Tiny Materials Could Lead To Big Energy Savings

The tree outside the window has a lot to teach us about clean energy production.

“Plants have perfected the synthesis of oxygen through photosynthesis,” explained Ivan Moreno-Hernandez, assistant professor of Chemistry.

In photosynthesis, plants use the energy of the sun to split water molecules into oxygen and hydrogen. The hydrogen atoms are used to create the chemical energy the plants need to grow, while oxygen is a clean, and welcome, by-product.

While plants are great at these electrochemical reactions — harnessing energy by moving electrons around through chemical interactions — humans still have a long way to go to catch up. Figuring out how to mimic the success of photosynthesis could open the door to clean energy technologies that are less expensive and more efficient than those we currently have. 

Moreno-Hernandez’s research group develops nanomaterials — substances so small they can only be viewed through high-powered microscopes — that act as catalysts, chemical middlemen that make it easier for these reactions to take place.

In a paper his research group recently published in the Journal of the American Chemical Society (JACS), Moreno-Hernandez addresses a stumbling block in current research: the cost and availability of materials that are currently used as catalysts, such as the element iridium.

“A lot of the work we do focuses on the challenge of identifying catalysts that are scalable, inexpensive and active to extract oxygen from water,” Moreno-Hernandez said. One approach the group uses to identify potential new catalysts is liquid-phase electron microscopy (LPEM). “This is a new technique that allows you to watch chemical reactions in water in real time at atomic resolution. You can see individual atoms and how they change over time, allowing us to understand how materials degrade or activate.”

Moreno-Hernandez uses what he learns from LPEM to design new nanomaterials that are better catalysts than iridium oxide or that use iridium more efficiently, thereby saving money. For example, his team has designed catalysts that are durable enough to last for thousands of hours. They have also developed a new class of materials consisting of extremely thin layers of expensive materials (like iridium) that have cores composed of much more inexpensive materials — not unlike plated jewelry.

“It's actually a really good way to use the metals,” Moreno-Hernandez said, “because typically when you make a particle out of the metal oxide, only the surface is seeing the reaction and the middle is not doing anything. We've figured out the chemistry to replace that middle with an inexpensive metal so it doesn't have to be pure iridium all the way through.”

In one experiment, Moreno-Hernandez and his researchers put layers of costly ruthenium oxide on the surface of titanium dioxide — the active ingredient in sunscreens. “Essentially, we take the same particles that are used in sunscreen and coat them with small amounts of a noble metal oxide,” he said. “It turns out that those materials are even more active than the pure material, they're much cheaper and easier to get, and they last a long time.”

Having access to LPEM technology is integral to Moreno-Hernandez’s research, and the microscopy resources at Duke and in the area are excellent. “Duke is definitely the best place in the world to do the kind of science I'm doing,” he said. “Whenever I need something — or my students need something —we can always find it at Duke or in the Research Triangle. That's just been incredible for making progress in this field.”

Moreno-Hernandez’s research group, like most in the Chemistry department, includes not only graduate and postdoctoral students, but undergraduates as well. The undergraduates are not only granted full access to the research, they’re significantly contributing to it.

“One of the undergraduates who joined my lab about a year ago is already an author on a manuscript. He learned how to do electron microscopy, which is incredibly challenging. He has gained expertise in nanomaterial synthesis and is now working on his own project developing a new catalyst.”

Basic research — fundamental science — is Moreno-Hernandez’s main focus. Commercializing materials happens further down the line, with the discoveries made today hopefully leading to better sources of renewable energy and less dependence on fossil fuels in the future.

Many nanomaterials that are discovered will not lead to a product, but Moreno-Hernandez acknowledges that there are some that do make it. “I am working with the Duke Patent Office on many of these materials,” he said, “and that’s an ongoing process.”