[ecoled_ame]

something that tends to annoy me about hydrogen fuels - people emphasize that the combustion product is water. okay .. so that step is clean.

but how was the hydrogen in the fuel cell produced in the first place? i guess it’s an energy consuming process that produces a decent level of pollution, whether it’s by electrolysis, heating of a chemical in the presence of a catalyst, etc.

[willis936]

Electrolysis does not produce pollution. If you are suggesting a mechanism by which it does, I would love to hear it.

https://en.wikipedia.org/wiki/Electrolysis_of_water

https://en.wikipedia.org/wiki/Water_splitting

[mac01021]

The power generation mechanism you use to get the electric current for electrolysis may or may not be clean.

[willis936]

That’s entirely the point of hydrogen fuel. The process of producing or using hydrogen does not pollute. You have decoupled pollution from energy storage.

Hydrocarbons pollute by their very nature. In order to have a carbon neutral hydrocarbon cycle you need an impractical number of CO2 capture facilities.

[TeMPOraL]

And to add to your comment, spelling it out in case it isn't obvious: you can also decouple pollution from energy production using photovoltaics, wind or hydro - and suddenly most of your power chain is clean (what remains dirty is manufacturing the power generator and power storage).

[TheSpiceIsLife]

> The process of producing or using hydrogen does not pollute.

There’s no way this can be correct.

You can’t use hydrogen to produce the electricity used in hydrogen electrolysis, because that’s not permitted in this universe.[1]

Therefore the electricity has to come from some other source, which all generate life-cycle carbon emissions.[2]

1. https://en.wikipedia.org/wiki/Second_law_of_thermodynamics

2. https://en.wikipedia.org/wiki/Life-cycle_greenhouse-gas_emis...

[mac01021]

In theory you could produce the H2 off planet.

Also, that tidal power looks pretty good...

[ecoled_ame]

the electricity has to be generated somewhere. coal plants - pollution. hydropower plants - pollution. you might say hydropower plants don’t produce pollution, but it takes a lot of energy to build them and they pollute the environment with their mere existence, no more pristine nature.

[willis936]

You’re explaining how electrical power generation can cause pollution, not water electrolysis (what is being discussed).

[ecoled_ame]

yes indeed i am, because they are related. electrolysis utilizes electricity. hence the prefix electro-.

your point highlights my initial point about hydrogen fuel - ie we must look all the way up the chain and account for all polluting steps, instead of simply focusing on a single aspect.

[TheSpiceIsLife]

This is absolutely correct.

Here’s the Wikipedia entry on the subject: life-cycle greenhouse gas emissions - https://en.wikipedia.org/wiki/Life-cycle_greenhouse-gas_emis...

[namibj]

Fuel hydrogen is typically produced via steam reforming [0] and subsequent distillation/liquification.

[0]: https://en.wikipedia.org/wiki/Steam_reforming

[vbezhenar]

CH4 + H2O ⇌ CO + 3 H2

CO + H2O ⇌ CO2 + H2

For every tonne of hydrogen produced this way, 9 tonnes of CO2 is also produced.

[seventh-chord]

Isnt the ratio closer to ~6 tons of CO2 per ton of H2? You get CO2 + 4 H2, which weigh 44 and 4*2 respectively.

Also, isnt this a non-issue, because (at least in theory) the reaction is contained in your converter plant, where you can collect the CO2?

[vbezhenar]

That's quote from wikipedia. I think you're right with your calculations, so I don't really know where this number came from.

What're you going to do with that collected CO2 other than releasing it to the atmosphere?

[namibj]

Separating from other gasses, followed by sequestering.

[vbezhenar]

I guess that it would cost a lot. Technically you can do that with traditional coal plants.

[pfdietz]

The water itself is also a problem, in the stratosphere. I think this places an ultimate limit on the number of rocket launches at about 1 million Starship launches per year.