Performance Enhancement of Electrocatalytic Hydrogen Evolution through Coalescence-Induced Bubble Dynamics

Abstract

The evolution of electrogenerated gas bubbles during water electrolysis can significantly hamper the overall process efficiency. Promoting the departure of electrochemically generated bubbles during (water) electrolysis is therefore beneficial. For a single bubble, a departure from the electrode surface occurs when buoyancy wins over the downward-acting forces (e.g., contact, Marangoni, and electric forces). In this work, the dynamics of a pair of H 2 bubbles produced during the hydrogen evolution reaction in 0.5 M H 2 SO 4 using a dual platinum microelectrode system is systematically studied by varying the electrode distance and the cathodic potential. By combining highspeed imaging and electrochemical analysis, we demonstrate the importance of bubble−bubble interactions in the departure process. We show that bubble coalescence may lead to substantially earlier bubble departure as compared to buoyancy effects alone, resulting in considerably higher reaction rates at a constant potential. However, due to continued mass input and conservation of momentum, repeated coalescence events with bubbles close to the electrode may drive departed bubbles back to the surface beyond a critical current, which increases with the electrode spacing. The latter leads to the resumption of bubble growth near the electrode surface, followed by buoyancy-driven departure. While less favorable at small electrode spacing, this configuration proves to be very beneficial at larger separations, increasing the mean current up to 2.4 times compared to a single electrode under the conditions explored in this study.

In Situ Observation and Electrical Signal Analysis of Different Bubble Detachment Modes on Microelectrode Surface

“…In the current studies on bubble evolution using microelectrodes, there are many reports on the effect of voltage on bubble evolution. 9,[16][17][18][19] However, there are fewer studies on the evolutionary behavior of bubbles at different current densities. Studies for current densities have focused on flat electrodes with large areas.…”

“…Lu et al 49 investigated the effect of surfactant on the Marangoni force and concluded that the addition of surfactant reduced the Marangoni force on the bubbles. Existing studies 17,23,50,51 focus on the bubble dynamics of single bubbles. However, there are fewer studies on the electrochemical parameters during bubble evolution, and the effect of surfactant concentration on the additional resistance caused by bubble covering remains unclear.…”