Hydrogen: Artificial Photosynthesis & a Clean Fuel

5 minute read

Updated on: 27 Dec 2020

In the last chapter, we saw that batteries allow us to replace 71% of oil-based fuels with electricity. This is for cars, trucks, and other land transport, but batteries can’t hold enough energy per kg to make airplanes or ships electric.

Hydrogen can help here and, once cheap enough, it could also be used to fuel cars! How? Hydrogen holds 128x as much energy as Li-Ion batteries per kilogram.

Image of Specific energy of Hydrogen and Li-Ion batteries

Specific energy of Hydrogen and Li-Ion batteries

In nature, hydrogen (H) usually appears as a pair of two atoms (H₂). This is also true for oxygen (O₂).

Water (H₂O) is made of hydrogen and oxygen. You’ve probably never seen water fall apart into H₂ and O₂, right? That’s because water is a stable compound. Splitting H₂O requires energy. Therefore, we can store energy by splitting water (2H₂O) into 2H₂ and O₂ and later get the energy back by bringing them back together.

Fuel from water?

The idea is simple: use clean electricity (from renewables or nuclear) to split water in a process called electrolysis.

Image of Electrolysis


Later, we can turn the H₂ back into electricity by using what’s called a hydrogen fuel cell:

Image of Hydrogen fuel cell

Hydrogen fuel cell

How is hydrogen produced today?

There has been significant demand for hydrogen since 1975.And because hydrogen today is made from natural gas, producing it causes 2% of global CO₂ emissions!

Why use gas over renewables? Cost. But with innovation and further deployment of solar and wind, we could get costs down by a lot:

Image of The price of hydrogen

The price of hydrogen

What needs to change?

Higher electrolysis efficiency: The more hydrogen per unit of energy, the better!

Higher compression efficiency: Every unit of energy we spend on compression essentially goes to waste, but we need to compress hydrogen to fit it into tanks. It’s a gas, in the end.

Higher fuel cell efficiency: The more energy we get out of each kilogram of hydrogen, the better.

Cheaper electrolysis: Energy is only a part of the cost of hydrogen. Electrolyzers need to become 20-50% cheaper to fulfill the prediction from the graph we showed before.

Infrastructure: Gases are hard to transport. To avoid the huge upfront cost of building pipelines, H₂ could be produced near to where it’s used. This is a trade off because building many smaller electrolyzers would likely be more expensive than a few big ones.

Can Artificial photosynthesis help?

Image of Photosynthesis efficiency

Photosynthesis efficiency

What if we could do what plants do to make energy, but do it better?

From an engineer’s point of view, plants are machines that turn CO₂, water and energy into sugar and oxygen.

Image of Photosynthesis equation

Photosynthesis equation

Researchers are working on artificial photosynthesis, a technology that directly turns water, sunlight, and air into H₂ and O₂, or even fuels similar to those we use in cars today!

While progress is being made, even the researchers working on this say that artificial photosynthesis won’t be an affordable technology in the near future or even in 20 years.

Price & hydrogen’s battery trap

Image of Batteries got cheaper!

Batteries got cheaper!

Aside from innovation, increased demand has enabled an economy of scale whereby things get cheaper if you make more of them.

For example, to make one bag of chips, you need to build a potato farm and a chip production factory. If you then make 100,000 more bags and divide the initial cost among them, each of them gets cheaper!

As this has already happened for batteries in cars, it might make it hard for hydrogen to catch up.


Hydrogen could replace oil-based fuels for aircraft and ships, which batteries cannot.

Making production, compression, storage, and transportation of hydrogen cheaper could have a massive impact on the whole energy ecosystem and, as a side effect, would help avoid the 2% of global emissions coming from hydrogen production today.

We need innovation!

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