Life beyond Fritz: On the detachment of electrolytic bubbles

TL;DR

This study investigates hydrogen bubble detachment during electrolysis, revealing that contact line hysteresis significantly influences bubble departure size, especially at higher acid concentrations, challenging classical predictions.

Contribution

It introduces a detailed experimental analysis of bubble detachment modes, highlighting the role of contact line hysteresis and providing a new predictive model for departure radius.

Findings

Spreading bubbles become more common at higher HClO4 concentrations.

Departure radius exceeds classical Fritz prediction due to contact line hysteresis.

A new model accurately predicts bubble departure size based on contact angles.

Abstract

We present an experimental study on detachment characteristics of hydrogen bubbles during electrolysis. Using a transparent (Pt or Ni) electrode enables us to directly observe the bubble contact line and bubble size. Based on these quantities we determine other parameters such as the contact angle and volume through solutions of the Young-Laplace equation. We observe bubbles without ('pinned bubbles') and with ('spreading bubbles') contact line spreading, and find that the latter mode becomes more prevalent if the concentration of HClO4 is greater than or equal to 0.1 M. The departure radius for spreading bubbles is found to drastically exceed the value predicted by the well-known formula of W. Fritz (Physik. Zeitschr. 1935, 36, 379-384) for this case. We show that this is related to the contact line hysteresis, which leads to pinning of the contact line after an initial spreading phase at the receding contact angle. The departure mode is then similar to a pinned bubble and occurs once the contact angle reaches the advancing contact angle of the surface. A prediction for the departure radius based on these findings is found to be consistent with the experimental data.