Chemical engineers borrow technique to store solar energy

Chemical engineers borrow technique to store solar energy
Graphic shows how electrolysis could produce hydrogen as a way to store renewable energy. During the day, solar panels supply surplus electricity for electrolysis, producing hydrogen. At night, hydrogen would be combined with oxygen from the air to generate electricity.
(Phys.org) —Chemical engineers at Stanford have designed a catalyst that could help produce vast quantities of pure hydrogen through electrolysis – the process of passing electricity through water to break hydrogen loose from oxygen in H2O.

Today, pure , or H2, is a major commodity chemical that is generally derived from natural gas. Tens of millions of tons of hydrogen are produced each year; industrial hydrogen is important in petroleum refining and fertilizer production.

Chemical engineering Professor Thomas Jaramillo and research associate Jakob Kibsgaard want to use electrolysis to do things such as producing H2 from water and using the process to store solar energy. But to industrialize water-splitting they must find a more cost-effective process.

Electrolysis in classroom experiments is simple: lower two metal electrodes into water; when electricity is passed through these electrodes they act as catalysts to break water molecules into bubbles of hydrogen and oxygen gas.

Platinum is the best for producing hydrogen through water electrolysis. But to make electrolysis an industrial process a cheaper electrode must be found. "We're trying to make H2 in the most efficient way possible without using precious metals," Jaramillo said.

In the German scientific journal Angewandte Chemie, Jaramillo and Kibsgaard describe a cheap, durable and efficient catalyst that could take the place of platinum.

Their ambitions go beyond using electrolysis merely to replace the current market demand for hydrogen.

Right now there is no cost-effective, large-scale way to store solar energy. The Stanford researchers believe that electrolysis could turn tanks of water into batteries for storing solar energy. During the day, electricity from solar cells could be used to break apart water into hydrogen and oxygen. Recombining these gases would generate electricity for use at night.

Electrolysis uses electricity to crack the chemical bonds that hold H2O together.

Cracking the chemical bonds of water produces a – a proton with no electron to balance it out. A good H2 catalyst gives the proton a place to stick until it can pick up an electron to form a hydrogen atom on the catalyst surface and then pair up with a neighboring hydrogen atom to bubble off as H2.

The trick is finding a catalyst with the right stickiness.

"If the binding is too weak, the ions don't stick," Jaramillo said. "If it's too strong, they never get released."

Platinum is perfect but pricey. Last year the Stanford engineers discovered that a version of molybdenum sulfide, a catalyst widely used in petrochemical processing, had some of the right properties to serve as a cheap but efficient alternative to platinum.

Jaramillo explained that petrochemical processing has similarities to electrolysis. That's because petroleum feed stocks, such as tar sands, contain a significant fraction of heavy molecules. Petroleum refineries use catalytic reactions that involve hydrogen to crack these heavy molecules into lighter molecules like gasoline.

Similarly, electrolysis involves cracking water molecules, or breaking apart their . As the Stanford engineers sought to improve on their own discovery they found an even better way to produce hydrogen from water by taking yet another page from the petrochemical playbook.

Petroleum processing often involves scrubbing sulfur out of fuels to reduce acid rain. During this scrubbing process, some of the sulfur atoms get incorporated into petroleum processing catalysts, increasing the activity of these catalysts.

This gave the Stanford engineers an idea: If they laced an already good catalyst with sulfur atoms, would it become an even better electrode for producing pure hydrogen?

They chose to add sulfur atoms to a catalyst called molybdenum phosphide, which is known to speed up hydrogen production though electrolysis.

Adding the created a new catalyst – molybdenum phosphosulfide– that was more effective at producing hydrogen than its predecessor.

The new sulfur-laced catalyst was more durable, which is vital in an industrial process where the electrode must function day in, day out, without degrading, just like the noble metal platinum.

The molybdenum phosphosulfide catalysts developed by Kibsgaard and Jaramillo are a major advance. As electrodes they are remarkably stable with an efficiency approaching that of platinum.

Now, members of Jaramillo's group are working to improve this new catalyst. For instance they are engineering the material at nano-scale dimensions to catalyze the reaction more effectively. Other research initiatives include incorporating this catalyst into bench-top prototypes of future energy storage systems. The idea would be to use water to store by day in the form of H2 and then, at night, to recombine hydrogen and oxygen into , generating electricity in the process.

Jaramillo noted that the findings in this and the prior scientific paper pursue environmentally friendly energy strategies, but they are based on ideas borrowed from petrochemical plants.

"It's exciting to make these connections between really different areas of technology," he said, "and aim to operate at the meta-level of science."


Explore further

Researchers teach old chemical new tricks to make cleaner fuels, fertilizers

More information: "Molybdenum Phosphosulfide: An Active, Acid-Stable, Earth-Abundant Catalyst for the Hydrogen Evolution Reaction." Angew. Chem. Int. Ed.. doi: 10.1002/anie.201408222
Citation: Chemical engineers borrow technique to store solar energy (2014, November 6) retrieved 26 June 2019 from https://phys.org/news/2014-11-chemical-technique-solar-energy.html
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Nov 06, 2014
Would lithium lined tanks keep so much hydrogen from leaking through the tank walls? Not as small as hydrogen atoms, but much smaller than iron atoms.

Nov 06, 2014
It does not make sense to convert electricity to hydrogen then back unless efficiency is super high.

For stationary, perhaps alum battery is way better.

Nov 06, 2014
The same enhancement for electrolysis could be used with offshore wind farms. Only, there what would happen would be that the hydrogen would be piped to shore for use - in industry or to power vehicles. This would replace all the expensive cabling presently used to transfer the generated electricity to shore by simple piping, and the hydrogen would be stored in large, landside facilities.

Nov 06, 2014
Would lithium lined tanks keep so much hydrogen from leaking through the tank walls? Not as small as hydrogen atoms, but much smaller than iron atoms.

Graphene seems to be capable of stopping hydrogen leakage (it even stops helium from leaking)
http://phys.org/n...ble.html

It does not make sense to convert electricity to hydrogen then back unless efficiency is super high.

It makes sense even if efficiency is very low - because wind/hydro/solar will produce more energy than needed some of the time. Even if you're only 1% efficient in the cycle it's better than throwing that energy away (or having to keep coal powerplants running as backup).

Nov 06, 2014
This was done decades ago by Humboldt State in California. They used PV arrays to provide power for a remote aquarium, while also using the power to dissociate water, storing the hydrogen in a large tank. At night, the fuel cell (PEM), ran the systems on the excess hydrogen.

Nov 06, 2014
This is obsolete tech. It is much more effective to convert the oxygen in water to hydrogen and then to burn the resulting gas: http://www.solarh...nds.com/

Nov 06, 2014
Why would anyone burn Hydrogen when it can be turned directly to electricity in fuel cells?

And "converting the Oxygen to Hydrogen" is beyond your ability.

Nov 06, 2014
Oh, now this is brilliant. Be sure to store it at high pressure. Fact is the ability of hydrogen to store energy in its gaseous, pressurized state is extremely limited, even with a fuel cell. Better would be next generation lithium batteries. About 3 years. Until then, forget it.

Nov 06, 2014
I'm guessing because of all the difficulties with storing, transporting, using hydrogen it would be more realistic to use carbon dioxide and water and electricity to create methanol fuel like iceland does.
Look up Carbon Recycling International
The reality I suspect without some MAJOR breakthroughs neither one of these technology's are going to be a practical use for solar or wind. Nuclear and geothermal yes and hopefully soon.

Nov 06, 2014
Even if you're only 1% efficient in the cycle it's better than throwing that energy away (or having to keep coal powerplants running as backup).


Not really, because it would make the system prohibitively costly and reduce its EROEI to the point that the society wouldn't be able to sustain it, and itself at the same time.

Any technology that produces energy must also provide enough surplus to sustain the society that sustains the level of technology. If you're spending 90% of your energy gains back into making energy, you simply don't have the time and energy to keep up all the other stuff.


Nov 06, 2014
Not really, because it would make the system prohibitively costly and reduce its EROEI

From what I gather the system is dirt cheap. Fully closed and no moving parts - which means an almost indefinite lifetime. Even an -initially- very costly system with super low efficiency will eventually come out economically viable over time under that premise..

If you're spending 90% of your energy gains back into making energy, you simply don't have the time and energy to keep up all the other stuff.

It's for the EXCESS energy that would go unsued. Throwing away 90% of the EXCESS is perfectly fine (because currently we're throwing away 100%. 10% usage is better than 0% - get it?)
The year-round yield of renewables is very much plannable. The efficiency of storage systems is just the metric for how much excess (yearly) enegy production would be needed to shut down everything else.

Nov 07, 2014
Hydrogen extraction and compression require a lot of energy. H2 makes for an inefficient battery.

The better approach may be vanadium redox flow batteries. They seem to be coming to the grid at $300/kWh with 75% efficiency and a 20+ year lifespan. Deep storage means adding more non-pressurized tanks.

Nov 07, 2014
H2 makes for an inefficient battery.

There are other ways to store hydrogen (e.g. metal hydrides). And you could store a lot of hydrogen in something like the hollow towers that carry wind generators)

..and as noted: efficiency is not an issue if the decision is between doing nothing and at least having some storage.

Nov 07, 2014
H2 makes for an inefficient battery.

There are other ways to store hydrogen (e.g. metal hydrides). And you could store a lot of hydrogen in something like the hollow towers that carry wind generators)

..and as noted: efficiency is not an issue if the decision is between doing nothing and at least having some storage.


Yes, but we do have other storage options which are more efficient.

Nov 08, 2014
From what I gather the system is dirt cheap. Fully closed and no moving parts - which means an almost indefinite lifetime. Even an -initially- very costly system with super low efficiency will eventually come out economically viable over time under that premise..


No it won't, because it's causing a cost increase somewhere else by wasting energy.

If you need to build 100 times more windmills because your storage system wastes 99% of it, that really isn't economically, or ecologically sustainable in the least.

Even if your storage system has infinite lifetime so it represents virtually zero investment cost per unit of energy, having an efficiency of 50% would mean it increases the cost of any energy that flows through it by a factor of two simply by requiring twice as much input for any output.

That is, twice as many windmills, twice as many solar panels...


Nov 08, 2014
It's for the EXCESS energy that would go unsued.


There is no such thing as excess energy with renewable power, because it isn't producing enough energy as it is.

The "excess" is simply coming in at inconvenient times, and if you don't capture and use it, your system's capacity factor falls down and the energy that you do get becomes more expensive.

The capacity factor of a windmill for example, is 0.25 or 25% only because you utilize all the surges and peaks of production by force-feeding them into the grid. If you take a typical windmill with a Cp of 0.25 which represents the mean output, the median output is about 0.12 which is what you can expect on a typical day. Cutting off, or wasting the peaks into an inefficient storage medium, will move your actual production output closer to the median.


Nov 08, 2014
because currently we're throwing away 100%


No we aren't. We don't yet have enough renewables that we'd absolutely have to.

Currently all the excess is exported to neighboring grids - not wasted. They're calling it the "virtual battery", where the power is exported at a price below the minimum profit margin in order for the owners to keep collecting the feed-in tariffs from the government, and for keeping the production figures high.

In essence, the taxpayers are paying to give the surplus power away for free, or nearly free.

In smaller more isolated countries like the UK, there's occasinally the need to curtail wind power output as it stands, but generally it just isn't being done.

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