Hydrogen Production From Sea Water

Seawater, which comprises more than 95% of the Earth's water, could become a key resource in the sustainable production of clean hydrogen fuel with use of water-splitting catalysts developed by a KAUST-led team.

Water splitting could offer an appealing way to carbon neutrality, especially when coupled with renewable energy sources such as solar and wind power. Water splitting involves the breakdown of water in an electrochemical cell to produce hydrogen at the cathode while generating oxygen at the anode under applied voltage. Yet, hydrogen and oxygen evolution catalysts that perform well in fresh water become less effective in seawater because of abundant ions that can promote unwanted reactions and poison catalysts.

Highly corrosive chloride ions present in seawater undergo complex reactions that compete with oxygen evolution and generate harmful compounds, such as hypochlorite. Because hydrogen production hinges on stable and efficient reactions at both electrodes, these ions are a major challenge for seawater splitting.

Chemistexplains that hypochlorite formation can occur because it demands a lower operational voltage to meet industrial needs than the oxygen evolution reaction.

One way to tackle this issue is to design selective anode catalysts with lower voltage requirements. A nickel–iridium monolayered anode catalyst showed enhanced performance and stability in seawater thanks to synergistic effects between its metal components.

Team devised an approach that provides high-efficiency and stable hydrogen evolution electrocatalysts for seawater splitting. The researchers created tiny cubic reactors, in which the catalyst was encased in a molybdenum sulfide protective shell. The catalyst core consisted of a carbon-supported molybdenum-based redox active compound and featured a zeolite-like ordered nanoporous structure.
Using a metal organic framework-based approach, the researchers combined metal complex precursors with the linker imidazole in the presence of surfactant to generate zeolite-like zinc–molybdenum cubes. They mixed the resulting structures with thioacetamide in ethanol under reflux to form a cubic molybdenum oxide phase confined in a thin zinc sulfide shell.

Next, they chemically converted the cubic phase into the desired molybdenum sulfide-encapsulated redox active compound at high temperature before selectively etching the zinc sulfide outer layer to yield the nanoreactors.

The nanoreactors exhibited high electrocatalytic activity and stability in both fresh water and seawater. "The remarkable activity and stability are attributed to their unique structure."

The core displayed numerous active sites that boosted hydrogen production and the shell presented several defects within its layers, especially subnanometer-sized holes that allowed water molecules to permeate and access the internal active sites.

Acting as a chainmail, the shell also blocked and prevented salts from depositing on the active sites.
The hierarchical architecture of the nanoreactor isolates the electrolysis from side reactions. "Similar to a smart house, the main reaction occurs in the rooms while side reactions happen in the backyard."

Believe it or not, seawater makes an excellent base for fuel. That's because seawater contains a cocktail of elements like hydrogen, oxygen, sodium, and others, all of which are essential for life on Earth to thrive. The fuel part here comes from the hydrogen found in seawater. Unfortunately, pulling the hydrogen gas from the rest of the elements has been quite a challenge, at least until now.

The device makes what equates to seawater fuel by injecting seawater into a funnel system that drives it through a double-membrane filtration system. This system also uses electricity to successfully pull the hydrogen from the seawater, effectively separating it from the other elements found in our oceans. The results of this new study show that it could help advance new efforts to produce low-carbon fuels.

The big win here was that the system didn't create a bunch of harmful byproducts, which is something they've seen in other systems. Most of the current water-to-hydrogen systems use a single-layer membrane. However, this time the researchers brought two layers together, and it showed a better way to control the way that ions in seawater moved within the experiment, which made it more effective.

Being able to create hydrogen fuel using seawater would prove useful because it is a low-carbon fuel, which is currently used to run fuel-cell electric vehicles, and even works as a long-duration storage option for energy grids. Previous attempts to make hydrogen gas require fresh or desalinated water, and while we've seen successful water desalination systems, it's much more expensive and energy intensive.
That's because purifying the water before you use it requires expensive systems, as well as energy and even added complexity to the device, whereas a device that can use seawater to create hydrogen fuel wouldn't require those extra parts.

Producing hydrogen from seawater sounds like a dream come true!
It is abundant, free and easy.
Seawater comes as an almost limitless source of raw materials, and there's no one here to invoice it. Anyone can get a bucket full of it for free.
Industry key players are bound to fall in love with the idea.
The process of extracting hydrogen is easy. Seawater contains a large amount of dissolved hydrogen gas. It takes a simple electrolysis to extract it – we even did that as teenagers in physics class!

Here is how it works
It is natural, storable and safe
Seawater is considered a renewable energy source that could help reduce our reliance on fossil energy. And the extraction process doesn't generate carbon emissions.

Hydrogen can be stored
Stored hydrogen can be used to generate electricity or power vehicles exactly when needed.
It makes up for the intermittence of other renewables – rainy or windless days. It is perfect for regions with access to large bodies of seawater but with few conventional energy resources.
It can help reduce global warming, ensure energy security and protect the environment.

Easy-peasy, really
The process is energy-intensive: Extracting hydrogen from seawater requires a high amount of energy, and the overall efficiency is quite low.
The production is expensive: Building the infrastructure requires a very high initial investment. Maintenance is also crucial, as the salt content of seawater can cause corrosion and other technical issues.
The locations are rare: These sites need to consider water depth and quality, as well as proximity to energy sources. Not all regions are suitable for hydrogen production from seawater!
And finally, it is not as safe as you would think!

The process frees chlorine gas.
This gas combines with other natural elements and forms dioxins that pollute water, contaminate fish and transfer to humans and larger animals that eat the fish.

Do you want some examples It combines with
Water => hydrochloric acid, acute toxic effect on all forms of life.
Hydrogen => hydrogen chloride gas, highly explosive compound
Acetylene, a gas that can be produced by some marine organisms such as bacteria and certain species of algae. It combines into dichloroethane, a highly explosive compound.

Ether, trace amounts in certain species of algae. It combines into chloroacetaldehyde, a highly toxic, carcinogenic compound.
Ammonia, commonly produced by marine organisms. It combines into chloramines, a highly toxic respiratory irritant.
A promising innovation with the potential to revolutionize the clean energy sector
Hydrogen production from seawater could make a drastic difference and help address global warming in a more sustainable way.
It also has the potential to reduce our dependence on fossil fuels and move towards a cleaner and more sustainable and affordable future.
These promises make it all too easy to overlook the many challenges and risks involved.
This is my plea to the economic & energy key players: Please let's take a deep breath, sit back and think about it for a moment.

The researchers said in the press release that working with seawater would be a more economical option, as purifying water is expensive, energy-intensive, and adds complexity to devices. Furthermore, natural freshwater contains impurities that are problematic for modern technology, in addition to being a limited resource on the planet.
In addition to developing a seawater-to-hydrogen membrane system, the team noted that the study had provided a better overall understanding of how seawater ions move through membranes. This knowledge could be applied to other fields, such as producing oxygen gas.
Moreover, they said that the understanding of ion flow and conversion in the bipolar membrane system is essential for the effort to produce oxygen through electrolysis, and the team showed that the bipolar membrane could generate oxygen gas along with producing hydrogen in their experiment.
The team aims to improve the electrodes and membranes using more readily available and easily extracted materials. This enhancement in design could make scaling the electrolysis system to a size necessary for generating hydrogen for energy-intensive activities such as transportation much simpler. 

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