Computational Model of Two-Phase Mass Transport Dynamics for pH-Buffered Hydrogen Evolution Reactions in Porous Electrodes

Abstract

Neutral/near-neutral water electrolysis is promising to reduce the overall cost of industrial hydrogen production. However, the current studies rarely concern the coupled interactions among the chemical/electrochemical reactions and two-phase mass transport during the hydrogen evolution reaction (HER) in the porous electrode. In this work, the geometry of a porous electrode is developed through a random growth method, and the mathematical model is then incorporated into the geometrical model to systematically investigate the interplay among these diverse processes. The developed model is solved to examine velocity and concentration profiles under various conditions. The study shows that the buffer concentration has a much more remarkable effect (117% increase in current density) on the HER performance compared to velocity (24% increase in current density). In addition, the electrode with a flow-through mode delivers a 164% higher HER current density than that with flow-by mode due to the prompted mass transport of ions and bubbles. Furthermore, the comparison study suggests that the electrode in acetic acid buffer delivers the lowest pH polarization, thereby minimizing the mass transport loss during the HER and achieving a 53% improvement in HER performance compared to that in other buffers. These results indicate that the mass transport of buffer species and bubbles in the pores of the electrode can significantly improve the HER performance. This paper concludes that the developed model can provide some guidance for the design of a porous electrode and the selection of buffer for the HER, finally advancing the understanding of the fundamental mechanisms in the buffered HER of the porous electrode.