Experimental study of the effect of mechanical vibration and water velocity on bubble management in PEM electrolysis cell

Abstract

The anode of a proton exchange membrane electrolysis cell (PEMEC) has a complex two-phase flow. Excessive gas concentrations tend to build up on the catalyst layer (CL) surface and inside the porous transport layers (PTLs), inhibiting electrolytic reactions from occurring. Therefore, efficient bubble management methods are required. In this paper, the principle of actions and the effect of mechanical vibration and water velocity as methods of bubble management are investigated. PEMEC bubble kinetic and two-phase flow performance were investigated using high-speed optical imaging at different amplitudes, frequencies and water velocities, and the results were correlated with electrochemical performance. The results show that the vertical sinusoidal vibration can cause cyclic compression of the PTL by the ribs, which promote the discharge of the blocked gas into the flow channel. This effect can be enhanced by increasing the amplitude of the vibration. During vibration, the inertia of the water causes the large bubbles to break up into smaller bubbles and can generate longitudinal shear forces that can promote the bubbles to detach and move. Increasing the frequency can enhance this effect by shortening the period of the action. However, the vertical sinusoidal vibration does not promote the discharge of air bubbles from the flow channel out of the cell, in which the thrust and lateral shear provided by water flow is necessary. Increasing the water velocity can also generate more bubble flow. The combination of vibration and high water velocity can significantly reduce the gas concentration in the cell. Polarization data shows a 7.2% reduction in cell polarization under the experimental conditions (80 mL/min, 1.5 mm, 150 Hz) compared to the normal state. The results of this study can provide theoretical basis and experimental data for the study of bubble management methods, optimization of working conditions and improvement of operating efficiency of PEMEC.