Gas bubble removal in alkaline water electrolysis with utilization of pressure swings

Abstract

The energy consumption in hydrogen production through water electrolysis remains a major bottleneck for practical application. Gas bubbles that inevitably form during water electrolysis significantly increase the overall cell resistance; thereby reducing the energy efficiency. This added bubble resistance may be mitigated by enhancing the bubble removal in the system. In this work, we study the accelerated growth and detachment process of gas bubbles on electrodes, i.e. the screening layer, via pressure swings. The influence of these pressure swings on the cell voltage was experimentally investigated, by imposing temporarily low system pressure. We demonstrate that pressure swings are a means to compensate the cell voltage accumulation caused by the screening layer build up (i.e. a relaxation process). A reduction of approximately 0.1 V is realized this way, with the largest energy saving when a pressure swing is applied every 100–300 s (equivalent to a cumulative H2 production of 0.03–0.09 mmol/cm2). The reduction of cell voltage due to pressure swings increases nearly linearly with increasing current density. Furthermore, investigation of the voltage-time curves indicates a synergistic effect between bubbles for its release. It is concluded that the pressure swings are a means to effectively remove gas bubbles from the screening layer.