Accurate vertical ionization energy and work function determinations of liquid water and aqueous solutions

  • The absolute-scale electronic energetics of liquid water and aqueous solutions, both in the bulk and at associated interfaces, are the central determiners of water-based chemistry. However, such information is generally experimentally inaccessible. Here we demonstrate that a refined implementation of the liquid microjet photoelectron spectroscopy (PES) technique can be adopted to address this. Implementing concepts from condensed matter physics, we establish novel all-liquid-phase vacuum and equilibrated solution–metal-electrode Fermi level referencing procedures. This enables the precise and accurate determination of previously elusive water solvent and solute vertical ionization energies, VIEs. Notably, this includes quantification of solute-induced perturbations of water's electronic energetics and VIE definition on an absolute and universal chemical potential scale. Defining and applying these procedures over a broad range of ionization energies, we accurately and respectively determine the VIE and oxidative stability of liquid water as 11.33 ± 0.03 eV and 6.60 ± 0.08 eV with respect to its liquid-vacuum-interface potential and Fermi level. Combining our referencing schemes, we accurately determine the work function of liquid water as 4.73 ± 0.09 eV. Further, applying our novel approach to a pair of exemplary aqueous solutions, we extract absolute VIEs of aqueous iodide anions, reaffirm the robustness of liquid water's electronic structure to high bulk salt concentrations (2 M sodium iodide), and quantify reference-level dependent reductions of water's VIE and a 0.48 ± 0.13 eV contraction of the solution's work function upon partial hydration of a known surfactant (25 mM tetrabutylammonium iodide). Our combined experimental accomplishments mark a major advance in our ability to quantify electronic–structure interactions and chemical reactivity in liquid water, which now explicitly extends to the measurement of absolute-scale bulk and interfacial solution energetics, including those of relevance to aqueous electrochemical processes.

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Author:Stephan ThürmerORCiD, Sebastian MalerzORCiD, Florian TrinterORCiDGND, Uwe HergenhahnORCiDGND, Chin LeeORCiD, Daniel M. NeumarkORCiD, Gerard MeijerORCiD, Bernd WinterORCiD, Iain WilkinsonORCiD
Parent Title (English):Chemical science
Place of publication:Cambridge
Document Type:Article
Date of Publication (online):2021/07/02
Date of first Publication:2021/07/02
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2022/08/04
Page Number:25
First Page:10558
Last Page:10582
The data of relevance to this study have been deposited at the following DOI: 10.5281/zenodo.5036382.
S. T. acknowledges support from the JSPS KAKENHI Grant No. JP18K14178 and JP20K15229. S. M., U. H., and B. W. acknowledge support by the Deutsche Forschungsgemeinschaft (Wi 1327/5-1). F. T., G. M., and B. W. acknowledge support by the MaxWater initiative of the Max-Planck-Gesellschaft. B. W. acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and investigation programme (grant agreement No. 883759). D. M. N. and C. L. were supported by the Director, Office of Basic Energy Science, Chemical Sciences Division of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 and by the Alexander von Humboldt Foundation.
All publication charges for this article have been paid for by the Royal Society of Chemistry
Institutes:Physik / Physik
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 53 Physik / 530 Physik
5 Naturwissenschaften und Mathematik / 54 Chemie / 540 Chemie und zugeordnete Wissenschaften
Licence (German):License LogoCreative Commons - Namensnennung 3.0