The kinetics of hydrogen evolution and oxygen reduction on Alloy 22 Alexei Davydov a , Konstantin V. Rybalka a , Louiza A. Beketaeva a , George R. Engelhardt b , Palitha Jayaweera c , Digby D. Macdonald d, * a Frumkin Institute of Electrochemistry, Russian Academy of Sciences, Moscow, Russia b OLI Systems, 108 American Road, Morris Plains, NJ 07950, USA c SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025, USA d Center for Electrochemical Science and Technology, Pennsylvania State University, State College, PA 16802, USA Received 12 January 2004; accepted 10 May 2004 Available online 15 July 2004 Abstract The kinetics of hydrogen evolution and oxygen reduction on Alloy 22 in 5 M NaCl+ xHCl+ yNaOH solutions as a function of pH at temperatures ranging from 20 to 95 °C have been investigated. The hydrogen evolution reaction proceeds via two basic mecha- nisms;thereductionofH þ atpH<4andthereductionofH 2 OathigherpHvalues.Analytical expressions for the exchange current density for the hydrogen evolution reaction on Alloy 22 are also developed for the two mechanisms, in a form that they can be used in corrosion models for assessing the performance of this alloy in high level nuclear waste (HLNW) repositories. The kinetics of oxygen reduction have also been explored over wide ranges of pH and temperature. However, this reaction is complicated by the formation of H 2 O 2 as an intermediate in a two-electron transfer reaction. Nevertheless, kinetic parameters have been obtained for this reaction and an expression has been developed that allows calculation of the exchange current density over a wide range of conditions. Finally, the kinetic data are used to identify probable mechanisms for hydrogen evolution and the reduction of oxygen on Alloy 22. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Hydrogen evolution; Oxygen reduction; Alloy 22 * Corresponding author. Tel.: +1-814-863-7772; fax: +1-814-863-4718. E-mail address: ddm2@psu.edu (D.D. Macdonald). 0010-938X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2004.05.005 www.elsevier.com/locate/corsci Corrosion Science 47 (2005) 195–215