Measuring Transient Interfacial pH Changes With Rotating Ring–Disk Electrochemistry: Theory and Experimental Considerations

Understanding interfacial pH dynamics is essential for elucidating proton–coupled electron transfer (PCET) mechanisms in electrocatalysis, yet direct and quantitative measurements remain challenging. Rotating ring–disk electrochemistry (RRDE), using the ring to sense local pH changes at the disk, has emerged as a powerful approach due to its seemingly straightforward experimental setup and high sensitivity. Still, a full theoretical perspective that captures the transient nature of the ring response and provides predictive experimental guidelines remains underdeveloped. Here, we provide a simulation framework that captures both steady–state and transient pH evolution in RRDE across various alkaline electrolytes. However, comparison with experimental results, particularly at low rotation rates, reveals substantial deviations from theory. To investigate this discrepancy, we performed electrostatic simulations, showing that ohmic ( iR ) potential drops in the electrolyte induce disk–ring electrical cross–talk, often producing ring responses that mimic true pHinduced changes. Moreover, the magnitude of this coupling scales linearly with the uncompensated solution resistance, indicating that the measured ring response originates from iR– mediated potential perturbations. We propose strategies to mitigate these artifacts, including optimized measurement protocols and strategic reference–electrode placement using a Luggin capillary. Together, these results enable a clearer separation of pH dynamics from solution–resistance artifacts in RRDE studies.