Exeter team develops low-cost photoelectrode for water-splitting using sunlight | Hacker News Reader

Exeter team develops low-cost photoelectrode for water-splitting using sunlight

greencarcongress.com

131 pointsGravityloss33 comments

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.

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.

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

0.18 μmol/cm2 in 6 hours is around... 1e-60.1810000*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.

Just got to lab a few minutes ago and nobody is here yet, so why not a demo. I give you: "3.2 μL plated on a 60 cm² dish"...

https://www.youtube-nocookie.com/embed/2i7Xi9y2CFw?rel=0&amp...

n.b. this new PEC water splitting tech yields 3.2 nL/cm² H2O (nL not μL) but I don't have a pipette with that precision; so just imagine 10 of those droplets per square meter.

    .18 µmol H2O = 3.2 nL
    3.2 nL/cm² = 32 µL/m²

I understood some of those words.

The first wright brothers plane was a less efficient mode of transportation than a bicycle.

Bad example? I thought that the bicycle was _the_ most efficient mode of human transportation (provided you don't have an all-meat diet).

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.

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).

These panels as-is have such a short lifespan you'd have to replace them on a daily basis, and the efficiency appears to be several orders of magnitude lower than PV, so this is not remotely close to being cheap. Maybe this line of research will lead to an actual usable technology a decade from now (and by then battery costs will have come down enough to make hydrogen make even less sense than it currently does), maybe it's a total dead end. It's certainly not a breakthrough right now.

Why not do the math instead of rambling? A m^2 of buy it today solar can do 200 W, 3-4 hours at peak sunlight are ~700 Wh, enough to drive a Tesla 2 miles+.

Sono Motors [1] have plastered solar cells on the car body and claim that they could be able to cover 30 km of travel per day with them. Though even 10 km would be pretty helpful in a city, which is what your calculation implies (~4-5 m^2 usable surface area -> 10-15 km of additional distance).

[1] https://sonomotors.com/

Once you get past the various brand names they've applied to their technology (just go to the FAQ page), this is essentially a self-charging car, which is really cool.

Looks really interesting, specially for european cities I think. But It's a pretty expensive deal, €16k for a car without the batteries (+€4k for them).

Using my rooftop solar setup as a source of real-world numbers... Depending on time of year, an average clear day gets me between 15kWh and 25kWh generated with 18 "typical solar panels" of 230W each. Call it 1kWh per panel as a pessimistic estimate.

A Tesla Model S is quite heavy on the energy consumption because it's big and powerful. You'd expect around 0.2 kWh / km[1]. So if you're willing to go for a battery electric vehicle, a single rooftop panel could push it about 5km per day.

[1] https://pushevs.com/2016/11/23/electric-cars-range-efficienc...

No, 1m^2 @24% eff in a great location gives up to ~2kw per day (or more using very expensive panels or tracking). A Tesla get's 315 miles from 100kwh battery. So that 6.3 miles or 10,100 meters. In comparison to 0.36 it's ~28,000x as good.

I love solar, but this water splitting cell depletes over time (6 hr half life apparently) due to necessary oxidation, and must be refurbished or replaced. Your solar cell will in theory last indefinitly.

Accounting for the energy input in the annealing step, I wonder shat the cumulative power balance looks like.

Yes, being able to cheaply produce hydrogen generating panels is a huge breakthrough, but if they don't have efficiency or cost that means they can't cheaply produce hydrogen.

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.

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.

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.

It's got a home run but I hope the researchers continue to refine the work. 30% faradic efficiency, even with the material degradation, shows a lot of promise.

It seems like they were using a low intensity light source which could explain the reduced output per cm². I didn't read any specifics about light source or intensity in the original publication.

At 30%, and the fact the output can be stored directly in that form (as hydrogen and oxygen) and used in a fuel cell later when power output is required seems promising.

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

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

"10 L/m²"... not even close. It produces 32 µL/m²

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

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.

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

https://phys.org/news/2016-05-bacterium-inhales-carbon-dioxi...

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.

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 and this: https://en.wikipedia.org/wiki/Photosynthesis.

You chuckle thinking about photosynthesis?

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

Why not 2 H20 -> 2 H2 + O2?

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

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