Hydrogen: Artificial Photosynthesis & a Clean Fuel
6 minute read
Updated on: 29 Aug 2021
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.
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.
Later, we can turn the H₂ back into electricity by using what’s called a 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:
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?
What if we could do what plants do to make energy, but do it better?