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Limitless Supply of Seawater to Help Accelerate the Transition to Green Hydrogen

Much of the activity in the green hydrogen field is centered around electrolysis systems that jolt hydrogen gas from water with an electrical current, sourced from renewables like wind or solar. Most current electrolysis technologies require purified water, but innovations involving seawater open up new possibilities.
By Tina Casey
people surfing in the ocean with city skyline in the background - gold coast australia - technology to turn seawater into green hydrogen

Hydrogen is ubiquitous throughout industrialized economies, filling needs in a wide variety of industries from refining and metallurgy to agriculture and personal care products. Even as these industries attempt to decarbonize, hydrogen holds them back, because fossil fuels are the primary source of the global hydrogen supply. Fortunately, more sustainable alternatives are finally emerging. Now, the race is on to displace fossil energy with green hydrogen produced from renewable resources.

Green hydrogen from seawater

Much of the activity in the green hydrogen field is centered around electrolysis systems that jolt hydrogen gas from water with an electrical current, sourced from wind, solar or other renewable resources. 

Electrolysis is not a new technology, but its application to commercial-scale hydrogen production is a recent phenomenon, and innovation in the field is still ongoing.

One key challenge involves water resources. Under the current state of the technology, electrolysis requires purified water. That can raise a red flag, as global freshwater resources are already stretched thin. However, according to some analyses, this amounts to water savings overall as green hydrogen displaces fossil-based energy systems that use even more water. Green hydrogen also compares favorably to nuclear energy in terms of water use.

In addition, recent improvements in electrolysis technology opened the door to using seawater instead of freshwater. Researchers are working to lower costs by eliminating the purification steps without exposing the system to corrosion and other damage caused by seawater.

One recent breakthrough, published in the journal Nature earlier this year, demonstrates that hydrogen can be coaxed directly from seawater, yielding results similar to that of using purified water.

Green hydrogen, now with carbon capture

Another variation of seawater-based electrolysis was developed by the U.S. startup Equatic. The company’s green hydrogen system captures and converts airborne carbon into a solid form, drawing on the natural chemistry of seawater. 

“Seawater has contained dissolved inorganic carbon for millions of years, and is in effect oversaturated with respect to calcium carbonate (as exemplified by the stability of sea shells),” the company's website reads. “The Equatic process exploits this fact to immobilize carbon dioxide in the oceans for tens of thousands, if not millions of years.”

The Equatic green hydrogen system is a closed process that takes place within an industrial-type facility, which allows for precise monitoring to ensure that seawater is returned to the ocean in its original condition with no acidification.

“We say we make green hydrogen,” Equatic COO Edward Sanders told TriplePundit. “But our [green hydrogen] is actually carbon negative. For every ton of carbon dioxide we take out, we make 4.5 kilograms of hydrogen. We can either sell it for revenue, or we can use it to power our process in a fuel cell.”

The sustainable limestone economy of the future

Equatic is focused primarily on marketing its system as a low-cost, energy-efficient, carbon-negative source of green hydrogen. However, the potential to harvest bicarbonate solids from the system raises some interesting possibilities for carbon recycling.

Sanders suggested that using carbon solids in support of climate adaptation would be one good place to start. For example, calcium carbonate is more commonly known as limestone, the main ingredient in Portland cement. 

In addition to cement-making, limestone has many other applications throughout the global economy. Calcium carbonate is an important source of calcium oxide, which plays a role in industries like steel, glass and paper manufacturing. Calcium oxide is also used to treat water and purify sugar, among other applications.

Considering the potential for environmental and health impacts involved in limestone mining, a non-mined supply of calcium carbonate would be a valuable resource for manufacturers that are seeking to align their supply chains with ESG (environmental, social and governance) principles.

Scaling up for the green hydrogen economy

With or without a market for carbon solids, the demand for green hydrogen is growing at an explosive rate, providing Equatic with the opportunity to scale up rapidly.

“The ultimate scale we need to get to on carbon dioxide removal is gigaton-scale. At that scale, we could decarbonize entire industries with green hydrogen,” Sanders said.

Equatic described its plans for carbon capture with hydrogen production in a press announcement last month, which notes that the company spun out of research at the University of California Los Angeles Institute for Carbon Management, with $30 million in private- and public-sector financial support.

Two Equatic systems are up and running at a demonstration scale. One is located at the Port of Los Angeles, as part of the port’s longstanding support for low-carbon initiatives. The other system is located in Singapore, where a commercial-scale system is also in the planning stages.

The carbon removal at both of the demonstration locations is fully subscribed through the revenue platform Stripe. A newly announced pre-purchase option agreement with Boeing will also help accelerate Equatic’s transition to a commercial scale.

The agreement calls for the delivery of 2,100 metric tons of carbon-negative green hydrogen to Boeing, which will involve removing 62,000 metric tons of carbon dioxide. That brings Equatic a significant step closer to its interim goal of removing 100,000 metric tons of carbon dioxide per year. By 2028, the company expects to bump its carbon removal up to millions of metric tons per year.

Equatic is just one example of innovation in the green hydrogen field. There are others, such as the use of photoelectrochemical cells to mimic the natural process of photosynthesis. As a group, these developments are pushing down the cost of sustainable hydrogen sourcing for a wide variety of industries — and pushing fossil-sourced hydrogen further along the path to irrelevancy.

Image credits: City of Gold Coast and Sarah Brown via Unsplash

Tina Casey headshot

Tina writes frequently for TriplePundit and other websites, with a focus on military, government and corporate sustainability, clean tech research and emerging energy technologies. She is a former Deputy Director of Public Affairs of the New York City Department of Environmental Protection, and author of books and articles on recycling and other conservation themes.

Read more stories by Tina Casey