Ångstrom Resolved Monitoring of Noble Metal Oxide Growth in Nano-Confined Spaces

Abstract

Structure and dynamics at electrochemical solid/liquid interfaces of metal electrodes drive functionality, stability and capabilities in a wide range of important technologies such as batteries, super capacitors, or fuel cells. In particular, with the downsizing of the electrochemical devices, electrochemistry in confined spaces (nanospaces) has become a major focus of current research efforts. We use a newly developed and unique electrochemical surface force apparatus1 in order to unravel electrochemical processes undergoing at well-defined nano-confined electrodes. We can monitor metal-oxide film formation with Å-accuracy during potentiostatic and potentiodynamic polarizations, within nano-confined spaces (less than 10 nm up to 100’s of nm). We report unexpectedly strong electrochemical depletion forces acting between apposing surfaces during active electrochemical processes such as potential pulse application or reduction of oxide. Such forces and the associated electric-field gradients might have significant effect in coarsening or mechanical dissolution of nano-confined spaces and confined particles. In addition, we are also able to reveal a real time in-situ monitoring of electrochemical interfaces with Angstrom resolution. We have, for the first time, monitored oxide growth on noble metals in sulfuric acid solutions in real time, with Ångstrom resolution in thickness and milliseconds resolution in time. Our experiments reveal stark differences of oxide thickness and electronic properties during potentio-dynamic and potentio-static oxide growth on noble metals, which will be discussed in the presentation.1. Valtiner, M.; Banquy, X.; Kristiansen, K.; Greene, G. W.; Israelachvili, J. N., 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.