Effects of Generated Bubbles Between Electrodes on Efficiency of Alkaline Water Electrolysis(<Special Issue>Emerging Fields in Thermal Engineering)

There is an optimum condition on water electrolysis efficiency due to the effects of generated bubbles between electrodes. In this paper, in order to explain the existence of the optimum condition, a model of alkaline water electrolysis was established. The model can express void fraction and current density profiles along electrodes, and show the existence of the optimum condition. For verification of this model, rising velocity, diameter distribution of bubbles between electrodes and current density profiles along electrodes were measured during water electrolysis of KOH solution. Two-phase flows between electrodes were observed by a still camera and a digital video camera. The results showed that bubble rising velocity ranges from 4 - 24 cm/s and becomes larger as current density increases. Bubble diameter ranges from 0.01 - 0.8 mm, where average diameter becomes large as current density increases. Obtained results showed the sound validity of present model.