[HN Gopher] Sunlight-driven photocatalytic water splitting for h...
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Sunlight-driven photocatalytic water splitting for hydrogen
production at scale
Author : mardiyah
Score : 32 points
Date : 2021-09-24 09:28 UTC (13 hours ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| mikro2nd wrote:
| I recall from many years ago a photocatalytic process that used
| Iron/Iron-Oxide in a CSP solar setup. The solar tower superheated
| the water, splitting it; the O2 was absorbed by the Fe, leaving
| the H2 to be harvested; then the FeO2 was heated in a second pass
| to drive the O2 off, leaving the Fe to be reused. The whole thing
| sounded ingenious, and I wonder what became of the whole scheme.
| ISTR that there were some losses due to H2 and O2 recombining,
| but it sounded attractive in not needing a separation membrane as
| the OP article describes.
| dr_dshiv wrote:
| Now we can grow giant floating hydrogen-filled platforms to serve
| as the foundation for our skycities!
| dr_dshiv wrote:
| How might we use solar to produce hydrogen at a scale relevant
| for building skycities? Ok, it takes about 50kwh to produce 1
| kilogram of hydrogen from 9 kg of water. At sea level, that
| makes 12 cubic meters.
|
| One of the biggest aerostatic platforms in history was the Graf
| Zeppelin, which had a surface area of 27,299 square meters.
| Let's say the top 1/3 was covered in solar, making 1.2 kWh
| per square meter per day. In total, that's 10,800 kWh per day.
|
| So, we get 2,589 cubic meters of hydrogen a day. At that rate,
| it would take 77 days to fill the Zeppelin's 200,000 cubic
| meter capacity.
|
| Going bigger, 1 square kilometer of hydrogen is 1 billion cubic
| meters of hydrogen. At sea level, this much hydrogen could lift
| 1.3 billion kgs (600 olympic swimming pools). But at 20km, it
| can only lift 1 million kgs (1 swimming pool).
|
| Can you imagine giant bubbles growing in the sea, floating
| upwards when ready, and assembled as building materials for
| aerial architecture?
| ncmncm wrote:
| Similar tech has been demonstrated many times before, with
| varying degrees of practicality.
|
| Rather than separating the H2 from the O2, you can have microbes
| in the water eating dissolved H2, O2, and added dissolved CO2,
| and producing hydrocarbons that float to the surface for
| harvesting. You would harvest excess microbes, too, for animal
| feed. (You manage reproduction rate by control of trace
| minerals.)
|
| This system uses ultraviolet radiation. If the catalyst is
| transparent to visible light, the panels could be behind it, and
| be made more efficient by the water cooling.
| dublin wrote:
| Have you ever wondered why there are so many aliens coming to
| Earth for our water? They did this on their planets, and lost all
| their hydrogen to space. Pretty soon we'll be looking down the
| barrels of their Illudium Q-36 Explosive Space Modulators... ;-)
| Animats wrote:
| _" More rigorous safety tests are still needed, but if a properly
| designed system is used, the highly explosive hydrogen-oxygen gas
| can be safely handled for long periods."_
|
| What could possibly go wrong?
| ZeroGravitas wrote:
| I wonder how much more efficient/cheaper in theory these need to
| be than the standard PV -> electrolyser route before they make
| sense.
|
| Seems like the ability to have interchangeble electricity (which
| you can export and import to the system as needed) and the
| ability to locate the hydrogen production an aribtrary distance
| (with a transmission loss) from the energy gathering stage seem
| like a very decisive advantages, even before you consider the
| immense amounts of time and focus that are being put into
| improving PV cost and efficiency.
|
| If this method works well, you'd probably still need to consider
| whether it would make more sense to generate the light
| artificially for similar reasons.
| zizee wrote:
| A potential use for this would be to use the hydrogen as a way
| to cheaply store the energy to be used when the sun is not
| shining. I.e. Pair it with fuel cell tech to generate
| electricity at night.
|
| In this scenario the price of the tech should be compared to
| solar + batteries per kWh, and I could imagine that at scale
| hydrogen storage could beat out the cost of betteries.
| sigmaprimus wrote:
| The article mentions a 5% solar efficiency, it is my
| understanding that the current most efficient PV panels are
| around 22% solar efficient. So I would think You may be
| correct.
|
| It would be nice if they compared PV panel powered electrolysis
| hydrogen generation against this new tech.
| taneq wrote:
| I'd imagine quite a lot. The fungibility and cheap, instant
| long range transmission of electricity is worth an awful lot of
| ungainly hydrogen in a tank somewhere else that you can't use.
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