Energy

Low-cost solar-to-hydrogen cell achieves breakthrough 17.6% efficiency

Low-cost solar-to-hydrogen cel...
The silicon photocathode design in this solar-to-hydrogen cell achieves breakthrough efficiency levels using much cheaper materials than other high-performing competitors. It could be a significant step towards affordable, clean hydrogen generation.
The silicon photocathode design in this solar-to-hydrogen cell achieves breakthrough efficiency levels using much cheaper materials than other high-performing competitors. It could be a significant step towards affordable, clean hydrogen generation.
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This perovskite-Silicon dual-absorber tandem photoelectrochemical cell can convert sunlight directly into hydrogen
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This perovskite-Silicon dual-absorber tandem photoelectrochemical cell can convert sunlight directly into hydrogen
The silicon photocathode design in this solar-to-hydrogen cell achieves breakthrough efficiency levels using much cheaper materials than other high-performing competitors. It could be a significant step towards affordable, clean hydrogen generation.
2/2
The silicon photocathode design in this solar-to-hydrogen cell achieves breakthrough efficiency levels using much cheaper materials than other high-performing competitors. It could be a significant step towards affordable, clean hydrogen generation.

Hydrogen's impressive energy density offers some compelling advantages that could see it make a huge difference in the electric aviation and eVTOL sectors, as well as in renewable energy, where it's a lightweight and transportable, if not particularly efficient, way to store clean energy that's not necessarily generated where or when you need it. It's also being pushed as a means of exporting green energy, and Japan and Korea in particular are investing heavily in the idea of a hydrogen energy economy powering everything from vehicles to homes and industry.

For this to come about in a globally positive way, it's imperative that clean, green hydrogen production becomes cheaper, because right now, the easiest and cheapest ways to get yourself a tank full of hydrogen are things like steam reforming, which produces up to 12 times as much carbon dioxide as it does hydrogen by weight.

Green, renewable production methods are thus hot topics for researchers and industry, and a new breakthrough from scientists at the Australian National University (ANU) could make a significant contribution.

It's a photoelectrochemical (PEC) solar-to-hydrogen (STH) cell – a cell that takes in solar energy and water, and directly outputs hydrogen instead of powering an external electrolysis system. In this case, it puts a cutting-edge perovskite photovoltaic cell in tandem with a photoelectrode, and it works better than any similar devices that have been built, using relatively inexpensive semiconductors.

This perovskite-Silicon dual-absorber tandem photoelectrochemical cell can convert sunlight directly into hydrogen
This perovskite-Silicon dual-absorber tandem photoelectrochemical cell can convert sunlight directly into hydrogen

“The voltage generated by a semiconductor material under sunlight is proportional to its bandgap," said project lead Dr. Siva Karuturi, PhD, lead researcher at ANU's College of Engineering and Computer Sciences. "Silicon (Si), the most popular PV material in the market now, can only produce a third of the voltage needed to split water directly. If we use a semiconductor with a bandgap twice that of Si, it can provide sufficient voltage, but there is a trade-off. The higher the bandgap, the lower the sunlight capturing ability of a semiconductor. To break this trade-off, we use two semiconductors with smaller bandgaps in tandem that not only capture the sunlight light efficiently, but together produce the necessary voltage to spontaneously generate hydrogen."

One key metric here is solar-to-hydrogen efficiency, and the ultimate target, as laid out by the US Department of Energy nearly a decade ago, is 25 percent, with a 2020 milestone of 20 percent. And while cells have been designed previously that hit 19 percent, these have used prohibitively expensive semiconductor materials. Nothing that could be called affordable has managed to break the 10 percent mark until this design, which lab simulations under accepted conditions have pegged at an impressive 17.6 percent efficiency using a silicon/titanium/platinum photoelectrode.

The team says its results suggest "immense opportunities" for further optimization. The design can be made more efficient by fine-tuning the individual component designs, and it can be made even cheaper by replacing the precious catalytic metals with more abundant materials.

The end game in this space is to get truly clean, renewable hydrogen production down to prices around US$2.00 per kilogram, where it can compete head to head with dirty hydrogen and indeed fossil fuels. "Significant cost benefits could be achieved through the use of the solar-to-hydrogen approach," says Dr. Karuturi, "as it avoids the need for added power and network infrastructure necessary when hydrogen is instead produced using an electrolyser. And by avoiding the need to convert solar power from DC to AC power and back again, in addition to avoiding power transmission losses, the direct conversion of solar energy into hydrogen can achieve a higher overall efficiency for the total process."

The paper is available in Advanced Energy Materials.

Source: Australia National University via RenewEconomy

14 comments
guzmanchinky
This is exciting news, I love the idea of efficiently converting free energy into something we can use. I still wonder if charging batteries makes more sense.
martinwinlow
@ guzmanchinky - "I still wonder if charging batteries makes more sense." Of *course* it does and by a factor of at least 5... which is why H2 will never be able to compete with ever-improving battery technology except for relatively niche markets. But that is only the beginning of why H2 is, effectively, a dead duck for transportation.
Some people might feel happy flying about in an aircraft with a tank full of massively compressed H2, one of the most reactive elements known to mankind, that also happens to be one of the smallest making it next to impossible to 100% contain (leaks?), bolted in somewhere. I am not!
michael_dowling
It would be much more efficient to directly charge a battery from a solar array. The charging efficiency matches the efficiency of the solar cell:

The solar to battery charging efficiency was 8.5%, which was nearly the same as the solar cell efficiency, leading to potential loss-free energy transfer to the battery. ... This approach led to a high overall efficiency of 9.36% (average 8.52%) (Figure 2D) and storage efficiency of $77.2% at 0.5C discharge.

https://www.cell.com/joule/pdf/S2542-4351(18)30143-0.pdf
piperTom
I'm very happy to read the process is "using relatively inexpensive semiconductors." Then puzzled to find platinum listed. As far as I know, platinum is neither inexpensive nor semiconductor. What am I missing?
Peter Stegmeier
some how i just can't see using up earths water supply to power out toys as being a smart idea.
paul355
Do I understand correctly:
this is really just a cell backed into a watter splitting chamber where the solar cell(s) energy forms one side and the path to ground generates the hydrogen (and oxygen on the other side?) how is this different from conducting the electricity over to a separate device to generate the hydrogen?
George Kafantaris
To be sure, there are other important advantages aside from the impressive 17.6 percent efficiency:
“Significant cost benefits could be achieved through the use of the solar-to-hydrogen approach as it avoids the need for added power and network infrastructure necessary when hydrogen is instead produced using an electrolyser. And by avoiding the need to convert solar power from DC to AC power and back again, in addition to avoiding power transmission losses, the direct conversion of solar energy into hydrogen can achieve a higher overall efficiency for the total process." -- Siva Karuturi
DaveWesely
Charging batteries makes more sense for short term energy storage like transportation. Hydrogen, (H2) or Anhydrous Ammonia, (NH3) is a long term energy storage solution for the grid. Big picture problem is there is a shortage of wind and solar energy produced during the coldest months of the year, and an excess during the warmest. Storing electricity for 6 months with a battery is not a good solution. NH3, no problem. @Stegmeier water (H2O) is not lost, it is just separated into H2 and O2, to be recombined back into H2O when the H2 is oxidized or "burned".
drhall
Martin Winlow hit nail on head ... dude, think about it, hyped since auto electrolyzing kits hit big in 2005 ( never mind the “seven” auto computers immediately defeated the ignition settings) Plus nobody seems high on plugs for safe storage (metal hydride crystal in tanks). Lost cause, really. Solid state batteries have crossed or is crossing brittle, conduction, efficient anode/cathodes, And Soon ... Cost! Yea! Right!? H2 who’s kidding whom?
Karmudjun
Loz - pretty good article. These developments are the baby steps to improved solar utilization, and one day the 20% efficiency will look like old wasteful technology. I've seen efficiency numbers go up with modalities are married - dualsun (french company) markets pv with hydrothermal backing layer that can provide hot water while mitigating the pv panel's temperature (pv is most efficient in at the 25 C standard test temperature and for each degree above or below, it drops by 0.1 to 0.3%. If the thermal gain tracks similarly on these panels, there should be no reason not to utilize the hydrothermal backing to mitigate temps and improve efficiency.

A shout out to martinwinlow: I've read of people who were so certain that innovations would never equal proven technologies. My favorite is when some Rockefeller was marketing lubricating oil and some new lamp oil - kerosene - at the same time automobiles were starting to appear in towns without massive wealth. A stock market tip of the day was "Invest in buggy whips, the noisy and dirty horseless carriages are a fad like penny farthings and will soon disappear!" I might speculate that they thought the kerosene would never rival whale oil for smokeless light production either!