Electrolysis-Driven and Pressure-Controlled Diffusive Growth of Successive Bubbles on Microstructured Surfaces

Area of Science:

• Electrochemistry
• Materials Science
• Fluid Dynamics

Background:

• Efficient water-splitting and chemical reactors depend on controlling bubble growth dynamics on electrodes.
• Understanding hydrogen (H2) bubble formation is crucial for optimizing energy efficiency in electrochemical devices.

Purpose of the Study:

• To investigate the diffusion-driven growth dynamics of successive H2 bubbles generated at a controlled nucleation site on a silicon electrode.
• To analyze the impact of gas depletion from previous bubbles, parasitic bubble formation, and cavity effects on H2 bubble growth.
• To compare the growth dynamics of H2 bubbles during electrolysis with CO2 bubbles in a supersaturated solution.

Main Methods:

• Utilizing controlled nucleation via a hydrophobic micropit on a micrometer-sized pillar.
• Conducting constant-current electrolysis experiments (5-15 A/m2).
• Employing numerical simulations to analyze bubble growth and gas depletion effects.

Main Results:

• Observed a stagnation regime followed by rapid growth and steady state for successive H2 bubbles, contradicting constant growth rate assumptions.
• Identified significant gas depletion from prior bubbles, sidewall bubbles, and the electrode cavity.
• Demonstrated a successive decrease in the growth coefficient for CO2 bubbles due to persistent CO2 depletion.

Conclusions:

• Electrolytic H2 bubble growth rates are dynamic and non-invariant under constant current, influenced by complex depletion mechanisms.
• The growth dynamics of H2 bubbles differ significantly from CO2 bubbles, highlighting the importance of specific gas and electrolyte conditions.
• Findings challenge conventional understanding and provide insights for designing more efficient electrochemical reactors.