Explicitly controlling electrical current density overpowers the kinetics of the chlorine evolution reaction and increases the hydrogen production during seawater electrolysis

The chlorine evolving reaction (CER) that subdues the oxygen evolving reaction (OER) during the electrolysis of seawater has long been an impediment to the attainment of producing hydrogen in volume without generating harmful byproducts containing chlorine. Using various often expensive catalysts to suppress CER and promote OER frequently requires complex chemical processes and is commonly limited to an operational electrical current density Jc of less than 1 A/cm2, which limits the production rate of hydrogen. In this paper, a new approach to suppress CER and increase the production rate of hydrogen. Two unconventional features in our approach are: the use of Jc (>10 A/cm2) much larger than those typically used (Jc <1 A/cm2) in seawater electrolysis and the use of consumable electrodes, shaped as rods of graphite. The approach allows us to safely reach an electrochemical regime wherein CER is drastically reduced, correspondingly increasing the production rate of hydrogen. Provided the core finding – CER is greatly reduced at larger Jc – in the experiment, a finite element (FE) modeling was conducted to address the question: What are the implications of using higher Jc in electrolysis? The FE modeling indicates that the substantial reduction in CER is associated with a large gradient in the electric field established between a pair of rod-shaped electrodes at higher Jc. Our study suggests that explicitly controlling Jc at a much higher level (>10 A/cm2) than conventionally used in seawater electrolysis (Jc <1 A/cm2) reduces CER to negligible levels – an environmental incentive – while potentially producing much more hydrogen per unit time – an economic incentive – than with seawater electrolysis at lower Jc.