Discovery of a highly efficient catalyst eases way to hydrogen economy

September 14, 2015 by David Tenenbaum
Bathed in simulated sunlight, this photoelectrolysis cell in the lab of Song Jin, a professor of chemistry at the University of Wisconsin-Madison, splits water into hydrogen and oxygen using a catalyst made of the abundant elements cobalt, phosphorus and sulfur. Credit: David Tenenbaum/University of Wisconsin-Madison

Hydrogen could be the ideal fuel: Whether used to make electricity in a fuel cell or burned to make heat, the only byproduct is water; there is no climate-altering carbon dioxide.

Like gasoline, hydrogen could also be used to store energy.

Hydrogen is usually produced by separating water with electrical power. And although the water supply is essentially limitless, a major roadblock to a future "hydrogen economy" is the need for platinum or other expensive in the water-splitting devices.

Noble metals resist oxidation and include many of the precious metals, such as platinum, palladium, iridium and gold.

"In the hydrogen evolution reaction, the whole game is coming up with inexpensive alternatives to platinum and the other noble metals," says Song Jin, a professor of chemistry at the University of Wisconsin-Madison.

In the online edition of Nature Materials that appears today, Jin's research team reports a hydrogen-making catalyst containing phosphorus and sulfur—both common elements—and cobalt, a metal that is 1,000 times cheaper than platinum.

Catalysts reduce the energy needed to start a chemical reaction. The new catalyst is almost as efficient as platinum and likely shows the highest catalytic performance among the non-noble metal catalysts reported so far, Jin reports.

The advance emerges from a long line of research in Jin's lab that has focused on the use of iron pyrite (fool's gold) and other inexpensive, abundant materials for energy transformation. Jin and his students Miguel Cabán-Acevedo and Michael Stone discovered the new high-performance catalyst by replacing iron to make cobalt pyrite, and then added phosphorus.

Although electricity is the usual energy source for splitting water into hydrogen and oxygen, "there is a lot of interest in using sunlight to split water directly," Jin says.

The new catalyst can also work with the energy from sunlight, Jin says. "We have demonstrated a proof-of-concept device for using this cobalt catalyst and solar energy to drive hydrogen generation, which also has the best reported efficiency for systems that rely only on inexpensive catalysts and materials to convert directly from sunlight to hydrogen."

Many researchers are looking to find a cheaper replacement for platinum, Jin says. "Because this new catalyst is so much better and so close to the performance of platinum, we immediately asked WARF (the Wisconsin Alumni Research Foundation) to file a provisional patent, which they did in just two weeks."

Many questions remain about a catalyst that has only been tested in the lab, Jin says. "One needs to consider the cost of the catalyst compared to the whole system. There's always a tradeoff: If you want to build the best electrolyzer, you still want to use platinum. If you are able to sacrifice a bit of performance and are more concerned about the cost and scalability, you may use this new cobalt ."

Strategies to replace a significant portion of fossil fuels with renewable solar energy must be carried out on a huge scale if they are to affect the climate crisis, Jin says. "If you want to make a dent in the global warming problem, you have to think big. Whether we imagine making hydrogen from electricity, or directly from sunlight, we need square miles of devices to evolve that much . And there might not be enough to do that."

Explore further: Why platinum nanoparticles become less effective catalysts at small sizes

More information: Efficient hydrogen evolution catalysis using ternary pyrite-type cobalt phosphosulphide, DOI: 10.1038/nmat4410

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Urgelt
not rated yet Sep 21, 2015
Bah. Grumble grumble humbug.

Look, guys, using electricity to separate oxygen and hydrogen from water molecules is just a different kind of battery. Electricity goes in, fuel comes out, recombine the fuel to recover the electricity.

Only it's way less efficient than chemical batteries. It's 'lossy.' A lot of the electricity going into this system doesn't come back out as electrical power.

It has three other flaws:

1. Uncompressed hydrogen is useless for vehicular power. It has to be compressed if you want to move vehicles around with it. Compressing uses up a lot of power and is the primary reason that storing electricity as molecular hydrogen is 'lossy.'

2. The energy density of compressed hydrogen is fixed to the power you invest in compressing it, with upper limits set by the storage container.

3. Hydrogen is devilishly difficult to store. It leaks from any container. More, it leaks more aggressively the higher the pressure in the container.
Urgelt
not rated yet Sep 21, 2015
Furthermore, the infrastructure required to treat hydrogen as we now treat gasoline is going to cost uncountable trillions of dollars, while the fuel itself will never be cost competitive with battery-powered vehicles due to losses at every step in producing, compressing, distributing and consuming energy.

By contrast, the power grid already exists. It may need tweaks, but the level of investment to support battery-powered vehicles is trivial next to the cost of a hydrogen infrastructure.

The only drawbacks to batteries powering vehicles are energy density, cost and recharging time. But batteries have improved, and they will improve a lot more in coming years.

Whereas efficiency gains in compression and storage for hydrogen aren't even theoretically possible. All of the tweaking is at the molecular disassociation stage; there are no innovations in sight for higher-efficiency compression or lossless storage.

We are not closer to a hydrogen infrastructure.
antialias_physorg
not rated yet Sep 21, 2015
Only it's way less efficient than chemical batteries. It's 'lossy.' A lot of the electricity going into this system doesn't come back out as electrical power.

That's not the point. The point is that hydrogen is storeable. Since it's created with free energy (i.e. energy you would otherwise have to dump because it cannot be used immediately it's completely irrelevant that it's lossy. It could be 0.0001% efficient and it would still be well worth it.)

(And BTW: ALL forms of energy carriers are lossy conversions. None more so than coal, oil or gas. The efficiency that went into turning solar power into coal or oil is atrocious)

Hydrogen is devilishly difficult to store. It leaks from any container.

A layer of graphene seems to be able to make containers helium tight (which is harder than making it hydrogen tight). With hydrogen stored in bound form (e.g. metal hydrides) there's no leakage at all.
Urgelt
not rated yet Sep 21, 2015
Well, Auntie, we'll have to agree to disagree on this one.

Atomic helium is harder to store than molecular hydrogen, but that doesn't make hydrogen easy to contain as a gas. You can cool it to a liquid to get around the container problem; but that takes a *lot* of energy. As a gas, this stuff leaks.

Maintaining hydrogen pipelines will be a nightmare.

Producing graphene for commercial applications is still problematic and horribly expensive. That technology may arrive at some point, granted.

But compressing to usable densities is still a great huge energy cost. The losses you take with charging and discharging batteries are insignificant compared to that.

Energy you would otherwise dump if not used immediately can be stored in batteries - or water pumped to a higher elevation, or heating sodium, or any number of other schemes - as readily as storing it as compressed hydrogen gas. Almost any other solution is less 'lossy' because they avoid compression losses.
MR166
not rated yet Sep 24, 2015
Actually the compression losses could be the least of the problems. Transportation is a huge problem. Steel pipelines, I don't think so because hydrogen embrittlement is a huge problem. Cryogenic storage and transportation is very lossy. Thus, more than likely, H2 has to be created and stored on site for transportation or storage use. At this point in time batteries look to be a more reasonable storage medium than transported H2.

If battery development stalls H2 production, storage and conversion back into electrical power at a central site could be a viable solution to the intermittent nature of wind and solar.

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