In Situ Infrared Spectroelectrochemistry for Understanding Structural Transformations of Precisely Defined Ions at...

Understanding the intrinsic properties of electroactive species at electrode-electrolyte interfaces (EEIs) is essential to the rational design of high-performance solid-state energy conversion and storage systems. In situ spectroscopy combined with cyclic voltammetry (CV) provides insights into structural changes of electroactive species at functioning EEIs. Ion soft landing enables precisely controlled deposition of mass- and charge-selected ions onto electrode surfaces thereby avoiding the contamination inherent with conventional electrode preparation techniques. In this contribution, we describe a new approach for the simultaneous electrochemical and spectroscopic characterization of soft-landed ions at operating solid-state EEIs. The technique exploits a specially fabricated three-electrode cell that is compatible with in situ infrared reflection absorption spectroscopy (IRRAS) characterization of the soft-landed ions. Keggin polyoxometalate (POM) anions, PW₁₂O₄₀^3-, were selected as a model system for these experiments due to their multielectron redox activity, structural stability, and well-characterized IRRAS spectrum. In situ CV measurements indicated continuous multielectron transfer processes of the soft-landed PW₁₂O₄₀^3- anions over a large potential range of -2.1 to -0.3 V. A distinct shift in the wavenumber of the terminal W═O_t stretching vibration in the IRRAS spectra was observed during the multielectron reduction process. The results demonstrate the capabilities of the in situ spectroelectrochemical approach for examining structural changes of well-defined electroactive species during electron-transfer processes at operating solid-state EEIs.