Zongping Shao, a chemical engineering professor at China’s Nanjing Tech University, led the team that published their research on a device that splits salty seawater to produce hydrogen directly. The device, a membrane-based seawater electrolyzer, was published in the journal Nature, and the researchers claimed that their model ran for over 3,200 hours without failure under practical application conditions.
Drawbacks of old methods
The majority of hydrogen produced today is derived from fossil fuels, which increases the carbon footprint significantly. Salt water’s properties cause corrosion of electrodes for use in various systems, rendering them inoperable. The use of polyanion coatings to resist corrosion by chloride ions or highly selective electrocatalysts has not aided practical applications sufficiently. A desalination process can solve the problem, but it requires more energy, making it less economically appealing. The size of the equipment used in the desalination process also limits the flexibility of such solutions.
New proposed technology
An electrolyzer is typically made up of two electrodes coated with catalysts, separated by a membrane that separates the constituent components – hydrogen and oxygen. The formation of highly corrosive chlorine gas during the process causes catalysts and electrodes to degrade more quickly. Seawater ions such as magnesium and calcium can also clog the membranes. These elements reduce the overall efficiency and lifespan of such devices.
The electrodes are dipped in a concentrated potassium hydroxide electrolyte solution, and a porous membrane helps separate the electrolyte solution from seawater. The fluorine-rich membrane prevents liquid water from passing through while allowing water vapour to pass through.
Water in the electrolyte solution is split into its constituent components during electrolysis. This causes a pressure difference between the electrolyte and the seawater, which causes the latter to evaporate. Simultaneously, water passes through the membrane into the electrolyte and returns to liquid water, replenishing the stock for the next cycle.
The researchers are confident that their device will be able to recover lithium from seawater in addition to producing hydrogen. The device’s additional applications include cleaning industrial freshwater.
