Hybrid Reactor Uses Bacteria to Turn CO2 into Useful Molecules on Mars or Earth

The semiconductor nanowires take in the solar energy and pass it on to the bugs who do the chemistry for us.
Derya Ozdemir

Thinking about colonizing Mars is one thing; however, actually sustaining thousands of lives up there is completely something else. We can’t ship Amazon packages between Mars and Earth back on forth: one, that would be extremely expensive; two, it is not sustainable. So, we need to get smart. 

Brilliant ideas take brilliant minds, and a team of chemists from the University of California, Berkeley and the Lawrence Berkeley National Laboratory seem to have a brilliant solution to this decades-old problem.

These researchers have been working on a hybrid system that creates the building blocks for organic molecules by capturing the energy of sunlight. And this system works by combining bacteria and nanowires. Their device might be a very important step for a possible future on Mars.


What are nanowires?

Nanowires are incredibly thin silicon wires that are about a hundredth of the width of a human hair. We use them as electronic components, sensors, and solar cells.

According to the project leader Peidong Yang, “On Mars, 96% of the atmosphere is CO2. Basically, all you need is these silicon semiconductor nanowires to take in the solar energy and pass it on to these bugs to do the chemistry for you. For a deep space mission, you care about the payload weight, and biological systems have the advantage that they self-reproduce. You don’t need to send a lot. That’s why our biohybrid version is highly attractive.”

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In order to work it, you only need sunlight and water, which Mars has plenty on its vast surfaces in frozen form.

How does the system work? 

The system works like photosynthesis.

The left side of the reactor is the chamber which contains the nanowire-bacteria hybrid that reduces COto form acetate. Oxygen is produced on the right side.

Hybrid Reactor Uses Bacteria to Turn CO2 into Useful Molecules on Mars or Earth
Source: UC Berkeley/Peidong Yang

The team first demonstrated the nanowire-bacteria hybrid reactor five years ago; however, the solar conversion efficiency was only about 0.4%. The researchers tried to increase the efficiency by putting more bacteria onto the nanowires, however, that idea wouldn't make the cut.

The efficiency of the system is comparable to the plant that best converts COto sugar, which is sugar cane by 4-5% efficiency.

Hybrid Reactor Uses Bacteria to Turn CO2 into Useful Molecules on Mars or Earth
Source: UC Berkeley/Peidong Yang

Here, you see the reactor at its top efficiency. They achieved this by operating the optimal acidity for bacteria, which gave more efficient conversion of solar energy to carbon bonds. The researchers were able to operate the reactor for a week. 

It should be noted that the nanowires were used only as conductive wires, not as solar absorbers. Yang said, “These silicon nanowires are essentially like an antenna: They capture the solar photon just like a solar panel. Within these silicon nanowires, they will generate electrons and feed them to these bacteria. Then the bacteria absorb CO2, do the chemistry, and spit out acetate.”

As photosynthesis goes, the carbon dioxide molecules and water turn into acetate and oxygen. The oxygen might be of use to Mars colonists of the future by adding to their artificial atmosphere. 

The system could be beneficial for both Mars and Earth 

Yang is also working on potentially providing food for the Martians by efficiently producing sugars and carbohydrates from sunlight and CO2.

Moreover, the biohybrid can pull carbon dioxide from the air on Earth to make organic compounds. You can almost think of this as planting new trees. While producing energy, it helps with climate change too. It brings a good deal for everyone involved. 

The study was published in the journal Joule.

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