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.