Enabling Alkaline Scanning Electrochemical Cell Microscopy (SECCM) for the Study of Water-Splitting Electrocatalysts

Spatially resolved electrochemical techniques are critical for advancing nanoscale structure–function studies of electrocatalytic materials, enabling direct correlation between the surface structure and activity of, for example, advanced water-splitting electrocatalysts. Among these techniques, scanning electrochemical cell microscopy (SECCM) offers unique capabilities for spatially resolved structure–electrochemical activity mapping but faces significant challenges in alkaline media due to unstable droplet cell contact and resulting excessive surface wetting during prolonged scanning. In this work, eight electrolyte additives─glycerol, carboxymethyl cellulose, guar gum, polyvinylpyrrolidone (PVP), propylene carbonate, 1-butyl-3-methylimidazolium tetrafluoroborate, polyethylene glycol (PEG), and polyethylene glycol dimethyl ether─are evaluated to identify suitable candidates for droplet cell stabilization in alkaline SECCM. Selection criteria include (1) chemical and electrochemical inertness; (2) lack of specific interaction with (or specific adsorption on) electrode (electrocatalyst) surfaces; and (3) physical stabilization of the droplet cell at low concentrations of additives. Among the additives tested, PEG (0.2–1 wt %) is the most effective, providing stable SECCM operation in 0.1 M KOH without significantly perturbing the intrinsic activity (i.e., in the absence of an additive) of polycrystalline Pt (poly-Pt) and Au electrodes. In contrast, PVP, though recently reported as effective, is shown to interfere with the surface activity of poly-Pt in 0.1 M KOH, consistent with its known surface affinity for (noble) metals. These results establish PEG as a reliable additive for alkaline SECCM and offer practical guidelines for additive selection, ultimately enabling high-resolution electrochemical imaging of electrocatalyst surfaces under conditions relevant to alkaline water-splitting.