Influence of hydrodynamic parameters on the critical current density at water electrolysis: Mass flux, channel inclination and inlet void fraction

Abstract

Hydrogen production rate increases as current density increases in a water electrolysis. At a certain high current density, the cell potential abruptly increases due to the hydrogen film formed at the cathode, which is known as the critical current density (CCD). Hence, it is imperative to increase the CCD for effective hydrogen production. However, the investigations regarding hydrodynamic parameters, which affect the CCD have hardly been performed. This work investigated the influence of the hydrodynamic parameters such as mass flux, inclination of cathode channel and inlet void fraction on the CCD in water electrolysis. The increase in the mass flux increased the CCD regardless of the channel inclination and the inlet void fraction due to the enhanced hydrogen bubble elimination near the surface, which retards hydrogen film formation. The influence of the inlet void fraction showed different trend according to the channel inclination. Monotonically decreasing trend was measured in the vertical channel due to reduced flow rate near the surface as the void fraction increased. Meanwhile, a peak was measured in the inclined channels. The inlet voids at bubbly flow regime dispersed the hydrogen bubbles from the cathode, while those at the slug flow regime aided and enhanced the hydrogen film formation at the cathode. It is concluded that the inlet void fraction either enhances or impairs the CCD depending on the flow regime. The authors expect that this work would shed light on the roles of hydrodynamic parameters for efficient hydrogen production.