Experimental investigation and analysis for the bubble size distribution during alkaline water electrolysis by using a wire electrode

The determination of bubble size distribution is a prerequisite for the study of gas-liquid two-phase flow characteristics in electrolytic cells. Here the departure diameter of hydrogen bubbles and oxygen bubbles and their detachment process from a nickel wire electrode during water electrolysis are studied using high-speed photography. The results show that in industrial alkaline environment, the departure diameters of most hydrogen bubbles and oxygen bubbles are generally smaller than 60 ​μm and 250 ​μm with the current density ranges from 0.15 to 0.35 ​A/cm². The adhesion force of hydrogen bubbles on a nickel wire is found to be so weak that they can separate with a tiny size. The diameters of oxygen bubbles conform to normal distribution, and its distribution range widens with the increase of current density. The theoretical analysis show that the comprehensive conversion rate of current-to-bubble is unexpectedly low especially at low current densities, which may be attributed to the loss of gas components caused by bubble detachment mode. The majority of oxygen bubbles detach by a sudden bounce after coalescence, which may bring strong disturbance to the concentration boundary layer. This also indicates the coalescence-induced bubble departure mode may occupy a dominant position in the electrolyzers.