With fusion in the news often, I was wondering what makes it special as opposed to simply burning hydrogen with oxygen like a fuel cell does?
Doesn’t both require the uneconomical electrolysis to source the hydrogen in the first place?
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Fusion produces significantly more energy than fire. According to [this](https://www.energy.gov/science/doe-explainsdeuterium-tritium-fusion-reactor-fuel), the hydrogen in a gallon of seawater is enough to produce as much energy through fusion as burning 300 gallons of gasoline.
“Burning” hydrogen is just a chemical reaction. It produces some energy, yes.
Hydrogen fusion is a nuclear reaction where only hydrogen is fused together to produce quite a bit more energy.
Hydrogen is typically sourced from steam cracking of methane or electric decomposition of water.
Just *burning* hydrogen reacts it with oxygen gas to turn it back into water, releasing the same amount of energy originally required to separate the water.
Fusion is a completely different process, putting the hydrogen atoms under so much heat and pressure that a nuclear reaction occurs. Two hydrogen nuclei are converted into neutrons in the reaction, releasing energetic photons and positrons that annihilate an electron, converting their mass directly into energy.
This is a proportionally massive release of energy compared to the chemical burning process, but it’s incredibly difficult to start and sustain – you need more heat and pressure than the core of the sun to make it happen.
burning hydrogen is a chemical reaction where you cause a minor change to the atoms “soft outer shell” to get a (comparably) small amount of energy.
fusion is a physical process where the “hard core” of the atom changes (by literally FUSING two such cores together) which gives you (comparably) insane amounts of energy.
it’s literally the difference between a campfire and a nuke in terms of power.
but fusion uses the heavy isotopes (=versions) of hydrogen, one of those you can get from sea water, basically by filtering and then yes, using electrolysis or similar processes. but again the energy invested here is orders of magnitude lower than what you can get from the fusion process.
The fuel for fusion reactors is actually harder to get ahold of than for fuel cells because it requires special types of hydrogen and helium. What makes fusion so desirable is that nuclear reactions release far more energy than chemical ones. All that energy is more than enough to make up for the extra cost of fuel.
Burning a big tank’s worth of hydrogen lets you drive around for a good while in a car.
Fusing a big tank’s worth of hydrogen is [this](https://youtu.be/Q3ezhvCzWCM?t=23) amount of energy.
Burning hydrogen with oxygen basically just reverses the electrolysis you did to produce the hydrogen. One splits water into hydrogen and oxygen, and the other puts them back together again. Even if all of the steps were 100% efficient (i.e. no energy losses), by burning hydrogen at most you’d recover the energy you had to put in to do the electrolysis, and so you’d be back where you started from.
However, *fusing* hydrogen is a different beast altogether. You see, if you fuse hydrogen atoms into a helium atom, the resulting helium atom is actually a bit lower in mass than the sum of the masses of the hydrogens that went in. The difference in mass is released as energy, according to Einstein’s famous formula E=mc^(2), where c is the speed of light in m/s, i.e. (approximately) 300,000,000, and thus c^(2)=90,000,000,000,000,000. In other words, if you convert just 1 gram of mass to energy, you’ll get 90 **trillion** Joules of energy, i.e. enough to power New York City for 2 whole **years**. In hydrogen fusion, about 0.71% of the original hydrogen mass is converted into energy, so 1 kg of hydrogen in results in about **half a trillion** Joules of energy out. For comparison, when you burn 1 kg of hydrogen, this releases only about 100 million Joules of energy, i.e. about 5,000 times less energy.
So yeah, electrolysis requires energy, and if you just burned the hydrogen again, you’d *at best* get that same energy back. But fusion allows you to unlock a far greater source of energy that is totally worth the little bit of energy required for the electrolysis.
Buring hydrogen means we need to get hydrogen. Mostly from methane or water. To do this we use electricity to break the hydrogen free and collect it. If we then burn it, we get water as the result. So if our source of hydrogen is water, it takes just as much energy to make the hydrogen as we get out of it by burning it.
If we fuse the hydrogen together, we get helium, and that reaction releases a lot more energy than burning hydrogen, so we end up with a net gain of energy.
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