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Comment by mikeash | Hacker News Reader

“When it's fully loaded, the fuel contains about three percent hydrogen and 97 percent supporting material.”

This fuel, which is 97% inert material, is supposed to have energy density comparable to gasoline? Either I’m fundamentally misunderstanding something or this is buulllllshiiiit.

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The Toyota Mirai can store 5kg of hydrogen (giving it a 500km range). This system would require about 150kg of inert material to store the same amount of hydrogen. That's only about three times the weight of a full tank of gas and doesn't seem totally impractical. The other claims sound pretty far-fetched though. For twice the range of an ICE car, it would need a much larger tank.

1. https://insideevs.com/toyota-mirai-fuel-cell-sedan-priced-at...

It seems reasonable to assume this stuff has a density similar to water, since it’s mostly water anyway. That means you’d need a 150 liter tank to achieve 500km of range. A typical car has, what, a 40 liter tank? And they’re promising more like 1,200km of range from that size tank.

60% water, so it depends on what the other 37% is

Even if the other 37% takes up no space at all, it still doesn’t come close to adding up.

I think it's probably the latter. Unless they are doing fusion or something, there's no way they're getting that kind of density.

Yeah I don't see how it works. Google tells me hydrogen's got ~3x the energy density of gasoline. That's quite a numbers gap.

You can make a lot of that back with the difference in efficiency between an internal combustion engine (theoretical max of 50%, and only under ideal conditions) vs the efficiency of an electric motor (90% or better) and associated losses from the motor controller and the fuel cell.

This fuel is 3% hydrogen and is claimed to achieve 200% the MPG of gasoline.

Hydrogen has 3x the energy so that gets us to 9%.

Let's say hydrogen has 4x the efficiency of turning energy into miles (which I think is a reasonable estimate), so that gets us to 36%.

This stuff may be denser than gasoline. It's 60% water. Let's make the extremely generous assumption that the rest of the stuff occupies no space at all, giving a density of 1.7kg/L. Gasoline is 0.7kg/L, so that's an improvement of 2.4x which gets us to 86%. Still more than a factor of 2 short of the claim.

Maybe they're measuring by weight instead of moles?

They’re measuring by volume, saying a standard size fuel tank would give twice the range with this stuff.

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