Bubble Formation in the Electrolyte Triggers Voltage Instability in CO ₂ Electrolyzers

Summary

The electrochemical reduction of CO ₂ is promising for mitigating anthropogenic greenhouse gas emissions; however, voltage instabilities currently inhibit reaching high current densities that are prerequisite for commercialization. Here, for the first time, we elucidate that product gaseous bubble accumulation on the electrode/electrolyte interface is the direct cause of the voltage instability in CO ₂ electrolyzers. Although bubble formation in water electrolyzers has been extensively studied, we identified that voltage instability caused by bubble formation is unique to CO ₂ electrolyzers. The appearance of syngas bubbles within the electrolyte at the gas diffusion electrode (GDE)-electrolyte chamber interface (i.e. ∼10% bubble coverage of the GDE surface) was accompanied by voltage oscillations of 60 mV. The presence of syngas in the electrolyte chamber physically inhibited two-phase reaction interfaces, thereby resulting in unstable cell performance. The strategic incorporation of our insights on bubble growth behavior and voltage instability is vital for designing commercially relevant CO ₂ electrolyzers.

Graphical Abstract

Highlights

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  X-ray imaging was used to characterize the bubble formation in a CO ₂ electrolyzer

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  Gas formed near the GDE-electrolyte chamber interface and caused voltage instabilities

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  We hypothesize that gas physically inhibits two-phase reaction interfaces

Abstract

Electrochemical Energy Production; Mechanical Engineering Interfacial Electrochemistry