Scientists have found an ingenious way to generate hydrogen gas directly from salty seawater. If renewable energy powers the process, it could be another step toward a clean energy future.
The new device makes some chemical tweaks to existing technology, making it possible to extract hydrogen from untreated, unpurified seawater — which could allay concerns about using precious water sources.
“We split natural seawater into oxygen and hydrogen … to produce green hydrogen by electrolysis using non-precious and cheap catalysts in commercial electrolyzers,” explained chemical engineer Qiao Shizhang at the University of Adelaide in Australia.
Traditionally, hydrogen fuel is made from natural gas, but it can also be made through electrolysis.
Electrolysis is a water splitting reaction that uses electrical energy to separate hydrogen atoms from elbow-shaped water molecules, and the electrolyzer is the device in which this happens.
Now, the process can be done using electricity from fossil fuels or renewable sources, but both systems require fresh water. Finding a way to achieve electrolysis with seawater could make the future of green hydrogen fuel production more sustainable.
Concerned about water scarcity, researchers have been trying to develop an alternative to commercial electrolyzers that can only use pure fresh water.
Accessible freshwater accounts for only 1% of the Earth’s total water volume, but available seawater is almost unlimited.
While concerns about water scarcity are justified, recent estimates suggest that the amount of water needed to sustain future hydrogen use is far less than the trillions of liters of water used to extract and burn fossil fuels today.
Still, scientists are concerned about the environmental impact. They have been trying to develop devices to produce hydrogen from seawater for decades, but have run into several obstacles.
When placed in an electrolyzer, unwanted chloride ions in seawater corrode the catalyst material, which drives the hydrogen-producing, water-splitting reaction. Large amounts of insoluble precipitates can also form, clogging reaction sites and hindering large-scale production.
The new system developed by Joe and colleagues avoids both problems.
As they describe in their new paper, the researchers layered a hard Lewis acid substance over a range of common cobalt oxide catalysts to split water molecules. In a series of tests, the modified catalyst resisted chlorine gas attack and prevented any deposits from forming.
“This is a general strategy that can be applied to different catalysts without the need for specially designed catalysts and electrolyzer designs,” the researchers wrote in their published paper.
While that sounds promising, the decades-long effort to develop seawater electrolyzers should serve as a reminder of the challenges of commercializing this technology, or any other.
“Direct seawater electrolysis without purification processes and chemical additives is very attractive and has been researched for about 40 years, but the main challenges of this technology remain in terms of catalyst engineering and equipment design,” the researchers note.
Recent progress has been encouraging, and the new device is one of many promising attempts to generate hydrogen from seawater.
For example, scientists from China and Australia recently developed a prototype device designed to float on the surface of the ocean and use solar energy to separate hydrogen from seawater. Another prototype in the works takes a completely different approach, harvesting water from humid air before extracting the hydrogen.
Of course, prototyping is a far cry from an industrial-scale approach, so it’s best to do a healthy mix of potential systems in a pipeline to see which ones deliver.
Joe and his colleagues are working on expanding their system by using larger electrolyzers. But many factors can make or break a potential technology.
Commercialization of any process comes down to material costs, energy inputs, and efficiencies at scale—where small gains can have a huge impact on how much hydrogen can be produced.
Cobalt, a material used in metal oxide catalysts, is not without its problems. As with any precious metal used in batteries or solar panels, it must be sustainably mined and recycled where possible.
After testing the durability of their device, Joe and colleagues think their modified catalyst could go even further. Their system can provide similar output to commercial electrolyzers at the same low temperature and operating conditions.
But with other researchers making strides in steadily improving the efficiency of conventional electrolyzers, it’s really anyone’s game.
The study was published in natural energy.
