Sub-zero water splitting marks a new dawn for solar hydrogen production

https://www.chemistryworld.com/news/sub-zero-water-splitting-marks-a-new-dawn-for-solar-hydrogen-production/4013887.article

by yusuf_giftworks • 5 years ago

193 70 5 years ago

chemistryworld.com

tacLog2• 5 years ago

Paywall free link: https://web.archive.org/web/20210708014033/https://www.chemi...

First off this seems like a really important addition to solar in general. My impression is that hydrogen is easy to make, can be a closed water cycle (uses the same water it generates to when release the energy), and the only downside is the inefficacies of compressing it to store it among the other steps.

Does anyone know if this would be a practical source of heat say at night, considering what I understood to be Hydrogens lower energy density?

For example, I was wondering roughly how big of a tank of (I am assuming) liquid hydrogen would be required to match say 50 a gallon tank of diesel.

Or am I missing something here?

vimacs26• 5 years ago

There isn't a paywall I can spot in the original link - perhaps it's a regional thing?

What you might be missing here is that the "only downside" should be emphasized far more. Hydrogen is a bloody nightmare to store long term. It's boiling point makes the -20 C involved with this technology look like an oven and you really do want to ideally store it as a liquid since the exceptionally low molecular weight means leakage is a constant problem save for some very advanced (and expensive at scale) carbon composites.

Graphene seems to be a potentially excellent storage medium but we are still a while off from being able to manufacture that at the amount that would make it economically usable for hydrogen storage at scale.

nine_k3• 5 years ago

One way to store hydrogen safely long term is metal hydrides. Hydrogen readily infuses certain metals, like lithium, like water infuses a sponge.

The problem is that the density us rather low. Enough to store tritium in a nuclear warhead, but possibly a bit bulky for home use. (Also, the hydride remains flammable.)

jessaustin2• 5 years ago

Hydrogen is readily stored as liquid anhydrous ammonia.

ottomanbob• 5 years ago

Can someone qualified give an accurate upper bound to the potential of this innovation?

AlexCoventry• 5 years ago

I'm not qualified, but "The technology could serve as a renewable fuel source in high altitude and polar environments" from the first paragraph of the article suggests to me that the potential is pretty limited.

e12e• 5 years ago

I wonder about the storage though. One would need to produce during summer/polar day for use in winter/polar night - is it feasible to store large quantities of hydrogen for 6 months?

fogihujy4• 5 years ago

I suspect it'd be most practical in areas with limited heat and were other alternatives aren't as handy.

There's also a few areas where combustion engines are more practical than electric ones and hydrogen engines could be used as a stop-gap solution until electric alternatives catch up; there's only so much humanity can do at once and using combustion engines with renewable fuels could reduce emissions while we take our time focusing on other areas.

alpineidyll32• 5 years ago

Just as burning fossil fuels cause dangerous reconfiguration of earth's atmosphere, I think that the idea of a hydrogen economy requires careful thought. Hydrogen shares with helium a unique property, that it is at escape velocity at the temperatures of the upper atmosphere. It seems unfathomable now, but if we converted all earths water into hydrogen and oxygen without containment, the planet would become a dead rust ball. It's not that these technologies should not be pursued, merely that adopting any technology on a planetary scale, should require some incredibly serious consideration.

bpodgursky• 5 years ago

This would only be relevant when the fuel leaks, right? During normal combustion the hydrogen is never exposed to the open atmosphere, it is burned back into H2O and released in that form.

nine_k3• 5 years ago

Yes. But one should be aware that leaking some hydrogen is leaking it to the outer space, for good.

This realization does not stop us from using much more rare helium in party balloons, though.

GravitasFailure• 5 years ago

Losing Earth's hydrogen to space would require a stupendously long wait. Maybe freeing all of it at once would help speed the process asking, but the first lightning strike, volcanic eruption, or meteor would just ignite it all back to water. I'd be far more worried about getting struck by lighting, a volcanic eruption or a meteor, than losing our hydrogen to space.

vimacs26• 5 years ago

A civilisation capable of significant depletion of the earth's oceans for the production of hydrogen and oxygen is so far ahead of us in economies of scale that we would be long past the point of needing to worry about something that could (to the point of view of such a civilisation) be trivially solved with an air wall or a secondary low earth orbit artificial magnetosphere.

alpineidyll32• 5 years ago

I think you should look at plots of CO2 emissions over time. Life is very efficient at exploiting resources in an exponential fashion, when they become available.

Robotbeat2• 5 years ago

It's worth pointing out that hydrogen oxidizes in the atmosphere, unlike helium, so it won't escape as readily. Secondly, the Sun already splits water into hydrogen and oxygen with UV at some low rate, and that has been going on for literally billions of years from now. I don't think this aspect of what you're talking about will matter before 200 million years from now or so when the Sun becomes intense enough to kick off runaway greenhouse effect (even without human effects) unless we produce so much hydrogen (and leak it) that waste heat of civilization becomes the limiting factor.

There are other things to worry about.

jandrese2• 5 years ago

I just love the thought of some silly human not putting the gas cap on correctly and whoops, we've allowed all of the hydrogen in all of the Earth's oceans to escape and now the atmosphere is way over-oxygenated and everything is always on fire.

It's like worrying that astronomers won't be able to enjoy the night sky after we've built a Dyson Sphere.

quickthrower2• 5 years ago

I’ve seen lots of opinion here but no one has whipped out a spreadsheet and run some numbers.

yc12340• 5 years ago

It is incredible, how HN community (arguably made from some of the lest dumb people on Internet) can turn blind eye to this major concern while laughing and patting themselves on their backs.

I guess, industrial magnates of 1800s would have shown the same reaction, if someone told them about dangers of burning fossil fuels.

"This is ridiculous!", "But Sun was causing fires for centuries!" and "If it gets bad, we can stop burning more coal!" — those excuses didn't age well, yet most replies to this comment repeat them almost verbatim.

Of course, instantly sending all (or most) of Earth hydrogen into outer space is impossible — at the current technology level. But wasting what little water we have to make it is still a bad idea.

Many places are already short on fresh water — the kind of water, necessary for electrolysis. We can make hydrogen from saltwater too — after purifying it, but that's not commercially viable. No one uses "free" energy from solar panels to make new lakes or refill depleting aquifers.

Most of the Earth's surface is covered by water, but we can't even purify enough to satisfy our biological needs — otherwise Sahara would be a major agricultural and economical attraction. To solve world's water problem would require near-unlimited power, and the hydrogen production is not going to do it. At best, a hydrogen boom would result in another round of colonial robbery: stealing water from people, who can't defend it, to power more air conditioners in USA and Europe.

perilunar• 5 years ago

Of course, instantly sending all (or most) of Earth hydrogen into outer space is impossible — at the current technology level. But wasting what little water we have to make it is still a bad idea.

The whole point of making hydrogen (from water) to store energy is so we can release the energy later — by oxidising it back into water. We get the same amount of water back afterwards. No one is going to be stealing water to make hydrogen.

zentiggr• 5 years ago

If we as a species develop enough to be able to electrolyze a significant enough portion of all of Earth's water for this problem to arise, it's almost a given that we have developed technologies that no longer require us to stay on Earth.

Plus hydrogen chemistry, as others have mentioned, will stop at least 99% of the losses you propose simply by reoxidizing in the presence of free oxygen.

Helium is inert and doesn't react, therefore is much more likely to be lost to diffusion.

unchocked• 5 years ago

I'm excited about anything in electrolysis/fuel cell development, but the figure of merit is efficiency. It's neat to use sulphuric acid to reduce the freezing point of your electrolyte solution, but if it's not efficient you might as well just heat your electrolyzer.

Nothing is a power system without efficiency figures. Otherwise it's just a chemistry experiment.

nine_k3• 5 years ago

Since it uses two catalysts and controls for heat production (and loss), it must be pretty efficient, more so than straightforward electrolysis.

It can be slower to produce the gasses, though. High efficiency, low throughput.

wrycoder2• 5 years ago

Exactly. Hydrogen electrolysis is most efficient at elevated temperatures, and that was a problem in some exceptionally cold areas.

This is a development that makes electrolysis practical in those regions.

thereisnospork3• 5 years ago

This is a development that makes electrolysis practical in those regions.

It is neither a development[0] nor does it particularly make electrolysis practical in those regions[1] (or more so than it was yesterday). Unless there is something about keeping solar cells warm that is beneficial, I'm really not seeing it.[2]

Hydrogen electrolysis is most efficient at elevated temperatures

negligibly until you get into the realm of solid oxide cells (100's of C) -20 to +40 is negligible, and moreover a moot point because of [1]

[0]>> The method works by using electrolytes with low freezing points, such as dilute sulfuric acid, to allow the use of water at lower temperatures.

A common electrolyte for making H2, at room temperature and otherwise. Not novel (or interesting).

[1]>> resulting in an interior working temperature of around 10°C.

Approximately 30-40 percent inefficiency in an electrolyzer manifests as heat -- all they did here is wrap their electrolyzer in a blanket. Any electrolyzer of appreciable (read: useful) power has trouble keeping cold, not warm. The square-cube law applies here, electrolyzer power (and heat generation) scales w.r.t. volume, heat loss with area. For intuitive purposes, a device capable of fueling a car (driving 24/7) would be outputting about as much heat as that car's engine.

[2]There might be, (chemistry is my meat and potatoes, more so than physics), but I've always seen the issue being more with keeping solar cells cool.

roughly• 5 years ago

Depends. If the purpose of this is to take sunlight when it’s abundant and turn it into hydrogen as a storage mechanism, then the efficiency of the exchange may not matter as much.

thereisnospork3• 5 years ago

Efficiency always matters; opportunity costs. If sunlight to hydrogen is your goal a novel solution has to at bare minimum be more efficient than solar PV -> electricity -> electrolyzer[0] to be useful.

[0]Known, boring technology with 99.9% of the engineering warts and technical debt already solved.

AtlasBarfed2• 5 years ago

Hydrogen is in an economic race with batteries in storage. Hydrogen is hard to store in tanks and has a higher thermodynamic loss and the fuel cells are expensive. Batteries are big and expensive.

So the efficiency of hydrogen split-store-generate needs to beat the efficiency of store-release of the battery and the costs of the equipment.

matzab• 5 years ago

This is explicitly aimed at producing energy in cold environments (high altitude, polar regions), so it's less of an issue (and not exactly the point). Anyway, they seem to aim at 12% STH efficiency and provide some examples (assuming 65% hydrogen fuel cell efficiency):

Then, powering a Raspberry Pi computing device (PRPi = 4W) for an autonomous measurement device year-round at the > Neumayer III station (70.68°S, 8.27°W, Tavg,y = −15.5 °C) would prospectively require a module area of 0.41 m2, whereas at Paranal observatory (Chile, 24.63°S, 70.40°W, Tavg,y = 0.4 °C) 0.18 m2 would suffice.

darksaints2• 5 years ago

The figure of merit is cost, and it's only correlated with efficiency. If efficiency was king, we'd all be driving 60% efficient cars...the technology exists but the cost is not acceptable.

usrusr• 5 years ago

Agreed, compared to a novel chemical approach isolation and counterflow heat exchange seem almost embarrassingly lowtech to the mostly hypothetical "how to to electrolysis when it's cold outside" problem.

Perhaps there might be some actual merit when the end product of your process is compressed/liquefied H2? Still reads more like the usual make up some hypothetical use case for the highly impractical niche you chose to push the boundaries of scientific knowledge. But who am I to judge, I did semantic web in multi-agent systems back when ai was symbolic.

obiwanpallav1• 5 years ago

How will it impact the current Solar energy sector?

Two of the major pain points were the erratic weather refusing to generate energy because of sun's availability and the storage of energy for particularly those cold areas where it was expected that entire energy for an year can be saved inside the batteries that can be generated in 2-2.5 months.

xenonite• 5 years ago

Original Publication:

Kölbach, Rehfeld, May: "Efficiency Gains for Thermally Coupled Solar Hydrogen Production in Extreme Cold", Energy & Environmental Science, 2021.

https://doi.org/10.26434/chemrxiv.14377049

maliker• 5 years ago

I work for electric utilities, and we've been looking at hydrogen carefully this year, but it looks to remain a niche technology for energy storage.

Hydrogen production (electrolysis, etc.) is only about 30% of the full system cost since you've also got storage and generation components. It's not likely that hydrogen will become competitive with battery energy storage since the full systems costs are very similar now, batteries are rapidly dropping in cost, and hydrogen storage and generation tech isn't getting much cheaper.

There could be a cost-competitive niche role for hydrogen through injection into existing natural gas infrastructure. But that infrastructure is already facing cost pressure from renewables.

skoocda• 5 years ago

It's worth noting that regardless of this development, hydrogen fuel cells still do not work well in sub-zero temperatures unless they are operated in perpetuum.

When you decide to shut down your fuel cell and the temperature of the system drops below zero, water will freeze on your micron-thick platinum catalyst; cracking it, and rendering the entire fuel cell useless.

jbj• 5 years ago

Is it common perception that "sub-zero" refers to temperature degrees below 0°C and/or 0°F?

Sub-zero water splitting marks a new dawn for solar hydrogen production

Related Stories