Energy

Solar-powered floating rig can harvest hydrogen from seawater

Solar-powered floating rig can...
A computer render of a large-scale "floating solar rig," which captures sunlight through a photovoltaic cell and uses it to generate hydrogen through water electrolysis in the seawater it's floating on
A computer render of a large-scale "floating solar rig," which captures sunlight through a photovoltaic cell and uses it to generate hydrogen through water electrolysis in the seawater it's floating on
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A photo of the prototype device, using a container of sulfuric acid as an electrolyte instead of seawater
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A photo of the prototype device, using a container of sulfuric acid as an electrolyte instead of seawater
A computer render of a large-scale "floating solar rig," which captures sunlight through a photovoltaic cell and uses it to generate hydrogen through water electrolysis in the seawater it's floating on
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A computer render of a large-scale "floating solar rig," which captures sunlight through a photovoltaic cell and uses it to generate hydrogen through water electrolysis in the seawater it's floating on
A diagram demonstrating how the Columbia team's electrolysis system works: the red lines indicate where a catalyst is attached on one side of each electrode, and H2 bubbles that form along one surface rise into a collection chamber, while O2 bubbles vent into the air
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A diagram demonstrating how the Columbia team's electrolysis system works: the red lines indicate where a catalyst is attached on one side of each electrode, and H2 bubbles that form along one surface rise into a collection chamber, while O2 bubbles vent into the air

Hydrogen is a clean fuel source, but current methods of producing it, often by converting natural gas, can undo any environmental benefit. Producing hydrogen out of sunlight and water doesn't create any CO2, and recent research has improved the efficiency and lowered the cost of devices that achieve this. Now, engineers from Columbia University are developing a "solar fuels rig" that floats on the ocean, captures energy through a solar cell and uses it to harvest hydrogen from the water beneath it.

The rig produces hydrogen through water electrolysis, a technique where H2 and O2 gases are separated out of water by passing an electric current through the liquid. Most of the time, these devices require a membrane to separate the two electrodes, but these membranes are fragile and require very pure water, which limits their practical applications.

The device developed at Columbia can split water into hydrogen and oxygen without needing a membrane. That means it can be deployed on seawater, which would normally degrade a membrane thanks to the impurities and micro-organisms that call it home.

"Being able to safely demonstrate a device that can perform electrolysis without a membrane brings us another step closer to making seawater electrolysis possible," says Jack Davis, the first author of a paper describing the device. "These solar fuels generators are essentially artificial photosynthesis systems, doing the same thing that plants do with photosynthesis, so our device may open up all kinds of opportunities to generate clean, renewable energy."

A diagram demonstrating how the Columbia team's electrolysis system works: the red lines indicate where a catalyst is attached on one side of each electrode, and H2 bubbles that form along one surface rise into a collection chamber, while O2 bubbles vent into the air
A diagram demonstrating how the Columbia team's electrolysis system works: the red lines indicate where a catalyst is attached on one side of each electrode, and H2 bubbles that form along one surface rise into a collection chamber, while O2 bubbles vent into the air

Instead of a membrane, the Columbia system uses two mesh flow-through electrodes that are designed to be asymmetric. Each one is coated with a catalyst only on the outer edge, and the bubbles of gas form on these surfaces. H2 bubbles form on one electrode and O2 on the other, and to harvest these gases, the device uses simple physics – namely, they wait for the bubbles to grow big enough that they float up to the surface. The O2 is allowed to bubble up to the surface and escape into the air, while the H2 bubbles float into a collection chamber.

This unique electrolysis mechanism is hooked up to a photovoltaic cell, which generates the required electric current with energy gathered from sunlight. The whole shebang can be mounted on a floating platform on the open sea.

The team is currently refining the design before testing it in real seawater, and eventually scaling up the system.

"We are especially excited about the potential of solar fuels technologies because of the tremendous amount of solar energy that is available," says Daniel Esposito, lead researcher on the project. "Our challenge is to find scalable and economical technologies that convert sunlight into a useful form of energy that can also be stored for times when the sun is not shining."

The research was published in the International Journal of Hydrogen Energy and the device is demonstrated in the video below.

Source: Columbia University

Photovoltaic-powered Hydrogen Fuel Technology

8 comments
DFrancis
Seawater quite naturally comes all the way up to the coast, so why use a floating rig? Or is there too much pollution in coastal waters for the system to work?
Nik
To burn hydrogen, requires oxygen, so allowing the oxygen to escape into the air, would seem to be wasting a valuable resource. Providing pure oxygen to burn with the hydrogen would be far more efficient than using air, which is primarily nitrogen. == DFrancis, this process is vertical, so it would need relatively deep water to function effectively. It is my suspicion that a raft is cheaper to manufacture than a deep silo type construction, and also shoreline seawater contains a lot of sediments and other materials stirred up by wave action, that would be detrimental to the process.
MerlinGuy
If you can turn sunlight into electricity why would then turn it into hydrogen? That is a huge drop in efficiency. Then you would need to pressurize and tank the hydrogen - cost. Retrieve the hydrogen - cost. Store the hydrogen again - cost. And unless the second storage is its final destination, you will need to transport it again. This is a cute idea to attract investors but the unavoidable costs suck up all the profits so I'm out.
ei3io
@Merlinguy,, wider vision shows that H is the cleanest solar infinitely sustainable non polluting fuel on the planet. Air travel which truly benefits from the lightest weight fuel system is better than batteries and it will ultimately use H fuel cells for longest distance travel ability. To transport H you can have an ocean floor resting pipe system transporting it to shore fuel stations. With wind and solar PV near any water sources H will easily and very cheaply fuel the future. Their next gen cad model would consider massive waves in storms with ability to survive which deep water systems can easily do as long as the surface modules survive or are easily replaced say from a very rare rouge wave.
Supervolant
It seems no-one in this comment section knows how huge this is. I am here to tell you guys. THIS IS BIG NEWS! Very Good University of Columbia!
Tom Lee Mullins
I think that will make getting hydrogen for fuel cells a little greener.
BanisterJH
@DFrancis: Coastal real estate is somewhat more expensive than is offshore real estate. Also, boats have fewer regulations with which they must be careful to comply if they stay farther from where people live. What I have to wonder, though is the business plan for building it. A fueling station for the E/S Orcelle? Or, will they build their own boats simultaneously?
Douglas Bennett Rogers
The photovoltaics have about the same reflectivity as water. The water cools them. They can partially replace plankton with little impact. They might drop right in to the Sargasso Sea eco system and be relatively safe from storms.