To address this challenge, a flow cell was designed with an internal nozzle that directs a high-velocity jet of electrolyte across the working electrode surface. The flowing electrolyte suppresses bubble nucleation by lowering the local concentration of dissolved species and removes existing bubbles through shear forces, thereby preserving a clear optical path for spectroscopy.
High speed videography and imaging were used to visualize the bubble coverage of hydrogen on a platinum electrode across a range of current densities and flow rates. Quantitative image analysis revealed a substantial decrease in bubble coverage under flowing conditions compared to the stagnant electrolyte. To understand the underlying mechanisms behind the flow cell, a mass-transport model was developed to correlate local hydrogen concentration and flow rate to bubble coverage. The model identified the critical supersaturation limit for bubble formation.
To test the effectiveness of the flow cell during HER conditions, a graphene-platinum electrode was studied in stagnant electrolyte and flowing conditions (100 mL/min). The graphene’s 2D and G bands were observable at current densities reaching 25 mA cm-², significantly surpassing the limit of 1 mA cm-² in stagnant conditions. Overall, this work establishes a generalizable approach for obtaining in situ optical measurements during electrochemical reactions under high-current-density operating conditions.