Solving The Green Hydrogen Water Problem With Seawater

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Last Updated on: 13th April 2025, 11:28 am

The math is not adding up for the global green hydrogen industry. The electrolyzers that push hydrogen gas from water are expensive, and they also have a water problem. They can’t use just any old water. They need clean water, and that puts the industry up against an estimated 4 billion people who already lack adequate supplies of potable water. That’s where seawater comes in….

The Seawater Solution For Green Hydrogen

Under the current state of electrolysis technology, the rule of thumb is 9 liters of clean water to produce 1 kilogram of green hydrogen. Some analysts anticipate that green hydrogen demand could total 500 million metric tons (or more) per year by 2050, a figure that would require 4.5 trillion liters of clean water to produce. With an estimated 4 billion people in the world experiencing water scarcity, that’s not a particularly sustainable scenario.

Using seawater to produce green hydrogen is one obvious alternative, but it has to be purified, and that takes money. The leading Chinese energy firm Sinopec is among those exploring an alternative pathway that involves engineering new electrolyzers that are hardy enough to deploy directly on seawater.

That takes money, too. However, direct seawater electrolysis could be the winning ticket, at least for some applications. Sinopec has already deployed other electrolysis systems in China, including a megawatt-scale PEM (proton exchange membrane) electrolyzer and the first 100-kilowatt solid oxide project in China. Last December, it completed a pilot-scale R&D project to explore direct saltwater electrolysis at its Qingdao Refinery in Shandong Province, which sits on the Yellow Sea.

“Seawater contains approximately 3% salt, and impurities, such as chloride ions, can corrode electrolytic electrodes, while cation deposits may clog equipment channels, reducing efficiency and causing damage,” Sinopec points out.

Sinopec lists chlorine-resistant electrode technology and a high-performance electrode plate among the improvements to the Qingdao electrolysis system, which was developed in collaboration with the Dalian Institute of Petroleum and Petrochemicals. The system runs on electricity from an existing floating solar array that also provides electricity to the refinery.

Green Hydrogen And The “Trifecta Of Sustainability”

Sinopec anticipates that its direct seawater electrolysis system can also be applied to extract green hydrogen from industrial wastewater, further reducing the demand on freshwater resources.

In terms of proactively helping to solve water scarcity issues, though, the direct electrolysis approach doesn’t help much. Whether seawater or industrial waste, non-potable water goes into the electrolysis system, and non-potable water comes out.

Last week, Cornell University reported on a compromise approach, developed in collaboration with MIT, Johns Hopkins University, and Michigan State University, calling it the “trifecta of sustainability technology.”

The Cornell-lead study describes a solar-powered seawater electrolysis system that deploys the solar panels for double duty. In addition to providing electricity to run the system, the solar panels provide waste heat to run a distillation process that yields potable water.

“Most PV cells can only convert up to approximately 30% of solar energy into electricity, and the rest dissipates as waste heat. But the team’s device is able to harness most of that waste heat and uses it to warm the seawater until it evaporates,” Cornell notes.

How Does It Work?

“Basically, the short-wavelength sunlight interacts with the solar cell to generate electricity, and the longer wavelength light generates the waste heat to power the seawater distillation,” explains Lenan Zhang, an assistant professor in at Cornell Engineering and leader of the research project.

“This way, all the solar energy can be fully used. Nothing is wasted,” Zhang emphasizes.

To achieve the thermal evaporation side of the process, the researchers engineered the surface of their solar panel to trap a thin layer of seawater with each passing, enabling them to increase evaporation efficiency by 90%. After the water vapor condenses, it goes to the electrolyzer.

If you’re thinking the seawater also provides a cooling effect that improves the conversion efficiency of the solar panels, that could also be in the cards. For now, though, Zhang and his team are focused on bringing down the cost of green hydrogen. Compared to a benchmark of $10.00 per kilogram, they are aiming at $1.00.

That’s the short version. The research team published the long version, with Xuanjie Wang of MIT as lead author, in the journal Energy and Environmental Science under the title, “Over 12% efficiency solar-powered green hydrogen production from seawater.”

“With natural sunlight and real seawater as the sole inputs, we experimentally demonstrate a 12.6% solar-to-hydrogen conversion efficiency and a 35.9 L m⁻² h⁻¹ production rate of green hydrogen under one-sun illumination, where additional 1.2 L m⁻² h⁻¹ clean water is obtained as a byproduct,” they summarized.

More Renewable Energy For Green Hydrogen

Experimental work aside, some green hydrogen projects are already incorporating conventional seawater desalination to fulfill their water requirements. Egypt and France, for example, have just reached a handshake agreement on a new €7 billion green hydrogen project supported by a dedicated desalination facility, to be constructed near Ras Shokeir on the Red Sea coast, under the umbrella of the French firm EDF Renewables.

The electrolysis system will be powered by nearby wind and solar farms, which will presumably also service the desalination facility.

Ocean waves could provide another coastal source of renewable energy for desalination facilities. The global wave energy industry has been slow to achieve commercial application, but activity has picked up in recent years and the US Department of Energy is among those exploring the potential for applying it to desalination.

Last year, the Energy Department awarded funding to two projects that combine wave energy with desalination systems. The immediate aim is to help reduce the expense of desalination for coastal communities facing water scarcity, but purifying water for green hydrogen is among the other potential uses.

One of the projects is fairly straightforward. A research team at Purdue University will use their grant to develop an energy efficient wave-powered, pumpless desalination system based on hydraulics instead of electricity.

Researchers at the University of Minnesota are tasked with the other project, called “Hydraulic Switch-Mode Power Transformer Power-Take Off for Wave-Powered Reverse Osmosis Desalination.” If all goes according to plan, the system will deploy wave energy for dual uses. “The power take-off system converts the power from waves to generate electricity and generates direct hydraulic pressure to produce clean drinking water,” the Energy Department explains.

“The wave-powered desalination system can operate independently and with minimal disruptions by having this dual capability to generate electricity and hydraulic pressure and can power other auxiliary processes and systems in utility-scale desalination plants,” they add.

Here’s hoping. The malevolently incompetent Commander-in-Chief who occupies the White House keeps finding new ways to keep the US from exercising its best self, but innovators elsewhere around the world are under no such burden.

Photo: Electricity from a floating solar in China array powers an experimental electrolysis system that produces green hydrogen directly from seawater (courtesy of Sinopec via prnewswire).