Electrolyte spraying within H$_2$ bubbles during water electrolysis

TL;DR

This study reveals how electrolyte droplets are sprayed within hydrogen bubbles during electrolysis, affecting bubble dynamics and efficiency, with implications for optimizing electrochemical systems and understanding related phenomena.

Contribution

It uncovers a novel transport mechanism involving electrolyte droplet coalescence with microbubbles during hydrogen evolution, including effects of Marangoni convection and interface mobility.

Findings

Electrolyte droplets are driven into bubbles by coalescence during hydrogen evolution.

Droplet spray influences bubble detachment and electrode contact dynamics.

Findings are relevant for optimizing electrolysis and understanding jet formation in various processes.

Abstract

Electrolytically generated gas bubbles can significantly hamper the overall electrolysis efficiency. Therefore it is crucial to understand their dynamics in order to optimise water electrolyzer systems. Here we demonstrate a distinct transport mechanism where coalescence with microbubbles drives electrolyte droplets, resulting from the fragmentation of the Worthington jet, into the gas phase during hydrogen evolution reaction, both in normal and microgravity environments. This indicates that the H$_2$ bubble is not only composed of hydrogen gas and vapor but also includes electrolyte fractions. Reminiscent of bursting bubbles on a liquid-gas interface, this behavior results in a flow inside the bubble, which is further affected by Marangoni convection at the gas-electrolyte interface, highlighting interface mobility. In the case of electrode-attached bubbles, the sprayed droplets form electrolyte puddles at the bubble-electrode contact area, affecting the dynamics near the three-phase contact line and favoring bubble detachment from the electrode. The results of this work unravel important insights into the physicochemical aspects of electrolytic gas bubbles, integral for optimizing gas-evolving electrochemical systems. Besides, our findings are essential for studying the limits of jet formation and rupture relevant to acid mist formation in electrowinning, generation of sea spray aerosols, impact of droplets on liquid surfaces, etc.