Methodologies for Operando ATR-IR Spectroscopy of Magnesium Battery Electrolytes

Abstract

We explore the suitability of operando attenuated total reflection infrared (ATR-IR) spectroscopy methodologies for the study of organoaluminate electrolytes for Mg battery applications. The “all-phenyl complex” in tetrahydrofuran (THF), with the molecular structure [Mg2Cl3·6THF]+[AlPh4]−, is used as an exemplar electrolyte to compare two different spectroelectrochemical cell configurations. In one case, a Pt gauze is used as a working electrode, while in the second case, a thin (∼10 nm) Pt film working electrode is deposited directly on the surface of the ATR crystal. Spectroscopic measurements indicate substantial differences in the ATR-IR response for the two configurations, reflecting the different spatial arrangements of the working electrode with respect to the ATR sampling volume. The relative merits and potential pitfalls associated with the two approaches are discussed.

Precise Fingerprint Determination of Vibrational Infrared Spectra in a Series of Co(II) Clathrochelates through Experimental and Theoretical Analyses

“…We aimed to apply high-level quantum-chemical methods to compare the experimental IR spectra of these cobalt­(II) clathrochelates with theoretical predictions, thus providing a complete description of their normal modes of vibration. The analysis of Operando vibrational spectroscopy would require precise knowledge of the normal modes of the selected complexes aiming to establish the fingerprint of probable reactive intermediates. − The findings of this work would be useful for any future research regarding the vibrational spectroelectrochemistry of these compounds in Operando conditions and also to establish a clear methodology to predict the geometry and the standard redox potentials of specific clathrochelate complexes. In summary, this work will set the experimental and theoretical bases for the future detailed description of Operando vibrational spectroscopy of cobalt clathrochelate electrocatalysts under HER conditions.…”

Differentiating between Ion Transport and Plating–Stripping Phenomena in Magnesium Battery Electrolytes Using Operando Raman Spectroscopy

“…Analytical science has a critical role to play in the development of new electrolytes, by supporting improved understanding of interfacial processes and elucidation of degradation and failure mechanisms. , In this regard, operando spectroscopy, particularly vibrational methods such as Fourier transform infrared (FTIR) and Raman spectroscopy, are very useful because they allow direct observation of chemical speciation in electrolytes during electrochemical cycling . Our groups have been active in this area and recently used attenuated total reflectance (ATR)-FTIR to re-examine one of the most widely used Mg electrolytes, the “all phenyl complex” (APC), which is a solution of dimagnesium trichloride tetraphenyl aluminate in tetrahydrofuran (THF) (active species [Mg 2 Cl 3 ] + [AlPh 4 ] − , Figure a). − We demonstrated that the ATR-FTIR spectroelectrochemical response is very sensitive to interfacial transport effects and reveals crucial changes in coordination environment of the electroactive dinuclear cation and solvent during plating and stripping. Despite the potential insights available from FTIR, spectra can be difficult to interpret in isolation due to the dominance and convolution of multiple solvent bands in different local clustering and coordination states .…”

“…This cell allows optical access to the Pt gauze working electrode from the top via a sapphire optical window. The cell is geometrically equivalent to the coin cell-like configuration that we adopted for our recent ATR-FTIR study, 13 thus facilitating direct comparison between operando techniques, while also allowing specific spatial variations to be resolved.…”

“…It is unclear whether this background effect arises purely through the ERS mechanism or includes some contribution from fluorescence. However, the reversibility of the background intensity profile combined with the known stability of the APC electrolyte under these conditions 13,14 suggests that fluorescence from electrolyte degradation or SEI formation is less likely than the ERS mechanism to be the primary origin of the background variations. Irrespective of the mechanism, our evidence suggests that the background intensity may offer a means to probe the Mg plating−stripping process at the electrode/electrolyte interface, but further investigation is required to understand the sensitivity of the background intensity to Mg coverage and surface morphology.…”