H2 may well be a more potent GHG when compared to CO2, but it's tendency to remain in the atmosphere for a long time is a factor than shouldn't be ignored and doesn't seem to be mentioned by your first citation. I.e. H2 may be 16x more potent than CO2 but if it reacts away within hours/days/[<16th of the time that CO2 stays around] then its overall contribution to warming will be less than CO2. (I don't know what this figure is, but I believe Hydrogen is pretty reactive so doesn't tend to stick around that long)

From your second citation:

> The evidence base relating to non-GHG emissions from end-use in heating applications is almost non-existent

It then says that a single study:

> suggests there is potential for up to six times higher point NOx emissions compared with natural gas".

and that it could be significantly reduced with catalytic converters.

The points you raise are not nearly as unequivocal as you make them out to be. I also don't feel like Hydrogen is going to solve all of our problems - it has many problems that needs to be overcome. But it could well play a role in certain areas when it comes to getting off fossil fuels, so studies into more efficient production of it will surely be valuable.

>H2 may well be a more potent GHG when compared to CO2, but it's tendency to remain in the atmosphere for a long time is a factor than shouldn't be ignored and doesn't seem to be mentioned by your first citation. I.e. H2 may be 16x more potent than CO2 but if it reacts away within hours/days/[<16th of the time that CO2 stays around] then its overall contribution to warming will be less than CO2. (I don't know what this figure is, but I believe Hydrogen is pretty reactive so doesn't tend to stick around that long)

Usually these numbers take that in consideration and the two are compared over a certain number of years, i.e. 100 years. A quick Google seems to confirm this, H2 is ~10 more potent than CO2 over 100 years.

Good point

Still.. we're talking about unintentional leaks here. With the alternatives, CO2-emissions is an unavoidable by-product (in theory it can be managed with CCS, but not for transportation)

We should use batteries whenever we can, but seems to me like hydrogen is an essential component of a green, fully carbon neutral economy.

Though I agree with the comment above that it's a bit... misleading.. to call hydrogen the ultimate clean energy. Green hydrogen (do differentiate from hydrogen made from natural gas) is a very good clean energy carrier. That'd be more precise to say.

It's GWP over 100 years. This is stated in the source: "We estimate the hydrogen GWP(100) [ie, over a 100-year period] to be 11 ± 5; a value more than 100% larger than previously published calculations." In the past, I've seen ranges between 4.3 and 5.8 for the GWP over 100 years for hydrogen mentioned in articles.

There are numerous studies on the NOx levels produced by combusting hydrogen in air and they all show levels much higher than those associated with methane (and methane NOx emissions are already recognised to be be health threatening in urban environments) because hydrogen burns at a higher temperature which promotes the formation of nitrogen oxides.

All that may be true, and I'm not disputing any of it. But all energy sources and storage methods have their drawbacks. They're not necessarily a reason to something out. I'm sure Hydrogen will play a role in certain areas (e.g aviation and steel production). The tech is still young so there's bound to be significant developments coming.

> "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.

> 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.

Green Hydrogen is going to be big. You are correct that if you are burning it then you have taken a wrong turn, or at least haven't got to the final destination.

Mostly it will be a sink of energy and a chemical feedstock. That is still massive, size of the oil industry scale big.

The prioritization that you propose will make the oceans saltier. Whereas, burning H2 is water-neutral.

For fixed infrastructure, nothing beats power lines. For mobile applications, hydrogen has numerous problems. There are other options, like batteries, ammonia, synthetic hydrocarbons etc that should be explored further.

Hydrogen doesn't even come close to deserving the title "the ultimate clean energy".

That wholly misses the point.

We need hydrogen production in unlimited amounts for myriad processes. Want synthetic ammonia? Need hydrogen. Methane? Hydrogen. Kerosene? Hydrogen. Green steel production? Hydrogen.

Furthermore, liquified hydrogen is the future of aviation.

So a tech that produces hydrogen efficiently anywhere there is air is intrinsically important.

> Furthermore, liquified hydrogen is the future of aviation.

What makes you think so? Why not eg methane? Or other synthetic carbohydrates?

Performance-wise there's nothing close. You fly twice as high because hydrogen burns so lean, and you only need roughly 1/5th the equivalent mass of kerosene in fuel to get you the same distance. There are obvious barriers in the way (cost, certification, handling), but the potential benefits have been known for a long time.

The main problem with LH2 is that it won't fit in the wing tanks like kerosene. The tanks may be very light, because the pressure is low and the LH2 weighs nothing, but they will be big!

Some bet LH2 aircraft will have a wholly new shape, more like a lifting body, with a lot more inboard room for the bigger tankage. But another possibility is long underwing nacelles, alongside the engines. Those might even be retrofitted to existing airframes.

Some people dislike the idea of sharing the cabin with inboard hydrogen tankage, as a safety concern. Fuel tanks shearing off with the wings in a crash has saved lives. Probably the nacelles would be rigged to be dropped in an emergency, to leave behind detonation risk.

Yeah that's right, you need roughly twice the fuel volume, though that's easier to accommodate than needing to deal with a heavier fuel like ammonia, for example.

Blended wing bodies and flying wings might make more sense with LH2. They haven't happened so far because they're harder to certify (essentially from scratch vs a standard design which uses evidence from previous designs to expedite certification), and they don't work too well with existing airport infrastructure. If you're going through the trouble of certifying LH2 anyway, that could provide justification for a new design, and working with airports to get the infrastructure going.

I am betting compatibility with past practice wins over incremental efficiency.

But I have no way to evaluate whether retrofitting existing airframes with underslung tankage will be practical.

I tend to agree. Performance-wise, kerosene is "good enough". The only area where I see LH2 being worth the effort is military aircraft, especially unmanned.

Of course, that's not a knock against green hydrogen itself (which I'm sure some will interpret it as) since kerosene is really just hydrogen with extra steps. But there are more factors that go into an effective propulsion system than just raw performance and efficiency.

> Performance-wise, kerosene is "good enough". The only area where I see LH2 being worth the effort is military aircraft, especially unmanned.

I'm not so sure. The military tends to put a premium on not exploding, even when fired up on. Even at the expense of efficiency.

Case in point: TNT vs dynamite.

> TNT has never been popular or widespread in civilian earthmoving, as it is considerably more expensive and less powerful by weight than dynamite,[12] as well as being slower to mix and pack into cylindrical boreholes; for its part, dynamite has never been popular in warfare because it degenerates quickly under severe conditions and can be detonated by either fire or a wayward bullet. TNT's primary asset is its remarkable insensitivity and stability: it is waterproof and incapable of detonating without the extreme shock and heat provided by a blasting cap (or a sympathetic detonation); this conveniently also allows it to be melted at 81 °C (178 °F), poured into high explosive shells and allowed to re-solidify with no extra danger or change in the TNT's characteristics.[13] Accordingly, more than 90% of the TNT produced in America was always for the military market, with most filling shells, hand grenades and aerial bombs and the remainder being packaged in brown "bricks" (not red cylinders) for use as demolition charges by combat engineers.

From https://en.wikipedia.org/wiki/Dynamite

See also https://en.wikipedia.org/wiki/Multifuel#Underperformance_iss... and https://en.wikipedia.org/wiki/JP-8 (they add special stuff to make military fuel auto-ignite at a higher temperature than civilian fuel).

However, you might be right that in unmanned situation the military might be ok with more dangerous LH2. Though I doubt it, because the LH2 storage tanks on the ground also need to be relatively close to the front lines. And unless you make it on-site, you need to have a logistics train to get the LH2 there.

LH2's extreme mass-energy density will make other aircraft unable to compete, because the weight savings may be sold as additional paying cargo capacity.

That presumes a joule of LH2 is the same price as of kerosene. But LH2 may end up much cheaper, increasing the gap.

One would suppose mass energy density is even more important for rockets.

In practice, only some rockets use LH2. Many rockets use souped up kerosene (RP1) or, more recently, methane.

Compare https://en.wikipedia.org/wiki/Liquid_rocket_propellant#Hydro... and https://en.wikipedia.org/wiki/Hydrogen-powered_aircraft

Also:

> With materials available in the 2020s, the mass of tanks strong enough to withstand this kind of high pressure will greatly outweigh the hydrogen fuel itself, largely negating the weight to energy advantage of hydrogen fuel over hydrocarbon fuels. Hydrogen has a severe volumetric disadvantage relative to hydrocarbon fuels, but future blended wing body aircraft designs might be able to accommodate this extra volume without greatly expanding the wetted area.

From https://en.wikipedia.org/wiki/Aviation_fuel

The quote concerning mass of tanks is talking about compressed hydrogen storage, which people don't really consider feasible for large aircraft. Cryogenic liquid hydrogen storage is the way.

The need for higher mass density exhaust to provide enough absolute thrust to get off the ground overwhelms H2's energetic efficiency. Thus, SLS, like STS before it, depends on solid-fuel rockets until well clear of the pad, and then jettisons them.

Aircraft operation involves nothing analogous.

Hydrogen is pretty neat as a storage medium. It's easier to store a few terawatthours in gas than in batteries.

Most of all it's an intermediate for even neater chemical storage mediums. The entire range of non-biological regenerative fuels (or non-biological, period, if we include fossils in the biological group), including reduced Fe dust cycles, ammonia or plain old "e-fuel" hydrocarbons, they all start with hydrogen as the first stage. It's the natural short term storage medium that will be used as an input buffer for downstream processes so that they don't have to follow supply peaks as closely as they would have to without that buffer.

Ammonia and synthetic hydrocarbons will be built from green hydrogen though.

> Hydrogen leaked into the atmosphere is 6-16 times more potent than CO2 as a greenhouse gas

Which is a problem considering how small the H2 molecule is: we can't reuse our existing LNG pipelines.

Personally, I believe aerochemistry will "work out" in the long term by generating short to medium length aliphatic compounds from CO2 and H2O: we'll eventually figure out the catalyzation from sunlight.

We can then have access to lots of energy, with a negative carbon balance, using always sunny surfaces like the Sahara desert - which sits conveniently close to Europe!

This could help with the European energy problems if only France would stop thinking short term and try to protect and extend the commercial life of its ailing nuclear energy business (50% of which is currently closed down to being unsafe/uncoolable etc) by shooting down initiatives to build LNG pipelines from North Africa to Europe.

Yes, they are doing that, even now that they (and Germany, and the rest of Europe...) are facing a winter without Russian gas: https://www.archyde.com/gas-spain-criticizes-frances-opposit...

Unfortunately, France stands in the way between the shortest route from North Africa to continental Europe through Gibraltar.

If a pipeline can't be build from Spain to Germany by going through France, the next best would be from Italy.

"Which is a problem considering how small the H2 molecule is: we can't reuse our existing LNG pipelines."

Assuming you mean natural gas pipelines, this isn't the case everywhere. Many flexible seals and ancillary equipment will need to be replaced but most low yield strength pipelines like the ones commonly used in Europe are easily adapted to H2 use. The American network use more high yield strength steel which is less suitable to hydrogen service.

It is vastly more cost effective to build electric transmission lines instead of gas pipelines, and crack hydrogen at the point of use.

Furthermore, the desert is a lousy place to put solar panels. They get hot and dusty, making them inefficient and shortening their life. The best places are floating on water, and sharing pasture and crop land. Spain, Italy, and Greece have plenty of room for such solar. Portugal, too, and former Yugoslavia, Albania and Bulgaria.

Nukes will shortly be unable to produce competitive power, and will be mothballed except where taxpayers are forced to subsidize them.

> It is vastly more cost effective to build electric transmission lines instead of gas pipelines, and crack hydrogen at the point of use

No it's not.

You are building in your assumption that I talk about solar panels for electricity generation. I don't.

I'm talking about direct aerochemistry, without separate solar panels, to avoid tackling up the conversion rate of solar to electricty on top of the conversion rate of the chemical reaction that would create the hydrocarbons.

There is gas in North Africa. This gas can be directly burnt to generate heat. It can also be used to generate electricity. That's short term.

In the long term, we'll be able to make similar compounds from energy (sunlight or heat) + CO2 + H2O.

Inbetween, there's a window of opportunity for nuclear and solar, but both are extremely polluting due to the metals used: we should avoid getting locked in this bad situation.

Also, I think the lack of nuclear accident in Western Europe so far has just been luck. With the dense population, it's a catastrophe waiting to happen.

> Furthermore, the desert is a lousy place to put solar panels

I don't think you understand, as I don't suggest at all the use of solar panels.

Using solar panels to generate energy is nice, but it's at best carbon neutral. I'm talking about the future: being carbon negative: extracting CO2 from the atmosphere and generating a usable from of energy.

If you are not talking about solar panels, you are not in the conversation. Photovoltaic solar is vastly cheaper than any known photochemical process. It is strongly carbon-negative. The metals involved do not make it a polluter.

It is possible that a direct photochemical process cheaper than photovoltaics + electrolysis will be discovered, but none is known today, and photovoltaics cost is still in free fall, a moving target.

> If you are not talking about solar panels, you are not in the conversation.

(!!!)

You are locked in the present, and existing sources of energy that are polluting yet labelled as "green". Think about the future instead!

> Photovoltaic solar is vastly cheaper than any known photochemical process.

Emphasis on KNOWN. There's lot of research going on.

> It is strongly carbon-negative.

Unless a process removes CO2 from the atmosphere, a process is not carbon negative.

You may say that it reduces the interest in other methods that generate CO2, and therefore, by extension, it's like removing CO2, but it's not the same.

> The metals involved do not make it a polluter.

https://www.cfact.org/2019/09/15/the-solar-panel-toxic-waste...

"Solar panels generate 300 times more toxic waste per unit of energy than nuclear power plants. They also contain lead, cadmium, and other toxic (even carcinogenic) chemicals that cannot be removed without breaking apart the entire panel. Worse, rainwater can wash many of these toxics out of the fragments of solar modules over time"

I think you are blind to the various negatives of solar power.

> It is possible that a direct photochemical process cheaper than photovoltaics + electrolysis will be discovered,

Exactly my point. Thanks for at least agreeing in the end.

Efficient photochemical lysis is *possible", but not the way to bet. If it happens, it will enter the mix. There is no reason to think it would involve less use of metals than photovoltaics.

Until hydrocarbon burning is a negligible part of energy production, a kWh of solar exactly displaces the equivalent amount of CO2 production. It is for now the most cost-effective way to keep CO2 from entering the atmosphere, much more so than any extractive process could match, and getting cheaper by the day.

When we are producing much less CO2, we will need to start collecting and sequestering carbon. Turning it into fuel again, by whatever means, just cycles it back to the atmosphere when the fuel is burned.

Probably the main method of capturing existing CO2 for sequestration will be geochemical.

> Emphasis on KNOWN. There's lot of research going on.

Energy crisis and climate change are happening now, the solution needs to be deployed at massive scale to replace hundreds of gigawats of generation capacity across the continent. This takes decades.

I is not possible to wait another 10 years to conplete research for a moracle solution, then another 10 years untill production scales up. A solution must be built with the tools that are avaliable now.

This is incorrect. Converting current pipelines to move H2 would be a modest investment at best.

https://www.energy.gov/eere/fuelcells/hydrogen-pipelines

> Which is a problem considering how small the H2 molecule is: we can't reuse our existing LNG pipelines.

Add carbon to it to produce methane (CH4) or higher-order hydrocarbons (butane, propane) and that's it.

With higher NOx emissions, come higher generator efficiency. Anyway, you can control both on your combustion chamber, so the claim for open fires does really not apply.

Those are just buzzwords thrown in to make their article sound more impactful and progressive. Every author does this (yes, literally every author). Who cares.

What about their tech?

Yes. The tech seems very interesting.

The key observation seems to be that atmospheric water vapor is massively purer than any terrestrial water source. And, production directly from vapor avoids efficiency and fouling problems seen when working in liquid.

I don't know what they mean by "faradaic efficiency".

Were you thinking of methane instead of hydrogen? But the paper does seem hypy. H2 will have its place, but wire transfers electrons better than hydrogen.

You miss the meat of the article.

Highly efficient production not subject to fouling makes hydrogen generated at point of use practical. H2 has myriad uses, and is gaining more at breakneck pace.