Energy

High-frequency sound waves make electrolyzers produce 14x more hydrogen

PhD researcher Yemima Ehrnst holding a simple acoustic device used to radically boost hydrogen production during electrolysis
RMIT
PhD researcher Yemima Ehrnst holding a simple acoustic device used to radically boost hydrogen production during electrolysis
RMIT

RMIT researchers say they've unlocked cheaper, more energy-efficient green hydrogen production with a new electrolysis technique boosted by sound waves. With these high-frequency vibrations active, standard electrolysis produces 14x more hydrogen.

Where batteries can't carry enough energy, or take too long to charge, green hydrogen is rising as an important zero-emissions fuel that carries a higher density of electrons and supports fast refueling. Green hydrogen is created through electrolysis; splitting water molecules into hydrogen and oxygen using renewable energy to attract each gas to a different electrode, where the hydrogen can be captured, compressed and stored.

So why does this process work so much better when the RMIT team plays a 10-MHz hybrid sound wave? Several reasons, according to a research paper just published in the journal Advanced Energy Materials.

Firstly, vibrating the water has the effect of "frustrating" the water molecules nearest to the electrodes, shaking them out of the tetrahedral networks they tend to settle in. This results in more "free" water molecules that can make contact with catalytic sites on the electrodes.

Secondly, since the separate gases collect as bubbles on each electrode, the vibrations shake the bubbles free. That accelerates the electrolysis process, because those bubbles block the electrode's contact with the water and limit the reaction. The sound also helps by generating hydronium (positively charged water ions), and by creating convection currents that help with mass transfer.

In their experiments, the researchers chose to use electrodes that typically perform pretty poorly. Electrolysis is typically done using rare and expensive platinum or iridium metals and powerfully acidic or basic electrolytes for the best reaction rates, but the RMIT team went with cheaper gold electrodes and an electrolyte with a neutral pH level. As soon as the team turned on the sound vibrations, the current density and reaction rate jumped by a remarkable factor of 14.

So this isn't a situation where, for a given amount of energy put into an electrolyzer, you get 14 times more hydrogen. It's a situation where the water gets split into hydrogen and oxygen more quickly and easily. And that does have an impressive effect on the overall efficiency of an electrolyzer. "With our method, we can potentially improve the conversion efficiency leading to a net-positive energy saving of 27%," said Professor Leslie Yeo, one of the lead researchers.

Between faster reactions, energy savings and much lower cost materials and electrolytes, the team believes its work could help bring down the price of green hydrogen.

The research is open access in the journal Advanced Energy Materials.

Source: RMIT

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15 comments
David F
Could high frequency sound waves help reduce formation of dendrites in batteries.
JeremyH
Does this mean that current (sic) electrolysis is only 2% efficient?
Rick Gutbrod
So Keanu Reeves was right in the movie "Chain Reaction"! LOL!!
S Redford
Well, it was a great headline, but actually means very little! Maximum efficiency for electrolysis of water to produce hydrogen is pushing 80% on a kWh electricity Vs higher heating value of hydrogen basis. To make “14x More Hydrogen” the original electrolysis must be terrible.
paul314
So this means potentially smaller electrolyzers for the same rate of hydrogen production? That would be cool.
PoconoPuppy
I think their flex is the increased rate (14x) and not efficiency since they imply the required energy also increased and I'm assuming it's close to 14x as well. Although by increasing rate, the equipment size is far less and therefore much cheaper to build so that helps. As does the cheaper materials, So still a win.
Adrian Akau
Sound waves probably agitate the molecules so as to give them more opportunity to align themselves properly at the contact surface.
Gordien
I wondered if there was a dramatic temperature change. Could sound help water evaporate on an evaporator pad (a side thought, I know). If hydrogen is stored as ammonia, could the hydrogen be liberated more easily and upon demand. One report I read is that hydrogen tech is dead - I hope not. I still dream of a hydrogen stream engine, used for vehicle propulsion or electrical generation. Cheap hydrogen would even be nice for water heating and cooking.
mark34
Everyone must remember that generated hydrogen is not a net energy source, it is just a carrier that is currently produced via very inefficient processes
Malcolm Jacks
Nice to see another positive project towards zero green house emissions.