Bubble-driven convection induces delayed potential response in constant-current hydrogen evolution

Gas evolution during the hydrogen evolution reaction (HER) induces complex interfacial dynamics and can lead to oscillations in potential. However, the real-time coupling between bubble behavior and overpotential response remains poorly understood. In this study, we report a previously unrecognized delay phenomenon during constant-current HER: the minimum in overpotential does not coincide with the moment of bubble detachment, but instead occurs tens of milliseconds later—after a new bubble has already formed and grown to several hundred microns on the electrode surface. Using synchronized high-speed imaging and time-resolved electrochemical measurements, we show that the delay time increases consistently with current density and bubble detachment size. Statistical analysis across multiple cycles confirms strong correlations among detachment size, oscillation amplitude, and delay time. Notably, in rare cases involving successive bubble detachments, both the delay and amplitude are further amplified. Complementary CFD simulations confirm that bubble wake generates transient interfacial convection, which significantly enhances local mass transfer and temporarily reduces the concentration overpotential, thereby delaying the recovery of reaction potential even as a surface new bubble begins to grow on electrode. These findings unveil a previously unrecognized dynamic feedback mechanism in which gas bubble evolution actively modulates interfacial mass transfer, offering new insight into gas-involved electrochemical processes and a potential strategy for optimizing multiphase electrochemical systems.