Life beyond\nFritz: On the Detachment of Electrolytic\nBubbles

We present an experimental\nstudy on detachment characteristics\nof hydrogen bubbles during electrolysis. Using a transparent (Pt or\nNi) electrode enables us to directly observe the bubble contact line\nand bubble size. Based on these quantities we determine other parameters\nsuch as the contact angle and volume through solutions of the Young–Laplace\nequation. We observe bubbles without (“pinned bubbles”)\nand with (“spreading bubbles”) contact line spreading\nand find that the latter mode becomes more prevalent if the concentration\nof HClO<sub>4</sub> is ≥0.1 M. The departure radius for spreading\nbubbles is found to drastically exceed the value predicted by the\nwell-known formula of W. Fritz [<i>Phys. Z.</i> <b>1935</b>, <i>36</i>, 379–384] for this case. We show that\nthis is related to the contact line hysteresis, which leads to pinning\nof the contact line after an initial spreading phase at the receding\ncontact angle. The departure mode is then similar to a pinned bubble\nand occurs once the contact angle reaches the advancing contact angle\nof the surface. A prediction for the departure radius based on these\nfindings is found to be consistent with the experimental data.