Fundamental research carried out by faculty like Jie Liu, George Barth Geller Distinguished Professor of Chemistry, provides the necessary background for developing new clean-energy technologies. (John West/Trinity Communications)
Harnessing Solar Energy to Deliver Hydrogen Where It’s Most Needed
It’s expensive to transport a gas, especially hydrogen.
Solids and liquids can be moved from one place to another efficiently using infrastructure like trucks, trains and ships, but gases are a different story. In order to transport a gas like hydrogen — an important component of both fertilizer and fuels — in a safe and cost-effective way, it needs to be converted to a liquid state. It’s even better if you don’t have to transport it at all, instead synthesizing it cheaply and easily where it’s needed.
This is the focus of Jie Liu’s research. Boosted by a Duke Science and Technology Launch Seed Grant, Liu, George Barth Geller Distinguished Professor of Chemistry, and his research team have been trying to create a cost-effective way to use solar energy to synthesize methane (CH4) or ammonia (NH3) as hydrogen carriers, allowing hydrogen to be stored in a form that can be used in carbon-neutral fuel technologies.
“What I'm trying to do,” Liu said, “is change hydrogen into something that can be moved from where it is produced to where it is needed more economically.”
“Green” methane
Methane — CH4 — is essentially natural gas. Traditional technology extracts natural gas from the ground, expending energy — often in the form of polluting, non-renewable fuels — in the process.
“Green” methane can be created chemically using a solar powered catalyst, a chemical middleman that helps carbon and hydrogen atoms combine into a methane molecule. There are advantages to producing methane in this way. Although it’s still a greenhouse gas, “green” methane is renewable, and its synthesis has smaller environmental impacts than extracting natural gas from the ground. It all depends on developing efficient and cost-effective ways of making it.
“The net emission to synthetize green methane is zero when the carbon dioxide is captured from the environment. If you get more methane from underground, you produce more carbon dioxide, which would increase the total concentration of carbon dioxide in the environment,” Liu said.
Synthesizing ammonia with solar energy
Another possibility for storing and transporting hydrogen is to react it with nitrogen to make ammonia, “a chemical that we use a lot in agriculture for fertilizer, as well as in many other industries,” Liu said. His research group has a paper currently under review that outlines how to improve the efficiency of converting hydrogen and nitrogen into ammonia using sunlight as the power source.
In addition to its use as a fertilizer, ammonia is another cost-effective hydrogen carrier. There is existing infrastructure for transporting ammonia, Liu said, whereas if you try to transport hydrogen gas in a truck, the energy you consume is greater than the amount of energy that hydrogen load would yield.
Opening doors to new markets
But what if you didn’t have to transport hydrogen at all?
Liu teamed up with undergraduates in the Design Climate class, a collaboration between the Nicholas School of the Environment and the Pratt School of Engineering, to consider possibilities for making ammonia in situ, where it is needed.
“In many countries,” Liu said, “people don't have access to ammonia for fertilizer. They have to import it, which can be prohibitively expensive. If you can extract hydrogen from water using solar energy and get nitrogen from air, then you can generate ammonia locally using my process, because it runs on solar light.”
While Liu provided the scientific component of the Design Climate project, an advisor from industry helped the students consider cost and other business factors. Together, they tried to determine if it’s possible to start a company that will manufacture ammonia in areas where inexpensive, readily available fertilizer could be a game-changer for local farmers.
Eesha Yaqub, who graduated from Duke in May with a degree in Environmental Sciences, was excited to participate in the project. “I wanted to join this Design Climate team because a lot of my focus at Duke has been energy related,” she said. “I really enjoyed learning about hydrogen and ammonia technology, and I wanted to explore the feasibility of a reactor that can produce multiple clean fuels from hydrogen.
“Jie Liu has been a great co-designer and a great source of guidance for our team,” Yaqub added. “I genuinely believe this can scale up, because the efficiency numbers regarding producing ammonia have been very good.”
Liu stresses that his work is fundamental research that provides the necessary background for developing new clean-energy technologies. “We haven't set up any big reactor yet, but this research has implications for future applications to be able to run on an energy source that will have a much smaller CO2 footprint,” he said. “My interest is to reduce the total emission of carbon dioxide in our energy applications.”
Liu underscored the importance of moving forward with this research as quickly as possible. “You know, it's almost too late if we don't act. I'll do my part, and I hope the general public will realize the importance of this kind of research so we’ll be able to stop using fossil fuels as a source of energy.”
