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The team uses a concentrated potassium hydroxide electrolyte solution to immerse the electrodes, and a porous membrane helps separate the electrolyte solution from seawater. The fluorine-containing membrane blocks liquid water but allows water vapor to pass through.
During electrolysis, the water in the electrolyte solution is spitted into its constituent components. This results in a pressure difference between the electrolyte and the seawater, causing the seawater to evaporate. At the same time, water passes through the membrane into the electrolyte and turns back into liquid water, replenishing the stock for the next cycle.
“Importantly, this configuration and mechanism hold promise for further applications in simultaneous water-based effluent treatment and resource recovery and hydrogen production in one step.”
The researchers are positive that their device will be able to produce hydrogen as well as recover lithium from seawater. Further applications of the device extend to activities such as industrial freshwater cleaning.
Summary
Electrochemical salt water electrolysis using renewable energy as input is a highly desirable and sustainable method for large-scale production of green hydrogen; However, its practical feasibility is severely challenged by insufficient durability due to electrode side reactions and corrosion issues arising from the complex constituents of seawater. Although catalytic engineering using polyanion coatings to suppress corrosion by chloride ions or to fabricate highly selective electrocatalysts has been extensively exploited with modest success, it is still not satisfactory for practical applications. Indirect seawater fractionation using a pre-desalination process can avoid side-reaction and corrosion problems, but requires additional energy input, making it less attractive economically. In addition, the independent bulk desalination system makes seawater electrolysis systems less flexible in terms of size. Here we propose a direct seawater electrolysis method for hydrogen production that fundamentally addresses the side-reaction and corrosion problems. A demonstration system was operated stably at a current density of 250 milliamperes per square centimeter for over 3,200 hours under practical application conditions without failure. This strategy realizes efficient, size-flexible and scalable direct seawater electrolysis in a manner similar to freshwater fractionation without a significant increase in operating cost, and has high potential for practical application. Importantly, this configuration and mechanism holds promise for further applications in simultaneous water-based effluent treatment and resource recovery and hydrogen production in one step.
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