Desalination Outperforms Direct Seawater Electrolysis for Hydrogen Production

In a recent study published in the journal Joule, researchers from Helmholtz-Zentrum Berlin compared the costs and benefits of seawater purification and electrolysis. 

The idea initially seems good: create and develop future electrolyzers that can directly produce hydrogen from unpurified saltwater. However, a closer examination shows that years of advanced study would be necessary to develop such direct seawater electrolyzers.

Furthermore, a simple desalination process is sufficient to prepare seawater for conventional electrolyzers, negating the need for DSE electrolyzers altogether.

Fresh water is a limited resource; the oceans contain more than 96 % of the world's water. One promising solution is to feed seawater straight into a future electrolyzer to make green hydrogen using solar or wind energy.

This concept has become the subject of hundreds of millions of dollars in research funding; in 2023 alone, there were over 500 papers on direct seawater electrolysis (and the number is increasing exponentially).

No Need for New Development

However, a techno-economic examination reveals that this argument breaks down the moment the costs and benefits are examined in further detail.

There is no convincing reason to develop DSE technology because there are already efficient solutions for using seawater to produce hydrogen.

Dr. Jan Niklas Hausmann, Electrolysis Researcher and Study Lead Author, Helmholtz-Zentrum

International specialists across various fields from prestigious academic institutions, including Yale University, universities in Canada, Germany, and HZB, contributed to the commentary.

Proven Methods Work

The production of hydrogen from saltwater is already feasible. Proven processes such as reverse osmosis can be used to purify seawater for "normal," commercially available electrolyzers. From a thermodynamic perspective, the energy needed for seawater purification is merely 0.03 % of that required for its electrolysis.

The current cost also reflects this: it costs less than two cents to purify one kg of hydrogen from saltwater. However, at German filling stations, a kilogram of hydrogen costs 13.85 euros.

Investing Money Wisely

Creating novel electrolyzer types capable of continuous operation in seawater would eliminate this inexpensive purification stage. However, it is quite difficult to build DSE electrolyzers, and it is unlikely that they will ever match the efficiency and long-term stability of electrolyzers available today.

Experts perceive significant difficulties here: Numerous organic and inorganic materials found in seawater have the potential to induce fouling and corrosion, which can damage every component of the electrolyzer.

The researchers caution that while DSE is currently being marketed as a practical method for producing hydrogen, this promise cannot be fulfilled and could end up costing the government a significant amount of money.

We can compare this with the direct use of crude oil to run cars. It is possible to develop such cars, but they would just not be as efficient and long-lasting as ones running on purified petrol. This is despite the fact that the cost of purifying crude oil (via refinery) is up to 16% of the final price of the fuel, which is significantly higher than the relative cost of purifying seawater for electrolysis (<1%).

Dr. Jan Niklas Hausmann, Electrolysis Researcher and Study Lead Author, Helmholtz-Zentrum

Getting Electrolysis Research on Track to Contribute to Decarbonization

Academic research does not necessarily have to lead to immediate solutions. However, if DSE is presented as a quick fix and is pushed or hyped to the detriment of other more promising approaches, it will tie up resources that will be lacking elsewhere for the development of key decarbonization technologies. If we want to achieve net zero carbon emissions by 2050, funding must be directed to developments that can quickly contribute to this.

Dr. Prashanth Menezes, Catalysts Expert, Helmholtz-Zentrum

Journal Reference:

Hausmann, N. J., et al. (2024) Hyping direct seawater electrolysis hinders electrolyzer development. Joule. doi.org/10.1016/j.joule.2024.07.005.