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Heterogeneous Chemistry at Aqueous Interfaces Investigated with Ambient Pressure X-ray Photoelectron Spectroscopy

Aqueous interfaces govern important phenomena in technology, catalysis, electrochemistry and the environment.[1,2]  These systems include solid-liquid, liquid-vapor and solid-vapor interfaces.  Among the questions of interest are the first stages of water adsorption at solid surfaces, which has a strong influence on, e.g., the formation of seeded cloud droplets. Liquid-vapor interfaces hold special interest for the uptake and release of trace gases by aqueous aerosols and CO₂ sequestration by the oceans. Solid-liquid interfaces are at the heart of electrochemical and corrosion phenomena. 

A detailed understanding of these processes requires the investigation of aqueous interfaces with chemical sensitivity and interface specificity under ambient conditions, i.e., temperatures above 200 K and water vapour pressures in the millibar to tens of millibar pressure range.  This talk will discuss opportunities and challenges for the investigations of aqueous interfaces using ambient pressure X-ray photoelectron spectroscopy.[3,4]  We will discuss the fundamental challenges to performing XPS experiments at elevated pressures and how to overcome them.  Examples of the application of ambient pressure XPS to the study of water adsorption on oxide surfaces, the observation of short-lived reaction intermediates in aqueous solution and the investigation of electrical field gradients at semiconductor-solution interfaces will be presented as well.

[1] O. Björneholm, M.H. Hansen, A. Hodgson, L.-M. Liu, D.T. Limmer, A. Michaelides, Ph. Pedevilla, J. Rossmeisl, H. Shen, G. Tocci, E. Tyrode, M.-M. Walz, J. Werner, H. Bluhm, Chem. Rev. (2016).

[2]  A. Verdaguer, G.M. Sacha, H. Bluhm, M. Salmeron, Chem. Rev. 106, 1478 (2006).

[3]  H. Siegbahn, J. Phys. Chem. 89, 897 (1985).

[4]  D.E. Starr, Z. Liu, M. Hävecker, A. Knop-Gericke, H. Bluhm, Chem. Soc. Rev. 42, 5833 (2013).