Two-phase electrolysis process modelling: from the bubble to the electrochemical cell scale

Abstract

During two-phase electrolysis for hydrogen, aluminium or fluor production, there are bubbles which are created at electrodes which imply a great hydrodynamic acceleration but also quite important electrical properties and electrochemical processes disturbance. There are few works concerning the local modelling of electrochemical processes during a two-phase electrolysis process. Nevertheless, effects like the anode effect, particularly expensive on the point of the process efficiency, should need a better understanding. The goal of the present work is to present the modelling and the numerical simulation of the gas production, from the single bubble scale to the macroscopic electrochemical cell, during the two-phase electrolysis process. Bubbles are motion sources for the electrolysis cell flow, and then hydrodynamic properties are strongly coupled with species transport and electrical performances. The presence of bubbles modifies these global and local properties: the electrolysis cell and the current density distribution are modified. The present work shows theoretical modelling on both scales and also performance changes during the two-phase electrolysis processes.

Multiphysics Model of a Fluorine Electrolysis Cell

“…The current conservation equations are used : …”

Polarization curves for an alkaline water electrolysis at a small pin vertical electrode to produce hydrogen

“…After point C, the mean current decreases sharply. This is associated to the surface and volume screening roles of bubbles which have led to a continuous gaseous film around the working electrode 13–20. The electro‐active area fraction screened by the adhering bubbles is defined as θ, whereas the bubble volume fraction in the surrounding electrolyte is noted ε.…”

“…Many researchers1–15 have studied and exposed the difficulties in the two‐phase electrolysis processes. The main problem is the existence of numerous effects, at the bubble scale but as well at the macroscopic electrochemical cell or reactor scale.…”

“…The stagnant electrolyte is rigorously obtained in absence of forced flow and gravity to avoid natural convection. This implies the interest in zero gravity experiments of many scientists 7–14…”

“…This has a local impact and also a global one in the case of confined electrochemical reactors. The motion source near an electrode is transported in the reactor domain 12–15…”