Evaluation of the Potential of Zero Charge of Thin-Film (111) Platinum at the Nanoscale Using Scanning Electrochemical Cell Microscopy.

The potential of zero charge (PZC) is a key descriptor of the electrochemical interface, influencing ion distributions, mass transport, and reaction thermodynamics. It depends on the local surface structure, including grain orientation and atomic steps, making spatially resolved measurements essential. Scanning electrochemical cell microscopy (SECCM) enables local probing of electrochemical properties, including PZC. However, PZC probing via SECCM has been limited to pipette diameters above 1 µm due to low transient charging currents near the PZC, often at the instrumental detection limit. Here, PZC measurements on a Pt (111) thin film are demonstrated using submicron pipettes (~500 and ~250 nm diameters). Under conditions where the interfacial response is dominated by double-layer charging, the measured PZC is consistent with macroscale results, with values of ~0.30 V versus standard hydrogen electrode (SHE). The study reveals the impact of preconditioning, electrolyte pH, and gas atmosphere used during SECCM measurements on the recorded PZC at the nanoscale on Pt (111). In particular, variations in preconditioning potential lead to systematic shifts in both PZC and hydrogen evolution reaction (HER) activity, reflecting the correlation between both properties. Overall, this work establishes a robust experimental protocol for PZC mapping at the submicron scale using SECCM.