Ångstrom Resolved Real-Time Monitoring of Oxide Growth and Reduction on Noble and Engineering Metals

Structure and dynamics at electrochemical metal/liquid interfaces determine lifetime and stability of advanced and structural materials, and are fundamental to corrosive processes. Here, we present recent experiments with the newly developed and unique electrochemical surface force apparatus^1,2, which allow us to unravel electrochemical oxidation and reduction processes in real-time at well-defined and nano-confined electrodes. In particular, we monitor metal-oxide thin film formation with Å-accuracy during potentiostatic and potentiodynamic polarizations. In confined spaces we find unexpectedly strong electrochemical depletion forces acting between apposing surfaces during active electrochemical processes. Depending on the conditions, these forces are repulsive and can strongly overpower attractive Van der Waals forces, and the associated electric-field gradients might have significant effects in corrosive processes occurring in nano-confined spaces (such as crevices or pits). In addition, using the EC-SFA we have, for the first time, monitored oxide growth and reduction on noble metals (Au, Pt, Pd and Ir) in sulfuric acid solutions, as well as Nickel and Aluminum corrosion in confinement situations, with Ångstrom resolution in thickness and in real time with milliseconds resolution. Our experiments reveal stark differences of oxide thickness and its electronic properties during potentio-dynamic and potentio-static oxide growth, which will be discussed in the presentation.

1. Valtiner, M. et al. The Electrochemical Surface Forces Apparatus: The Effect of Surface Roughness, Electrostatic Surface Potentials, and Anodic Oxide Growth on Interaction Forces, and Friction between Dissimilar Surfaces in Aqueous Solutions. Langmuir 2012, 28(36), 13080-13093.

2. Israelachvili, J. N. et al The Intersection of Interfacial Forces and Electrochemical Reactions. J. Phys. Chem B, 2013, 117 (51), 16369–16387.