As renewable electricity costs continue to fall, green hydrogen (H2) production via water electrolysis is gaining pace as a means to decarbonize worldwide energy systems. Due to the necessity of ultrapure fresh water for electrolysis and the extensive availability of salt water, significant research efforts have been dedicated to developing direct salt water electrolysis technologies for mass production of green H2. This article will look at the possibility of producing green hydrogen from salt water, a challenging move that could help accelerate sustainability.
Image Credit: Feelindesign/Shutterstock.com
Green Hydrogen and its Impact on Fresh Water Sources
Green hydrogen is a sustainable energy carrier, which can be produced directly by water electrolysis, potentially substituting fossil fuels to attain carbon neutrality. Renewable energy is used to produce hydrogen from water. Hence its production is free from greenhouse gases and carbon capture technology.
The energy stored in 1 kg of green hydrogen is almost 2.5 times more than in natural gas. Since the 19th century, this gas has been employed in vehicles, airships, and spacecraft fuel cells.
In the near future, green hydrogen will replace fossil fuels to provide energy for almost everything, from cars to buildings. However, producing global hydrogen could strain freshwater sources for drinking and use in numerous industrial processes.
Due to its large reserves, the electrolysis of salt water to produce green H2 by renewable electricity is now considered a promising contender for sustainable energy.
Corrosion of Electrodes
Effective water separation relies on catalytic electrodes, necessitating pure water under fundamental conditions to prevent deterioration. Ocean water contains organics and dissolved salts such as sodium chloride that shorten the system's useful life by corroding typical catalysts.
Industrial manufacturing of green hydrogen fuel via salt water electrolysis has been hampered by expensive desalination and purifying technologies to provide significant quantities of clean deionized water for efficient electrolysis.
Efforts to Make Salt Water Green Hydrogen Production Viable
Coating of electrodes
Stanford researcher Hongjie Dai and his team aimed to find a technique to keep ocean water from corroding the submerged anodes due to its high salt content. They discovered coating the anode with rich layers of negative charges reduces the breakdown of the underlying metal.
They employed iron, nickel hydroxide, and nickel sulfide to create a negatively charged coating that protects the anode during electrolysis. As a result, they could generate ten times more electricity through the multilayer device, accelerating hydrogen production from salt water.
Salt water electrolysis with a semi-permeable membrane
Researchers led by Evan Pugh and Bruce Logan have succeeded in splitting seawater to produce green hydrogen.
The pre-desalination procedure in this process is costly. However, the team has reduced the cost by employing a thin semi-permeable membrane to filter water in the reverse osmosis treatment.
The reverse osmosis membrane replaced the typical ion exchange membrane seen in electrolyzers. Reverse osmosis works by applying a lot of pressure to the water and forcing it through the membrane while leaving the chloride ions behind.
Platinum catalyst to prevent recombination of ions
A novel catalyst has been created by scientists from Shaanxi Normal University and Swinburne University's Centre for Translational Atomaterials that can synthesize green hydrogen from seawater via solar energy.
The researchers designed the Ocean-H2-Rig prototype to use this new catalyst. It can manufacture green hydrogen from salt water floating on the water's surface.
In typical photocatalysts, water splits into hydrogen and oxygen when electrons and holes are separated in response to solar light. The separated electrons and holes tend to unite again, drastically lowering the photocatalytic activity and the efficiency of hydrogen synthesis.
The photo-generated electrons are successfully extracted by the single-atom platinum catalyst created in this work, preventing undesired recombination. It significantly boosts the effectiveness of hydrogen production.
The reusable catalyst is among the most efficient ever reported since it promotes highly efficient hydrogen generation with an exceptional quantum yield of 22.2% under LED-550 illumination.
Salt water electrolysis via forward osmosis
Harvard researchers successfully used forward osmosis to separate salt water into clean hydrogen and oxygen gas. They created hydrogen gas by forward-osmosis and electrochemical water splitting, which is useful for storing renewable energy.
The researchers enhanced the natural mechanism of osmosis to collect clean water from natural sources such as the ocean. There is no requirement for a separate water purifying system because this technology enables salt water use.
End-Of-Life Platforms Offer Opportunities
The continuous rapid expansion of offshore wind power generation combined with the end-of-life oil and gas infrastructure provides prospects for offshore green hydrogen projects.
Existing gas infrastructure can generate large amounts of green hydrogen on offshore locations using renewable electricity from offshore solar and wind farms. This will reduce transportation and production costs and prevent huge expenditures on electrical networks because transporting gases is less expensive than electricity.
Future of Salt Water Green Hydrogen Production
Seawater is a naturally abundant resource; therefore, producing green hydrogen from it via electrolysis can help to some extent with the world's current energy crisis. However, corrosion of electrodes from salt waters hampers the mass production of green hydrogen.
Therefore, there is a critical need for strong and effective electrocatalyst technology that can avoid or withstand chloride corrosion and precipitate formation on the electrodes. Considerable attempts have been made in seawater electrolysis, although long-term stability and selectivity have not yet been accomplished.
Continue reading: Can Green Hydrogen Replace Natural Gas?
References and Further Reading
Ibrahim, O. S., Singlitico, A., Proskovics, R., McDonagh, S., Desmond, C., & Murphy, J. D. (2022). Dedicated large-scale floating offshore wind to hydrogen: Assessing design variables in proposed typologies. Renewable and Sustainable Energy Reviews, 160, 112310. https://doi.org/10.1016/j.rser.2022.112310
Matich, B. (2021). Novel Catalyst Produces Green Hydrogen from Seawater via Solar. [Online]. PV-Magzine. Available at: https://www.pv-magazine.com/2021/02/04/novel-catalyst-produces-green-hydrogen-from-seawater-via-solar/ (Accessed on 22 July 2022).
Penn State. (2020). Generating Renewable Hydrogen Fuel From The Sea: Researchers Use Membranes That Remove Salt From Water To Help 'Split' Sea Water Into Fuel. [Online]. ScienceDaily. Available at: www.sciencedaily.com/releases/2020/09/200929173419.htm (Accessed on 22 July 2022).
Stanford University. (2019). Researchers Create Hydrogen Fuel from Seawater. [Online]. ScienceDaily. Available at: www.sciencedaily.com/releases/2019/03/190318151726.htm (Accessed on 22 July 2022).
Tashie-Lewis, B. C., & Nnabuife, S. G. (2021). Hydrogen production, distribution, storage and power conversion in a hydrogen economy-a technology review. Chemical Engineering Journal Advances, 8, 100172. https://doi.org/10.1016/j.ceja.2021.100172
Veroneau, S. S., & Nocera, D. G. (2021). Continuous electrochemical water splitting from natural water sources via forward osmosis. Proceedings of the National Academy of Sciences, 118(9), e2024855118. https://doi.org/10.1073/pnas.2024855118