Experimental and numerical analysis of the growth, detachment and coalescence of oxygen bubbles on the electrode surfaces in alkaline water electrolysis

Alkaline water electrolysis has been attracting attention as a method of hydrogen production due to its cost-effectiveness and stability. One of the disadvantages of alkaline water electrolysis is low current density caused by oxygen bubbles evolving on the electrode surfaces. To improve the efficiency of alkaline water electrolysis, a better understanding of bubble behavior on the electrode surfaces, including bubble growth and detachment, is required. While several numerical simulations of bubble behavior have been reported, further investigation is needed to obtain appropriate boundary conditions on the electrode surfaces. In this study, bubble behavior on a nickel electrode in KOH aqueous solution was observed to gain insight into the boundary conditions on the electrode surfaces. We fabricated electrodes with widths of a sub-millimeter scale to observe the growth, detachment and coalescence of bubbles. The time evolution of the diameter, contact angle, and contact area of bubbles on the electrode surface were measured using a high-speed camera. Moreover, numerical simulations of bubble detachment on the electrode surfaces were performed and compared with the experimental results.