Economical renewable energy from water splitting gets big help from artificial intelligence

L to R, Professor Max Garcia-Melchor and PhD Candidate, Michael Craig, Trinity College Dublin.

Scientists from Trinity have taken a giant stride towards solving a riddle that would provide the world with entirely renewable, clean energy from which water would be the only waste product.

Reducing humanity’s carbon dioxide (CO2) emissions is arguably the greatest challenge facing 21stcentury civilisation – especially given the ever-increasing global population and the heightened energy demands that come with it.

One beacon of hope is the idea that we could use renewable electricity to split water (H2O) to produce energy-rich hydrogen (H2), which could then be stored and used in fuel cells. This is an especially interesting prospect in a situation where wind and solar energy sources produce electricity to split water, as this would allow us to store energy for use when those renewable sources are not available.

The essential problem, however, is that water is very stable and requires a great deal of energy to break up. A particularly major hurdle to clear is the energy or “overpotential” associated with the production of oxygen, which is the bottleneck reaction in splitting water to produce H2.

Although certain elements are effective at splitting water, such as Ruthenium or Iridium (two of the so-called noble metals of the periodic table), these are prohibitively expensive for commercialisation. Other, cheaper options tend to suffer in terms of their efficiency and/or their robustness. In fact, at present, nobody has discovered catalysts that are cost-effective, highly active and robust for significant periods of time.

So, how do you solve such a riddle? Stop before you imagine lab coats, glasses, beakers and funny smells; this work was done entirely through a computer.

By bringing together chemists and theoretical physicists, the Trinity team behind the latest breakthrough combined chemistry smarts with very powerful computers to find one of the “holy grails” of catalysis.

The team, led by Professor Max García-Melchor, made a crucial discovery when investigating molecules which produce oxygen: Science had been underestimating the activity of some of the more reactive catalysts and, as a result, the dreaded “overpotential” hurdle now seems easier to clear. Furthermore, in refining a long-accepted theoretical model used to predict the efficiency of water splitting catalysts, they have made it immeasurably easier for people (or super-computers) to search for the elusive “green bullet” catalyst.

Lead author, Michael Craig, Trinity, is excited to put this insight to use.

He said:

We know what we need to optimise now, so it is just a case of finding the right combinations.

The team aims to now use artificial intelligence to put a large number of earth-abundant metals and ligands (which glue them together to generate the catalysts) in a melting pot before assessing which of the near-infinite combinations yield the greatest promise.

In combination, what once looked like an empty canvas now looks more like a paint-by-numbers as the team has established fundamental principles for the design of ideal catalysts.

Professor Max García-Melchor added:

Given the increasingly pressing need to find green energy solutions it is no surprise that scientists have, for some time, been hunting for a magical catalyst that would allow us to split water electrochemically in a cost-effective, reliable way.

However, it is no exaggeration to say that before now such a hunt was akin to looking for a needle in a haystack.We are not over the finishing line yet, but we have significantly reduced the size of the haystack and we are convinced that artificial intelligence will help us hoover up plenty of the remaining hay.

This research is hugely exciting for a number of reasons and it would be incredible to play a role in making the world a more sustainable place. Additionally, this shows what can happen when researchers from different disciplines come together to apply their expertise to try to solve a problem that affects each and every one of us.

Professor Max García-Melchor is an Ussher Assistant Professor in Chemistry at Trinity and senior author on the landmark research that has just been published in a leading international journal, Nature Communications.

Learn more: Scientists take giant stride towards entirely renewable energy

 

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Nanoparticles convert carbon dioxide into methane using ultraviolet light for energy

Duke University researchers have engineered rhodium nanoparticles (blue) that can harness the energy in ultraviolet light and use it to catalyze the conversion of carbon dioxide to methane, a key building block for many types of fuels. Credit: Chad Scales

Illuminated rhodium nanoparticles catalyze key chemical reaction

Duke University researchers have developed tiny nanoparticles that help convert carbon dioxide into methane using only ultraviolet light as an energy source.

Having found a catalyst that can do this important chemistry using ultraviolet light, the team now hopes to develop a version that would run on natural sunlight, a potential boon to alternative energy.

Chemists have long sought an efficient, light-driven catalyst to power this reaction, which could help reduce the growing levels of carbon dioxide in our atmosphere by converting it into methane, a key building block for many types of fuels.

Not only are the rhodium nanoparticles made more efficient when illuminated by light, they have the advantage of strongly favoring the formation of methane rather than an equal mix of methane and undesirable side-products like carbon monoxide. This strong “selectivity” of the light-driven catalysis may also extend to other important chemical reactions, the researchers say.

“The fact that you can use light to influence a specific reaction pathway is very exciting,” said Jie Liu, the George B. Geller professor of chemistry at Duke University. “This discovery will really advance the understanding of catalysis.”

The paper appears online Feb. 23 in Nature Communications.

Despite being one of the rarest elements on Earth, rhodium plays a surprisingly important role in our everyday lives. Small amounts of the silvery grey metal are used to speed up or “catalyze” a number of key industrial processes, including those that make drugs, detergents and nitrogen fertilizer, and they even play a major role breaking down toxic pollutants in the catalytic converters of our cars.

Rhodium accelerates these reactions with an added boost of energy, which usually comes in the form of heat because it is easily produced and absorbed. However, high temperatures also cause problems, like shortened catalyst lifetimes and the unwanted synthesis of undesired products.

In the past two decades, scientists have explored new and useful ways that light can be used to add energy to bits of metal shrunk down to the nanoscale, a field called plasmonics.

“Effectively, plasmonic metal nanoparticles act like little antennas that absorb visible or ultraviolet light very efficiently and can do a number of things like generate strong electric fields,” said Henry Everitt, an adjunct professor of physics at Duke and senior research scientist at the Army’s Aviation and Missile RD&E Center at Redstone Arsenal, AL. “For the last few years there has been a recognition that this property might be applied to catalysis.”

Rhodium nanocubes observed under a transmission electron microscope. Credit: Xiao Zhang

Xiao Zhang, a graduate student in Jie Liu’s lab, synthesized rhodium nanocubes that were the optimal size for absorbing near-ultraviolet light. He then placed small amounts of the charcoal-colored nanoparticles into a reaction chamber and passed mixtures of carbon dioxide and hydrogen through the powdery material.

When Zhang heated the nanoparticles to 300 degrees Celsius, the reaction generated an equal mix of methane and carbon monoxide, a poisonous gas. When he turned off the heat and instead illuminated them with a high-powered ultraviolet LED lamp, Zhang was not only surprised to find that carbon dioxide and hydrogen reacted at room temperature, but that the reaction almost exclusively produced methane.

“We discovered that when we shine light on rhodium nanostructures, we can force the chemical reaction to go in one direction more than another,” Everitt said. “So we get to choose how the reaction goes with light in a way that we can’t do with heat.”

This selectivity — the ability to control the chemical reaction so that it generates the desired product with little or no side-products — is an important factor in determining the cost and feasibility of industrial-scale reactions, Zhang says.

“If the reaction has only 50 percent selectivity, then the cost will be double what it would be if the selectively is nearly 100 percent,” Zhang said. “And if the selectivity is very high, you can also save time and energy by not having to purify the product.”

Now the team plans to test whether their light-powered technique might drive other reactions that are currently catalyzed with heated rhodium metal. By tweaking the size of the rhodium nanoparticles, they also hope to develop a version of the catalyst that is powered by sunlight, creating a solar-powered reaction that could be integrated into renewable energy systems.

“Our discovery of the unique way light can efficiently, selectively influence catalysis came as a result of an on-going collaboration between experimentalists and theorists,” Liu said. “Professor Weitao Yang’s group in the Duke chemistry department provided critical theoretical insights that helped us understand what was happening. This sort of analysis can be applied to many important chemical reactions, and we have only just begun to explore this exciting new approach to catalysis.”

Learn more: LIGHT-DRIVEN REACTION CONVERTS CARBON DIOXIDE INTO FUEL

 

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Cobalt atoms on graphene a powerful combo for hydrogen production

Cobalt atoms shine in an electron microscope image of a new catalyst for hydrogen production. Courtesy of the Tour Group

Cobalt atoms shine in an electron microscope image of a new catalyst for hydrogen production. Courtesy of the Tour Group

Rice University catalyst holds promise for clean, inexpensive hydrogen production

Graphene doped with nitrogen and augmented with cobalt atoms has proven to be an effective, durable catalyst for the production of hydrogen from water, according to scientists at Rice University.

The Rice lab of chemist James Tour and colleagues at the Chinese Academy of Sciences, the University of Texas at San Antonio and the University of Houston have reported the development of a robust, solid-state catalyst that shows promise to replace expensive platinum for hydrogen generation.

Catalysts can split water into its constituent hydrogen and oxygen atoms, a process required for fuel cells. The latest discovery, detailed in Nature Communications, is a significant step toward lower-cost catalysts for energy production, according to the researchers.

“What’s unique about this paper is that we show not the use of metal particles, not the use of metal nanoparticles, but the use of atoms,” Tour said. “The particles doing this chemistry are as small as you can possibly get.”

Even particles on the nanoscale work only at the surface, he said. “There are so many atoms inside the nanoparticle that never do anything. But in our process the atoms driving catalysis have no metal atoms next to them. We’re getting away with very little cobalt to make a catalyst that nearly matches the best platinum catalysts.” In comparison tests, he said the new material nearly matched platinum’s efficiency to begin reacting at a low onset voltage, the amount of electricity it needs to begin separating water into hydrogen and oxygen.

The new catalyst is mixed as a solution and can be reduced to a paper-like material or used as a surface coating. Tour said single-atom catalysts have been realized in liquids, but rarely on a surface. “This way we can build electrodes out of it,” he said. “It should be easy to integrate into devices.”

The researchers discovered that heat-treating graphene oxide and small amounts of cobalt salts in a gaseous environment forced individual cobalt atoms to bind to the material.

Electron microscope images showed cobalt atoms widely dispersed throughout the samples.

They tested nitrogen-doped graphene on its own and found it lacked the ability to kick the catalytic process into gear. But adding cobalt in very small amounts significantly increased its ability to split acidic or basic water.

Read more: Cobalt atoms on graphene a powerful combo

 

 

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Discovery of a highly efficient catalyst eases way to hydrogen economy

Bathed in simulated sunlight, this photoelectrolysis cell in the lab of Song Jin splits water into hydrogen and oxygen using a catalyst made of the abundant elements cobalt, phosphorus and sulfur. Photos: David Tenenbaum

Bathed in simulated sunlight, this photoelectrolysis cell in the lab of Song Jin splits water into hydrogen and oxygen using a catalyst made of the abundant elements cobalt, phosphorus and sulfur.
Photos: David Tenenbaum

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 noble metals 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.

“If you want to make a dent in the global warming problem, you have to think big.”

Song Jin

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.”

Read more: Discovery of a highly efficient catalyst eases way to hydrogen economy

 

 

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Laser-burned graphene gains metallic powers

Rice University chemists embedded metallic nanoparticles into laser-induced graphene. The particles turn the material into a useful catalyst for fuel cell and other applications. Courtesy of the Tour Group

Rice University chemists embedded metallic nanoparticles into laser-induced graphene. The particles turn the material into a useful catalyst for fuel cell and other applications. Courtesy of the Tour Group

Rice University scientists find possible replacement for platinum as catalyst

Rice University chemists who developed a unique form of graphene have found a way to embed metallic nanoparticles that turn the material into a useful catalyst for fuel cells and other applications.

Laser-induced graphene, created by the Rice lab of chemist James Tour last year, is a flexible film with a surface of porous graphene made by exposing a common plastic known as polyimide to a commercial laser-scribing beam. The researchers have now found a way to enhance the product with reactive metals.

The research appears this month in the American Chemical Society journal ACS Nano.

With the discovery, the material that the researchers call “metal oxide-laser induced graphene” (MO-LIG) becomes a new candidate to replace expensive metals like platinum in catalytic fuel-cell applications in which oxygen and hydrogen are converted to water and electricity.

“The wonderful thing about this process is that we can use commercial polymers, with simple inexpensive metal salts added,” Tour said. “We then subject them to the commercial laser scriber, which generates metal nanoparticles embedded in graphene. So much of the chemistry is done by the laser, which generates graphene in the open air at room temperature.

A scanning electron microscope image shows cobalt-infused metal oxide-laser induced graphene.

“These composites, which have less than 1 percent metal, respond as ‘super catalysts’ for fuel-cell applications. Other methods to do this take far more steps and require expensive metals and expensive carbon precursors.”

Initially, the researchers made laser-induced graphene with commercially available polyimide sheets. Later, they infused liquid polyimide with boron to produce laser-induced graphene with a greatly increased capacity to store an electrical charge, which made it an effective supercapacitor.

 

 

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