Scanning Electrochemical Microscopy of Single-Crystal Platinum Electrode

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.