
New Catalyst Efficiently Produces Hydrogen from Seawater - EndXA
http://www.uh.edu/news-events/stories/2019/november-2019/11112019ren-seawater-catalyst.php
======
EndXA
The original study can be found at:
[https://www.nature.com/articles/s41467-019-13092-7](https://www.nature.com/articles/s41467-019-13092-7)

Abstract:

> Seawater is one of the most abundant natural resources on our planet.
> Electrolysis of seawater is not only a promising approach to produce clean
> hydrogen energy, but also of great significance to seawater desalination.
> The implementation of seawater electrolysis requires robust and efficient
> electrocatalysts that can sustain seawater splitting without chloride
> corrosion, especially for the anode. Here we report a three-dimensional
> core-shell metal-nitride catalyst consisting of NiFeN nanoparticles
> uniformly decorated on NiMoN nanorods supported on Ni foam, which serves as
> an eminently active and durable oxygen evolution reaction catalyst for
> alkaline seawater electrolysis. Combined with an efficient hydrogen
> evolution reaction catalyst of NiMoN nanorods, we have achieved the
> industrially required current densities of 500 and 1000 mA cm−2 at record
> low voltages of 1.608 and 1.709 V, respectively, for overall alkaline
> seawater splitting at 60 °C. This discovery significantly advances the
> development of seawater electrolysis for large-scale hydrogen production.

------
sfink
Producing water vapor is irrelevant. The water will just condense and come
back out in one form or another. Produce all you want, humidity is naturally
limited.

As your linked article puts it: "water vapor does not control the Earth’s
temperature, but is instead controlled by the temperature".

------
Accujack
This is interesting for cleaning up internal combustion engine use, but it's
not so useful for climate change because although burning hydrogen doesn't
produce carbon dioxide or methane, it does produce water vapor. See this page
for info on that:

[https://www.acs.org/content/acs/en/climatescience/climatesci...](https://www.acs.org/content/acs/en/climatescience/climatesciencenarratives/its-
water-vapor-not-the-co2.html)

Also, the big issue with hydrogen as a fuel is that while it has a high energy
density per unit mass, it has a very low energy density per unit volume... IE,
from an engineering point of view you have to carry a large volume of the
stuff to have a vehicle with any significant range.

Discussion of how that could potentially be done here:

[https://www.energy.gov/eere/fuelcells/hydrogen-
storage](https://www.energy.gov/eere/fuelcells/hydrogen-storage)

In a way, this sort of research addresses the same problem as improved battery
technology - we need mobile energy sources for moving things.

I think a major reason we haven't gotten where we need to go with this problem
is that researchers tend to look for a way to replace gasoline - to find
another fuel that can simply be used in place of gas/diesel using the same
engine technology (and associated control, fuel handling, and other tech).

That's very, very difficult to do, because gasoline is uniquely suited to what
we use it for - it has high energy density per unit volume and mass, it's
moderately volatile at standard temperature and pressure, and most
interestingly we don't have to expend much energy to produce it, because all
that energy was stored aeons ago. We just have to get it out of the ground and
separate it into usable fractions. It's essentially a "free ride" as far as
energy sources go.

It's too bad continual use will destroy us.

~~~
theandrewbailey
There's also the fact that metals become brittle when exposed to hydrogen.
Hydrogen seeps through the crystal/atomic lattice and combines with oxygen or
carbon, and tears the metal apart.

[https://en.wikipedia.org/wiki/Hydrogen_embrittlement](https://en.wikipedia.org/wiki/Hydrogen_embrittlement)

~~~
syntaxing
I thought hydrogen embrittlement only effects mainly steel that under go high
temperature. That's why the rebake stuff in inert environments that was forged
like screws.

------
gwbas1c
> Zhifeng Ren, director of the Texas Center for Superconductivity at UH and a
> corresponding author for the paper, said a major obstacle has been the lack
> of a catalyst that can effectively split seawater to produce hydrogen
> without also setting free ions of sodium, chlorine, calcium and other
> components of seawater, which once freed can settle on the catalyst and
> render it inactive. Chlorine ions are especially problematic, in part
> because chlorine requires just slightly higher voltage to free than is
> needed to free hydrogen.

Which gets to one of my big questions about generating hydrogen from seawater:

I assume there will be waste products, which in the best case, is either brine
or salt. If we're making hydrogen _in mass_ from seawater, what is the
environmental impact?

~~~
contravariant
If it's just salt then it's basically just a matter of figuring out how much
seawater we need to evaporate. Which we can find out by dividing the total
energy consumption by the energy density of hydrogen [1], this results in a
figure of 120 tons a year, or about 2.8 billionth of the ocean [2], or about
.001 cm a year [3] (until the area of the ocean starts shrink noticeably).
Assuming the evaporated water returns to the ocean after a while I reckon we
should be fine.

[1]:
[https://www.wolframalpha.com/input/?i=%28world+energy+consum...](https://www.wolframalpha.com/input/?i=%28world+energy+consumption+%2F+hydrogen+heat+of+combustion%29)

[2]:
[https://www.wolframalpha.com/input/?i=%28world+energy+consum...](https://www.wolframalpha.com/input/?i=%28world+energy+consumption+%2F+hydrogen+heat+of+combustion%29+%2F+%28density+of+water+*+volume+of+the+ocean%29)

[3]:
[https://www.wolframalpha.com/input/?i=%28world+energy+consum...](https://www.wolframalpha.com/input/?i=%28world+energy+consumption+%2F+hydrogen+heat+of+combustion%29+%2F+%28density+of+water+*+area+of+the+ocean%29)

~~~
darksaints
I believe you meant to say 120 tons per second. Your [1] link shows 3.8x10^15
grams, which is 3.8x10^9 (metric) tons, not 120. That is in mass of hydrogen.
Multiply by ~9 to get the total mass of water used to electrolyze that
quantity of hydrogen.

However, the water cycle is pretty fast on average, and has incredibly high
throughput, and the cycle quickens as water vapor concentrations increase. If
hydrogen generation is sufficiently distributed, you could likely just wait
for the next rainfall to release the brine.

~~~
contravariant
You're right I seem to have misread. Good point about the factor ~9, but even
then it doesn't look like we'll be draining the oceans dry any time soon.

Although it would be a problem of unimaginable scale to use it as the sole
source of energy, which is bound to create some of its own problems, I just
don't see any obvious ones.

------
aazaa
> ... Direct electrolysis of seawater rather than freshwater is highly
> significant, especially for the arid zones, since this technology not only
> stores clean energy, but also produces fresh drinking water from seawater.
> ...

There seems to be a step missing from that statement, specifically, oxidation
of the electrolytically-generated H2 through combustion or in a fuel cell.
Assuming that step, the water is pure, and there's no need for reverse osmosis
which is itself quite energy-intensive.

This might be a key point to consider with industrial hydrogen generation
rather than, say direct capture of solar energy in a battery. Direct capture
yields energy only, whereas electrolysis of seawater yields potable drinking
water and energy.

~~~
mrspuratic
> ... electrolysis of seawater yields potable drinking water and energy.

And salts, or typically, brine. That's a harder problem to solve (i.e. dispose
of safely).

~~~
vkou
Why not just dump them right back in the ocean?

Compared to the environmental shit-show of coal and oil extraction, wringing
your hands over brine ending up in the ocean, seems entirely misdirected.

~~~
klyrs
I'd have concerns about the effects of hypersalination on the ecology local to
wherever you propose to dump this brine. This isn't "wringing hands," it's
learned caution by somebody who doesn't believe in free lunch.

~~~
vkou
So put it on a tanker, and dump it out, bit by bit, in the middle of the
ocean. This isn't a difficult problem to solve.

It is absolutely wringing hands, compared to what we do with _far more
damaging_ products and byproducts of petroleum extraction.

~~~
klyrs
And then what fraction of energy production are you spending on disposal, can
you trust the folks disposing it [1], and will it properly circulate? Ocean
currents and chemistry are extremely complex, and fisheries are an emergently
fragile food source.

I am, by no means, a fan of petroleum. But dismissing concerns about dumping
chemical waste into the ocean as "hand wringing" is not a reasoned argument.

[1]
[https://en.m.wikipedia.org/wiki/Toxic_waste_dumping_by_the_%...](https://en.m.wikipedia.org/wiki/Toxic_waste_dumping_by_the_%27Ndrangheta)

~~~
AnimalMuppet
It's not "chemical waste". It's what was _already in the ocean_.

(Yes, I know, the same thing in concentrated form is different. But dilute it
reasonably, and we're good. It's not like it's mercury or something.)

~~~
klyrs
Indeed, a better characterization is "toxic waste." Mercury, uranium, etc., is
present in ocean water and concentrating it isn't great, but it's the salt
that kills.

------
dr_dshiv
Or use a non-electrode approach, like using 13.56mhz radio frequencies to
split salt water:
[https://www.tandfonline.com/doi/abs/10.1179/143307508/270875...](https://www.tandfonline.com/doi/abs/10.1179/143307508/270875?journalCode=ymri20)

------
zentiggr
Partially in reply to Accujack but to frame the question in general:

Is hydrogen a reasonable power source for non-mobile applications? I know its
volatility makes it dangerous for household use, but are there controlled
industrial/outdoor/other uses that it would be suitable for?

~~~
jeffreyrogers
I haven't done the calculations, but my gut reaction is that you're better off
using electricity for non-mobile applications. Hydrogen production looks like:
electricity -> electrolysis -> hydrogen. And then you use the hydrogen in a
fuel cell to generate electricity. Since you already need electricity to
produce the hydrogen it seems to make more sense just to use it directly for
whatever non-mobile application you have.

There are other (cheaper) ways to produce hydrogen but they require
hydrocarbon feedstocks.

~~~
m_eiman
Storing hydrogen for seasonal use could be neat. Split water using summer sun,
use hydrogen to generate electricity in winter.

~~~
jeffreyrogers
I hadn't thought of that. One potential problem is long-term storage of
hydrogen. Hydrogen is so small that it will eventually escape from whatever
container you put it in. This diffusion is faster at higher pressures, and
depends a lot on the materials involved. So I think it could work, but you'd
have to be careful about what materials you used for your storage container.

~~~
m_eiman
Yes, it's not uncomplicated. There's a guy somewhere in Sweden running his
house in this way - he's got a bunch of hydrogen tubes in the basement that
get filled up during summer. He's obviously an enthusiast and has paid a lot
of money to build this, but at least it's somewhat practically possible.

Edit: found an article about him (in Swedish, but the images are interesting
and I think Translate would do a decent job):
[https://www.nyteknik.se/nyheter/fri-fran-elnatet-med-egen-
va...](https://www.nyteknik.se/nyheter/fri-fran-elnatet-med-egen-
vatgas-6344197)

