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Comment by ajnin | Hacker News Reader

> "Hydrogen is the ultimate clean energy."

This is a lie pushed by oil companies. First it is incorrect because hydrogen is not a natural energy source, it is a way to store energy. But above all, currently the vast majority of hydrogen is made by steam cracking methane or other hydrocarbons, which is a process that releases CO2. You can think of hydrogen production + hydrogen use as a combustion with additional steps. And since the hydrogen supply chain is very inefficient (hydrogen is very light so you need to compress it a lot to store it, it is a very small molecule so it leaks very easily, and when you use it you need to decompress it so you get more losses due to thermodynamic effects) it turns out as quite bad from the point of view of CO2 emissions. It is just a way to sell more oil.

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> First it is incorrect because hydrogen is not a natural energy source, it is a way to store energy.

Yes, unless you count fusion. But that's a completely different context.

Still not a natural energy source, fusion as envisioned requires D+T fusion, not extracted from hydrogen gas but from seawater and lithium irradiation. Hydrogen gas is not naturally occurring on Earth, so by definition it cannot be a "natural" energy source. It's an intermediate product.

> Still not a natural energy source, fusion as envisioned requires D+T fusion, not extracted from hydrogen gas but from seawater and lithium irradiation.

You can fuse hydrogen, too. It's 'just' harder.

> Hydrogen gas is not naturally occurring on Earth, so by definition it cannot be a "natural" energy source. It's an intermediate product.

Not quite sure anything would count as 'natural' in that sense. Almost everything is processed in some way. I thought the problem was with 'energy source', not with 'natural'.

Steam methane reforming is a process that produces hydrogen and CO2, as you say. But we can just pump that CO2 back where the methane came from (or older depleted gas fields).

Since that storage was secure enough to contain the methane for a hundred million years, it can hold the CO2 just fine as well.

Are we sure about that ? I must admit I'm not a geologist, but CO2 has a different chemistry as methane, it becomes acid when dissolved in water, how would rocks behave when exposed to acid for thousands of years ? Are the rocks still gas-tight when they have been emptied, which causes movement and potential fractures, or when fracking was used for extraction ? How does it work to pump back CO2 in the same field you extract methane from ? Do we even have enough room to store the massive volumes of CO2 were generating ? An accidental release of such a store of CO2 would be a disaster of enormous proportions.

> how would rocks behave when exposed to acid for thousands of years

Rocks react quite well. Most are stable, some others absorb the gas and become stable.

It's water that doesn't deal well with it. It carries the CO2 into any place that it goes. What concerns me is that it's common to extract methane from places where it's trapped between a solid rock and a porous one full of water. That does not look like a proper place to inject CO2, but it's the place that every article about CO2 entrapment talks about.

There has been so much research into caprock permeability/stability, we know that shit. People have produced several atlases full of possible CO2 sequestration reservoirs with different geological properties, injectivity and maturity based on 3D seismics and core sample drillings etc.

CO2 sequestration is ready to go. Just like CO2 capture is ready to go. You have several actors commissioning projects now in Europe with 20-40 megatonnes stored per year.

That's good to know.

AFAIK, that research did not make into the mainstream news. But then, geological research never does.

You seem to have read only the introductory paragraphs.

There is little need to store or transport hydrogen that may be produced right where and when it is needed.

If I read the abstract correct it's doing electrolysis of moisture in the air. That's a process that inherently uses more energy then you get back out of the hydrogen. After all burning hydrogen just turns it back into water, and we can't have more than 100% round-trip efficiency.

I could imagine it as a viable storage technology, e.g. if you want to install a solar farm in a remote location you could have it produce hydrogen from the air and sell that.

Obviously all conversions involve losses. If you have electric power but need hydrogen, you have to make the hydrogen, whatever the loss. This method has lower loss than others.

Probably ammonia will be a better transport medium than hydrogen, but you need hydrogen to make ammonia.

Regardless of energy transport, we will be making huge amounts of ammonia using green hydrogen in the future.

We need ammonia for fertilizer, and right now we get the hydrogen for that from methane, which can't be the plan long-term. At the moment switching to hydrolysis would double to quadruple the cost of the hydrogen, but eventually falling electricity and rising natural gas prices should invert that. The Haber-Bosch process itself doesn't require petrochemicals, it's just the cheapest way to run it in the current market.

"electrolysis". Hydrolysis is a wholly different activity.

The intent of the method presented is to make electrolysis energetically cheaper. It might end up financially cheaper, depending on what the apparatus costs, which will of course start out high and come down if used much.

Apparently there are practical catalytic processes to go directly from N2 and H2O to NH3 and O2. Everything will compete, and a few processes will win. Tolerance of impurities in the water has often been a problem. Where you have to distill the water first, that increases cost.

And what would be the use of producing hydrogen when and where it is needed? What's the point of the hydrogen? This might be useful when there's a need to use hydrogen for some chemistry, but for energy purposes, if you don't need to store any energy and you'd be ready to use the energy then and there, what's the point of generating hydrogen?

Last year the world used seven hundred million tons of hydrogen, almost all produced from natural gas.

In the future the world will use many, many times more, on top of all current uses producing steel, ammonia, and even methane, liquifying for aviation, and pushing underground to produce power from later.

The authors have no crystal ball. But need for lots of hydrogen is an easy call, and motivates better ways to produce it. Once produced, it will be used according to the needs of those producing it. The authors' speculations on such use do not bear on the value of the work.

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