
Exeter team develops low-cost photoelectrode for water-splitting using sunlight - Gravityloss
http://www.greencarcongress.com/2018/05/20180509-exeter.html
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mchannon
Many of the comments in here are getting hung up on efficiency.

Do you know how efficient your car is? Your water heater? No, and it's not
because those figures are important. What actually matters is how much it
costs you to travel each mile and how much it costs you to have hot showers.

It's cost per kilo that matters, and that's it.

Carpet the grounds outside an oil refinery with this stuff and you might, just
might, have a worthy competitor to natural gas-formed hydrogen used in
hydrotreating, with a fair amount of development on this technology. A Bergius
process might likewise benefit.

Right now, the billion dollar question is will this ever outcompete PV-powered
electrolysis? PV panels are ridiculously cheap, bound to get cheaper, and they
would appear to be better suited to making and concentrating hydrogen at the
high pressures needed.

The notion that this could power your Mirai is doubtful, because the energy
input necessary for the hydrogen pressurization the Mirai requires is equal to
or greater than the energy content of the hydrogen itself.

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Retric
Efficiency can be a good proxy for cost. If this was 20,000 times as efficient
solar cells would still win, but cost might make the difference. Without that
you would need square miles of this _per car_ which is just not going to
happen.

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endymi0n
Let me quickly do the math to some more useful units:

0.18 μmol/cm2 in 6 hours is around... 1e-6 _0.18_ 10000*2 == 0,0036 grams of
hydrogen for a square meter of panel on a day of sunlight.

That will move a Toyota Mirai (~1kg H2 for 100km) around 36 centimeters far.

Call me not convinced yet. Cool chemistry though.

~~~
talltimtom
And for a typical solar panel you’d get what, 50m? Are you also not convinced
about solar tech in general? Being able to cheaply produce hydrogen generating
panels is a huge breakthrough, even if they do not yet have the efficiency or
cost that would allow them to enter the market.

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endymi0n
Why the snark? Let's do the math real quick - a square meter of photovoltaic
panel will give you an averaged 4 kWh per day, which gives you around 80 grams
of hydrogen via electrolysis. That gives you 8 km of driving a Mirai with
current indirect technology.

So whatever you're reading into my post, you're probably wrong (I'm a big
advocate of green tech).

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bmcusick
Here's the bigger issue than efficiency, IMO:

> during the first 6 hour cycle where the photoelectrode generated 0.18
> μmol/cm2 of hydrogen

And then...

>After a further 6 hours illumination, the LaFeO3 thin film generated 0.08
μmol/cm2 of hydrogen (Figure S8). This provided additional evidence that the
film is re-useable, although the amount of hydrogen produced is almost halved

From 18 to 8 units/area in just six hours is not a good decay curve.

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bufferoverflow
It really depends on how cheap that electrode is. If it's a few pennies,
nothing stops you from automatically swapping it every couple of hours.

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adrianN
It only produces microliters of hydrogen/cm^2 in six hours and the amount of
hydrogen produced was cut in half after that. Doesn't sound very promising to
me.

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Gravityloss
Square centimeter is a tiny area though. Centiliters per square meter!

~~~
whatshisface
1 mL/cm^2 is actually equal to 10^-3 L (10^2)^2 / (m^2) = 10L/m^2.

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adrianN
But the apparatus only produces 1µL/cm^2.

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syntaxing
Developing an efficient way to produce hydrogen is actually really important
since it's pretty difficult. From what I remember from grad school, over 70%
of hydrogen used is produced from high pressure steam with turbines since its
the only energy efficient and scalable way to create hydrogen. The lack of
renewable hydrogen is actually hindering a lot of technology (such as fuel
cell) since not many can produce it easily.

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ncmncm
Much more interesting than production of hydrogen (which has been achieved
elsewhere: [https://phys.org/news/2011-09-artificial-leaf-fuel-
sunlight-...](https://phys.org/news/2011-09-artificial-leaf-fuel-sunlight-
video.html)) is integrated production of stuff more useful than hydrogen.

[https://phys.org/news/2016-05-bacterium-inhales-carbon-
dioxi...](https://phys.org/news/2016-05-bacterium-inhales-carbon-dioxide-
hydrogen.html)

You can grow bacteria in the same water, and given CO2, they produce and
excrete hydrocarbons. Daniel Nocera uses Ralston eutropha bacteria, and a
different catalyst.

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indoorfish
Maybe it's related to my training in bio-engineering, but I've seen similar
concepts and I often chuckle thinking about this:
[https://en.wikipedia.org/wiki/Transpiration](https://en.wikipedia.org/wiki/Transpiration)
and this:
[https://en.wikipedia.org/wiki/Photosynthesis](https://en.wikipedia.org/wiki/Photosynthesis).

~~~
subroutine
You chuckle thinking about photosynthesis?

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porky
So, H2 and O2 are created? The O2 comes from 1xO from the electrode?

~~~
nsuser3
Why not 2 H20 -> 2 H2 + O2?

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perplexenginerd
From the paper:

"Conclusion: In summary, we have developed a stable p-type LaFeO3
photoelectrode with a coral like nanostructure by a novel and inexpensive
spray pyrolysis technique with a post annealing step, which yields a
photocurrent density of 0.16 mA/cm2 at 0.26 V vs. RHE. Chronoamperometric
studies showed that the LaFeO3 film provides a stable p-type response over a
21 hour period. Optical and impedance data showed that the material is able to
straddle the redox potential of water, with the valance band at 1.29 V and
conduction band at −1.11 V, and a bandgap of 2.4 eV. IPCE studies revealed
that the photoelectrode had an APCE of 3.5%. Water splitting test was
conducted in a custom made reactor vessel, where the working electrode and Pt
counter electrode was connected by a single looped wire, without any external
bias being applied. This in turn yielded 0.18 μmol/cm2 hydrogen after six
hours during the first cycle with faradaic efficiency of 30%. To the best of
our knowledge this is the first time hydrogen zhas been produced spontaneously
during a water splitting test without any external bias being applied using
LaFeO3 photoelectrode as a single material. These findings demonstrate that
LaFeO3 is a potential candidate to act as a photoelctrode for unassisted PEC
water splitting to generate solar fuel (hydrogen) cost effectively. However
further work is required to investigate and improve slow charge carrier
dynamics and low light absorption chal-lenges of LaFeO3 photoelectrodes"

DOI:10.1038/s41598-018-21821-z

