PbO 2 films were found to mainly consist of the alpha (orthorhom- bic) phase with feather-like and orientated microstructures. The crystallite size and surface roughness were in the order of tens of nanometres and their optical reflectance was several orders of magnitude higher than matte coatings produced in the absence of additives. Crown Copyright Ó 2009 Published by Elsevier B.V. All rights reserved. 1. Introduction Recent years have seen extensive studies of the anodic deposi- tion of lead dioxide onto inert substrates, as seen in [1–3] and ref- erences therein. Such coatings are relatively low in cost and can provide stable and robust structures for anodic oxidation at very positive potentials. Most recently, the focus of development has been to identify preparations of lead dioxide with improved char- acteristics e.g. higher catalytic activity and enhanced stability. In Southampton, interest has focused on deposition from methane- sulfonic acid media [4–10] because lead(II) is highly soluble and this acid is non-oxidising, relatively non-corrosive and biodegrad- able [11]. In this communication, we report the anodic deposition of lead dioxide deposits on carbon substrates with unusual charac- teristics. The deposits are black, hard and highly reflecting. 2. Experimental details The electrolytes contained 0.5–1.5 mol dm À3 lead(II) methane- sulfonate, 0.2–1.5 mol dm À3 methanesulfonic acid. The additives used were hexadecyltrimethylammonium chloride, bromide, hydroxide and 0.1–1 mmol dm À3 p-toluenesulfonate. All chemicals were analytical reagent grade from Sigma Aldrich UK. All electrochemical measurements were made with an EcoChe- mie Autolab (PGSTAT20) computer controlled potentiostat using the General Purpose, Electrochemical Software (GPES) Version 4.5. Cyclic voltammetry was performed at a static glassy carbon disc electrode (area, 0.126 cm 2 ) in a three-electrode, two-compart- ment glass cell. Constant current deposition was carried out in an undivided parallel plate, ‘beaker’ cell at current densities from 10 to 100 mA cm À2 . The deposition time ranged from 10 minutes to 2 h and the temperature of the electrolyte was controlled at 283–333 K. The electrolyte volume was approximately 70 cm 3 .A magnetic stirrer (PTFE-coated steel cylindrical stirrer bar, 4.5 cm length and 0.8 cm diameter), c.a. 300 rpm, was used to generate flow in the solution. The working electrode (1.0 cm width and 4.0 cm height) was a carbon-polymer composite (Type: BMC940) from Entegris GmbH, Germany and the sides and back were cov- ered with insulating material. Nickel plate (4 cm  1 cm) was the counter electrode. The interelectrode separation was 1.0 cm. Be- fore each experiment, all electrodes were mechanically roughened using 1200 and 4000 grade SiC paper then ultrasonically cleaned in detergent and distilled water. Surface roughness was measured using an atomic force micro- scope from Asylum Research MFP-3D TM AFM. Silicon tips were used and the measurements were carried out using AC mode imaging in the open atmosphere. X-ray diffraction patterns were measured using a Siemens D5000 diffractometer, 2h from 20 to 90° using Cu Ka, k = 0.154056 nm. Optical reflectance index was measured using an Avantes Avanspec-2048FT (Anglia Instruments Ltd.) de- vice at wavelengths 460–910 nm. Microstructural characterisa- tions were carried out using a scanning electron microscopy and energy dispersive X-ray spectroscopy (XL30ESEM, Philips), a 15 kV accelerating voltage and 5 minutes collection time. 1388-2481/$ - see front matter Crown Copyright Ó 2009 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2009.04.032 * Corresponding author. Tel.: +44 (0)23 8059 7052; fax: +44 (0)23 8059 7051. E-mail address: C.T.J.Low@soton.ac.uk (C.T.J. Low). Electrochemistry Communications 11 (2009) 1301–1304 Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom