Probing calcium solvation by XAS, MD and DFT calculations

Calcium L-edge TEY mode XAS spectra for CaCl2⋅2H2O (a) aqueous solutions and (b) methanol solutions. (c) Molecular dynamics simulations for the first solvation shell around Ca2+ in 0.5 M CaCl2⋅2H2O methanol solution. (d) Absolute density distribution of oxygen atom as a function of the distance from Ca2+.

Scientific Achievement

The solvation shell structures of Ca2+ in aqueous and organic solutions are probed by calcium L-edge soft X-ray absorption spectroscopy (XAS) and DFT/MD simulations.

Significance and Impact

The calcium L-edge soft XAS demonstrates its sensitivity to the surrounding chemical environment. The total electron yield (TEY) mode as a surface sensitive probe shows its implications for future battery studies, especially for probing electrolyte/electrode interface for electrochemical reactions under in-situ/operando conditions.

Research Details

  • For CaCl2⋅2H2O aqueous solution, the intensity of the peaks is inversely correlated with the Ca2+ concentration because of the tetrahedral hydrogen-bonded network while for that in methanol the intensity remains similar while the concentration varies because only the first solvation shell is significant due to the weaker polarity and steric hinderance of CH3OH molecules compared to those of H2O.
  • The use of the flow liquid cell allows electrochemical potentials to be applied, which shows implications in probing transient state species at the interface which can only be observed under in-situ/operando conditions.

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DOI: 10.1039/d0ra05905f

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