| AVS 61st International Symposium & Exhibition | |
| Surface Science | Monday Sessions |
| Session SS+EN-MoA |
| Session: | Metals, Alloys and Oxides: Structure, Reactivity & Catalysis |
| Presenter: | Markus Valtiner, Max Planck Institut fur Eisenforschung GmbH, Germany |
| Authors: | B.R. Shrestha, Max Planck Institut fur Eisenforschung GmbH, Germany T. Baimpos, Max Planck Institut fur Eisenforschung GmbH, Germany S. Raman, Max Planck Institut fur Eisenforschung GmbH, Germany M. Valtiner, Max Planck Institut fur Eisenforschung GmbH, Germany |
| Correspondent: | Click to Email |
Electrochemical metal-oxide|liquid interfaces are critically important for a variety of technological applications and materials for energy storage, harvesting and conversion. Yet, a real-time Ångstrom-resolved visualization of dynamic processes at electrified metal-oxide|liquid interfaces has not been feasible. Here we present a unique direct and real-time atomistic experimental view into dynamic processes at electrochemically active metal interfaces using white light interferometry in an electrochemical surface forces apparatus. This method allows to simultaneously decipher both sides of an electrochemical interface - the solution side and the metal side - in real-time under dynamically evolving reactive conditions, which are typically found in technological systems in operando. Quantitative in situ analysis of the electrochemical oxidation and reduction of noble metal surfaces shows that the Å-thick oxide films formed on Au and Pt are reflecting high-ik materials, i.e. they are metallic or highly doped semiconductors, while Pd forms a transparent low-ik oxide during dynamic change of applied electrochemical potentials. In contrast, under potentiostatic growth conditions all electrochemically grown noble metal oxides are transparent, with thicknesses ranging from 2-10 Å. On the solution side the data simultaneously reveals hitherto unknown strong electrochemical depletion forces, which are due to a temporary charge imbalance in the electric double layer caused by the consumption or generation of charged species. The real time capability of our approach shows significant time lags between electron transfer, oxide reduction/ oxidation and solution side equilibration during a progressing electrode process. Comparing the kinetics of solution side and metal side reactions provide detailed experimental evidence that noble metal oxide reduction initiates via hydrogen loading and subsequently proceeds via a dissolution/ re-deposition mechanism. The presented approach may have important implications for designing emerging materials utilizing electrified interfaces such as fuel cells, batteries or super-capacitors.