Rapid assessment of platinum disk ultramicroelectrodes' sealing quality by a cyclic voltammetry approach

Here, we investigated the sealing quality between a microwire disk and the surrounding glass sheath of platinum disk ultramicroelectrodes (UMEs) using outer-sphere (ferrocene methanol, FcMeOH, oxidation) and inner-sphere electrochemical reactions (hydrogen underpotential deposition (HUPD) and the hydrogen evolution reaction (HER)) by the cyclic voltammetry (CV) approach. The tilt aspect in the CV curves is ascribed to the leakage of the electrolyte solution between the microelectrode wire and the glass sheath, causing an iR drop which shows the resistive nature of CV. The resistive nature of CV was analyzed by performing the HER using both poorly and well-sealed disk UMEs. Scan rate dependent double-layer capacitance (Cdl) data confirm the leak between a glass-wire interface in the UMEs. Further, we showed a quantitative treatment for the sealing assessment using analytical expressions. Overall, we demonstrate a rapid check procedure of the sealing quality in fabricating Pt disk UMEs. The simple procedure presented in this work can be used to evaluate the sealing quality of other types of micro/nanoelectrodes during their fabrication.