[HN Gopher] Sub-zero water splitting marks a new dawn for solar ...
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Sub-zero water splitting marks a new dawn for solar hydrogen
production
Author : yusuf_giftworks
Score : 186 points
Date : 2021-07-08 01:36 UTC (21 hours ago)
(HTM) web link (www.chemistryworld.com)
(TXT) w3m dump (www.chemistryworld.com)
| tacLog wrote:
| 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?
| vimacs2 wrote:
| 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.
| jessaustin wrote:
| Hydrogen is readily stored as liquid anhydrous ammonia.
| rbanffy wrote:
| I'd rather cleanup a diesel spill than an ammonia one.
| nine_k wrote:
| 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.)
| wrycoder wrote:
| Titanium hydride storage has been tested for automotive
| use. They shot hydride tanks with a rifle, and the result
| was less impressive than shooting a gasoline tank.
|
| Also, hydrogen rises quickly as it burns, instead of
| spreading out on the ground.
| ottomanbob wrote:
| Can someone qualified give an accurate upper bound to the
| potential of this innovation?
| fogihujy wrote:
| 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.
| AlexCoventry wrote:
| 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 wrote:
| 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?
| TaylorAlexander wrote:
| My understanding is that hydrogen likes to leak because its
| atoms are smaller than the atoms of anything we'd contain
| it with. Though there are chemical ways to store it and I'm
| not familiar with those.
| KMag wrote:
| I think reversibly combining hydrogen with nickel to form
| nickel hydride is one solution that's been proposed for
| hydrogen vehicle fuel tanks.
| maliker wrote:
| 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.
| xenonite wrote:
| Original Publication:
|
| Kolbach, Rehfeld, May: "Efficiency Gains for Thermally Coupled
| Solar Hydrogen Production in Extreme Cold", Energy &
| Environmental Science, 2021.
|
| https://doi.org/10.26434/chemrxiv.14377049
| alpineidyll3 wrote:
| 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.
| [deleted]
| yc12340 wrote:
| 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 wrote:
| > 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.
| bpodgursky wrote:
| 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_k wrote:
| 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.
| XorNot wrote:
| The sheer amount of hydrogen you would have to put into the
| atmosphere for this to become a problem is _enormous_.
|
| This is a problem in the same sense that the sun going red
| giant is a problem.
| JumpCrisscross wrote:
| > _This is a problem in the same sense that the sun going
| red giant is a problem_
|
| To be fair to OP, at the point we're concerned about
| Exxon Valdez circa 2400 dumping an atmosphere of hydrogen
| into space _and_ the Sun 's expansion, we could solve one
| problem with the other and bring the Sun's mass over.
| rbanffy wrote:
| If we learn how to remove mass from the Sun at a large
| scanner, we can extend its useful life and fuse the
| hydrogen into more useful materials. We can prevent it
| from going red giant in the first place.
| Robotbeat wrote:
| That's not really true. Hydrogen oxidizes in the
| atmosphere, whereas helium does not. Also, helium is
| continually produced via nuclear decay in the Earth, and it
| seeps up through the crust. So it's rare and it leaks into
| space with or without humans.
| GravitasFailure wrote:
| 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.
| SlowRobotAhead wrote:
| I think scale is a really hard thing for us, but yes, being
| concerned about this is quite silly.
| vimacs2 wrote:
| 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.
| alpineidyll3 wrote:
| 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.
| vimacs2 wrote:
| I assume by "life", you mean post-industrial revolution
| humanity which shouldn't be treated as the norm, for either
| life nor even human history.
|
| It's also irrelevant, water is incredibly abundant in our
| solar system and we don't even have the largest oceans on
| Earth, they're just the largest ones on the surface.
| jodrellblank wrote:
| Are you saying there's an underground ocean bigger than
| the Pacific?
|
| Where is it?
| fogihujy wrote:
| The oceans on Europa cover a smaller area than Earth's
| oceans, but they contain a larger volume of water as
| they're much deeper.
| vimacs2 wrote:
| Yes and Ganymede appears to contain concentric layers of
| oceans separated by layers of ice. There is also
| Callisto, Encaeladus, Titan, and since New Horizons,
| potentially even Pluto - not to mention that the trace
| amounts of H20 present in the sun would outweigh all of
| it a thousand fold.
|
| Bottom line is that water is never in short supply.
| Nitrogen is likely to be the real bottleneck in our
| future efforts at colonisation and terraforming - at
| least till if/when we master star lifting of resources.
| At that point, mass and energy no longer make meaningful
| limiters and waste heat disposal becomes the primary
| menace to further development.
| fogihujy wrote:
| It's mainly a logistics problem; there's more than enough
| nitrogen in the Solar system.
|
| We just need to solve the simple problem of moving it
| from the atmosphere of Venus to where we want it to be.
| ;)
| vimacs2 wrote:
| You're correct in the short term but Venus only has four
| times the nitrogen content of Earth which might sound
| like a lot for now but in a fully developed Dyson swarm,
| will prove to be inadequate. It might turn out to be a
| non issue since we might be able to simply transmutate it
| into existence by recycling more abundant materials with
| fusion but there is still a lot of unknowns with the
| actual engineering constraints of controlled fusion.
| labster wrote:
| I feel like proton pumps have been used by life for
| billions of years already and everything is mostly fine?
| Robotbeat wrote:
| 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.
| zentiggr wrote:
| 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.
| jandrese wrote:
| 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 wrote:
| I've seen lots of opinion here but no one has whipped out a
| spreadsheet and run some numbers.
| jandrese wrote:
| Energy required to Elecrolyze the world's oceans.
|
| Theoretical max efficiency: 13.173 MJ/kg of water.[1]
|
| Water in the oceans: 1.35E21 kg [2]
|
| Total energy needed to electrolyze the oceans: 1.77E22 MJ
|
| Total energy recieved by the Earth from the sun per second:
| 4.3E14 MJ
|
| Time required to elecroyize the oceans using the entire
| available output of the Sun on Earth at 100% total
| efficiency: 478.67 days
|
| It is a very silly idea to think that we could accidentally
| wield many orders of magnitude more energy than humanity
| has ever harnessed in collective history without noticing.
|
| [1]
| https://physics.stackexchange.com/questions/24624/water-
| elec...
|
| [2] https://mathblag.wordpress.com/2013/08/03/how-much-
| water-is-...
| obiwanpallav1 wrote:
| 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.
| unchocked wrote:
| 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_k wrote:
| 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.
| matzab wrote:
| 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 (70.68degS, 8.27degW, Tavg,y = -15.5 degC)
| would prospectively require a module area of 0.41 m2, whereas
| at Paranal observatory (Chile, 24.63degS, 70.40degW, Tavg,y =
| 0.4 degC) 0.18 m2 would suffice._
| wrycoder wrote:
| 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.
| thereisnospork wrote:
| >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
| 10degC.
|
| 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 wrote:
| 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.
| thereisnospork wrote:
| 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.
| mlyle wrote:
| It has to be more -cost- efficient, not more
| thermodynamically efficient.
| thereisnospork wrote:
| One tends to follow the other.
|
| Arguing that, in the judgement of process for the
| conversion of one form of energy (sunlight) to another
| (hydrogen), thermodynamic efficiency, or the measure of
| _how well a process converts one form of energy to
| another_ isn 't relevant is somewhere between obnoxiously
| pedantic and wishful thinking.
|
| Funnily enough I read the article after your comment, and
| it is even less useful, interesting, than my initial
| assessment (not even direct solar to H2). It has
| approximately the novelty and utility of porting DOOM to
| <insert processor here> and running it in a refrigerator.
| angus-prune wrote:
| In the real world energy isn't always fungible. The
| location of the energy can be an important factor in
| something's overall efficiency.
|
| If you need the end product at a particular location, the
| transport costs can overwhelm any differences in
| efficiency.
|
| The same also applies if you have excess energy in a
| particular location that you want to use.
|
| In either case, the transport costs can make using the
| less efficient process, the more energy efficient choice
| overall.
| new_realist wrote:
| No, it doesn't; it just has to cost less, overall.
| Efficiency is only a weak proxy for cost.
| clomond wrote:
| *unless we are talking about energy systems and therefore
| VARIABLE costs matter significantly.
| wiz21c wrote:
| And cost is sure not a proxy for efficiency.
| mrpopo wrote:
| Not if you want to consider environmental impact.
|
| The petrol in the ground is free, sunlight is free,
| biodiversity is free. The cost is only a human factor.
|
| Higher efficiency on the other hand usually means lower
| resource consumption.
| johnchristopher wrote:
| Why is that downvoted ? You might have the cheapest
| energy source, if it's not efficient enough to meet
| demand without ruining the environment for humans then
| it's not good.
|
| A weak proxy for cost ? Or a strong one for survival ?
|
| A cheaper steel bike is less efficient than an expensive
| carbon fiber bike when your goal is to get to the
| mountain top before the flood submerges the valley.
| AtlasBarfed wrote:
| 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.
| ArkanExplorer wrote:
| But we're already going to be building those batteries
| anyway: Electric cars.
|
| What we need is a proper international standard for cars to
| be able to interact with the grid, to be able to charge and
| discharge based on grid conditions and pricing.
|
| Its stupid to have everyone coming home from work at 6pm
| and plugging in their cars to charge right at the existing
| afternoon demand peak, when solar is waning. Just getting
| those cars to delay charging until around midnight
| (allowing user override) would shift a huge amount of peak
| demand.
|
| Same concept if you don't use your car during the day - it
| should be able to discharge right into the morning and
| afternoon peaks, at your control. The user should be
| credited for this onto their car account.
|
| It might even make sense to have dedicated high-voltage
| circuitry in houses and apartment blocks, to be used for
| EVs, solar, etc.
|
| And we should really figure that out immediately since EV
| production is ramping up right now. We can't just rely on
| single automakers (Tesla) to work out these societal
| problems.
| UnpossibleJim wrote:
| If we're going to try and ramp up battery production and
| technology, then in for a penny in for a pound. We should
| really decentralize the power grid enough to take the
| weight of these types of spikes, putting in batteries to
| the home (like the Tesla wall, but with more competition)
| and solar/wind/gravity generation to supplement grid
| power generation. It's a jobs program that's been needed
| and called for for the last few years anyway, and now
| seems the time... not that the governmental gridlock
| would ever let anything like that happen, or even a
| spending project for small equity home/apartments
| retrofitting would happen. Not to mention the raw
| materials needed for the batteries.
| londons_explore wrote:
| So far, batteries are pretty competitive on the "store
| energy for 24 hours" time horizon - where you need to power
| something at night with solar collected in the day, or
| evening out peaks and troughs in the electricity grid.
|
| But it isn't yet competitive with "store energy collected
| in the summer for use in the winter".
|
| For that usecase, far more energy must be stored for far
| fewer dollars to make it competitive vs just having a big
| fuel tank and a winter-only diesel generator.
|
| Keeping lakes of water for a few months for hydropower are
| also competitive - the storage capacity of a big lake on a
| mountain top is immense.
| AtlasBarfed wrote:
| If CATL and other LiFePO battery makers get them to
| 200wh/kg, which they teased in 2020, and they maintain
| the same cycle endurance, temperature range, safety, and
| cost advantages, it will be a real game changer.
|
| I've heard pumped water is like 90% efficient, but you
| need a gradient and space.
|
| Does wind power decrease in winter? I also remember
| schemes for making a huge solar farm in the Sahara and a
| superconducting conduit to Europe, and that was several
| paradigm shifts in solar cell performance ago (15 years).
| But almost all large countries seem to have a
| sufficiently sized desert to do this with (US, Russia,
| China).
|
| If solar gets good enough, and it is still on some prime
| parts of the economies of scale price drops, you don't
| care as much about long-distance transmission loss.
| darksaints wrote:
| They might be in a race to win certain markets, but they
| are most definitely both viable in their own respects in
| other markets. Fuel cells will likely never be used in
| watches and phones, and batteries will likely never be used
| in widebody jets.
| usrusr wrote:
| 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.
| darksaints wrote:
| 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.
| skoocda wrote:
| 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.
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