| AVS 62nd International Symposium & Exhibition | |
| In-Situ Spectroscopy and Microscopy Focus Topic | Wednesday Sessions |
| Session IS+AS+SA+SS-WeM |
| Session: | In-situ Studies Using X-ray Absorption Spectroscopy and Vibrational Spectroscopy for Catalytic and Energy Materials |
| Presenter: | Chenghao Wu, University of California, Berkeley and Lawrence Berkeley National Laboratory |
| Authors: | C.H. Wu, University of California, Berkeley and Lawrence Berkeley National Laboratory J.-H. Guo, Lawrence Berkeley National Laboratory M.B. Salmeron, Lawrence Berkeley National Laboratory |
| Correspondent: | Click to Email |
Most of the electrochemistry processes occur within the thin layer of electrolyte at the electrolyte/electrode interfaces, commonly denoted as the electrical double layer (EDL). Although some classic continuum theories about EDL have been established and widely accepted over the past century, very little experimental information is available regarding the molecular-level details at such solid/liquid interfaces. We have developed in-situ liquid cells to study such solid/liquid interfaces by means of soft x-ray absorption spectroscopy [1]. Because the fluorescence x-ray photon has much larger mean free path in condensed matters than the secondary electrons, by comparing the total fluorescence yield (TFY) and total electron yield (TEY) spectra, we can extract useful information about the compositional, structural or chemical difference between the bulk and the interfacial electrolyte. Under different bias, by modulating the incident x-ray, the TEY signal current becomes alternating and can be separated from the dominant faradaic current so that we can obtain surface-sensitive TEY signal under electrochemical conditions.
With this in-situ and operando XAS technique, we investigated the gold/water interface [1] and platinum/sulfuric acid solution interface. It was found that at gold/water interface, the interfacial water layer has significantly different hydrogen-bonding network structure compared to the bulk water. Under different bias, the polar water molecules respond to the external electrical field and reorient at the gold electrode surface, which significantly changes the amount of distorted or broken hydrogen bonds. First-principle simulations were able to corroborate the experimental results and qualitatively reproduce the change in the x-ray absorption spectra at different bias. In the platinum/sulfuric acid system, the charged solute species, such as SO42- ions, hydronium ions, introduce extra complexity at the surface under different bias. Using the same in-situ technique, we were also able to identify some intermediate surface species in the potential window of OER reaction.
[1]. J.J. Velasco-Velez, C.H. Wu, T.A. Pascal, L.F. Wan, J.-H. Guo, D. Prendergast, and M. B. Salmeron, Science, 346, 831-834 (2014).