Bubble Trouble: Quantifying the Effects of Bubbles on the Electrochemical Interface.

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Bubble accumulation is inherent in gas-evolving reactions (e.g., hydrogen evolution reaction [HER] and oxygen evolution reaction [OER]).
• These bubbles can lead to significant overpotential losses, complicating accurate experimental analysis.
• Existing literature often overstates or neglects these bubble effects, hindering reliable electrocatalyst evaluation.

Purpose of the Study:

• To systematically identify and quantify the overpotential losses induced by electrochemically produced bubbles.
• To address the inaccuracies in electrocatalyst characterization for HER and OER due to bubble effects.
• To provide a framework for mitigating these inaccuracies in gas evolution studies.

Main Methods:

• Experimental data from rotating disk electrode (RDE) measurements for HER and OER.
• Simulations utilizing a two-dimensional transmission line model.
• Quantitative analysis combining experimental and simulation results.

Main Results:

• Ohmic overpotential is identified as the dominant factor contributing to apparent activity loss caused by bubbles in RDE experiments.
• Bubble effects can lead to catalyst activity misestimates exceeding two orders of magnitude.
• Tafel slope errors can reach 100% at higher currents if bubble-induced ohmic losses are not corrected.

Conclusions:

• Electrochemical bubbles significantly impact the apparent activity and performance metrics of electrocatalysts for gas evolution reactions.
• Accurate characterization requires the explicit consideration and correction of bubble-induced ohmic overpotential losses.
• This study offers a robust methodology to improve the reliability of electrocatalyst evaluation in HER and OER.