In-Situ Solid-State Electrochemistry of Well-Defined Electrode-Electrolyte Interfaces Using Ion Soft Landing
Authors: Prabhakaran Venkateshkumar , Johnson Grant , Laskin Julia 
Published: February 2020

Molecular-level understanding of electrochemical processes at electrode-electrolyte interfaces (EEI) is key to the development of high-performance electrochemical technologies such as batteries, supercapacitors, and fuel cells. Soft landing of mass-selected ions is ideally suited for controlled preparation of well-defined surfaces necessary for understanding processes at EEI. Specifically, ion soft landing enables deposition of uniform layers of redox-active species onto electrode surfaces with precise control over the charge state, composition, and kinetic energy.(1-3) Herein, we report the development and first demonstration of the capabilities of an in-situ solid-state three electrode electrochemical cell for studying the electrochemical activity of mass- and charge- selected ionic clusters deposited onto electrode surfaces using ion soft landing. In-situ electrochemical cells were fabricated using carefully designed nanoporous ionic liquid membranes with excellent mass transfer properties compared to liquid electrolyte.(4) The in-situ electrochemical cell enables (i) characterization of both intrinsic redox and reactive processes with control over the stoichiometry and distribution of analyte species at EEIs using soft landing onto nanostructured solid-state electrolyte and (ii) understanding of the effect of diffusion of ions of interest through pores on their electrochemical activity.

The in-situ electrochemical cell was fabricated by depositing a ~10 µm thick room temperature ionic liquid - polymer electrolyte membrane on a screen printed electrode. The cell showed a stable rectangular double layer capacitive behavior both in high vacuum (10-5 Torr) and reactive gaseous environments. We demonstrate the performance of the in-situ electrochemical cell for studying both the intrinsic redox activity and reactive electrochemistry of well-defined ions at EEI. Specifically, we examined the intrinsic redox activity of mixed-addenda Keggin PMoxW12-xO40
3- (x=0,1,2,3,6,9,12) polyoxometalates. Multi-electron redox activity of stable anionic Keggin POMs that enable transfer of up to 24 electrons while retaining the structure of the cluster makes them attractive systems for studies in catalysis and energy storage.(5, 6) In addition, we examined the oxygen reduction reactivity of bare Pt cluster ions ∼1 nm in diameter produced using magnetron sputtering combined with gas aggregation. Soft landing of bare metal clusters directly onto the cell eliminates the need to use stabilizing ligands or solvent and, therefore, provides a direct route for studying intrinsic electrocatalytic activity.

In summary, the in-situ electrochemical cell combined with mass-selected ion deposition is a powerful approach for studying processes both at model and technologically-relevant EEIs during operating conditions.

References

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