Raising the curtain: Bubble size measurement inside parallel plate electrolyzers

Abstract

Alongside vertical gas-evolving electrodes, gas bubbles nucleate, grow, coalesce, detach, and ultimately form a bubble curtain, affecting the fluid dynamic, electrochemical reaction, mass transport, and ohmic drop. Due to the small inter-electrode gap in parallel plate electrolyzers, the size determination of detached bubbles inside the bubble curtain close to the electrodes is challenging. In particular, the size determination of detached oxygen bubbles needs to be addressed. We present an optical setup to record images from detached oxygen bubbles inside the bubble curtain of a membrane-separated, parallel plate electrolyzer. The images are postprocessed using an adopted region-based convolutional neuronal network to quantify the bubble sizes. Next, the electrolyte flow velocity, concentration, current density, and catalysts are varied, and the effect on the oxygen bubble size distribution is studied. The median size ranges from 140 to ▪, doubling values from literature measured in artificial electrolyzers.