Scanning Electrochemical Microscopy of Single-Crystal Platinum Electrode

TL;DR

Researchers developed a new glass cell to study electrochemical reactions on single-crystal platinum surfaces using scanning electrochemical microscopy.

Contribution

A precision glass cell was designed to enable SECM of single-crystal Pt(111) surfaces, overcoming orientation limitations.

Findings

The new glass cell allows for clean and contamination-free SECM of Pt(111) surfaces.

SECM detected proton transfer dynamics during redox reactions on Pt(111) surfaces.

The butterfly peak in voltammetry was found to have a nonfaradaic origin.

Abstract

The surface of single-crystal
metal electrodes can be well controlled
at the atomic level to serve as superior models for fundamental electrochemistry
in comparison with the polycrystalline counterparts. The single-crystal
surface of a metal can be cleaned thermally and oriented downward
to form a meniscus contact with an electrolyte solution for diverse
electroanalytical characterization. Problematically, the widely used
hanging-meniscus configuration is incompatible with scanning electrochemical
microscopy (SECM), which requires the upward orientation of the single-crystal
surface to an ultramicroelectrode tip. Herein, we report a precision-made
glass cell to enable SECM of a disk Pt(111) substrate as a well-established
model of single-crystal metal electrodes. The clean glass cell can
accommodate the flame-annealed Pt(111) disk without adventitious contamination
and solution leakage. The cleanliness of the entire Pt(111) surface
is confirmed by cyclic voltammetry in perchloric acid and sulfuric
acid to observe characteristic surface waves with butterfly peaks.
We employ SECM to monitor the redox dynamics of underpotential hydrogen
deposition, hydroxyl adsorption, and hydrogen oxidation at the clean
Pt(111) surface under the tip. These electron-transfer reactions are
coupled with proton transfer to generate and consume H+, which is detected amperometrically at the tip while the substrate
potential is cycled. Interestingly, the tip current changes only slightly
while a sharp butterfly peak is observed at the substrate, thereby
indicating an unexpected nonfaradaic origin of the well-known peak.
The new glass cell will be useful for in situ SECM of electrocatalytic
reactions and intermediates at various single-crystal metal electrodes.

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