The intensity of natural resources that offer renewable energy varies every day and also with seasons. Spring blows high winds to scour the deserts and fills rivers with snowmelt. Summer has long sunlit hours, and as the fall transitions into winter, the days tend to shorten.
Multiple options are required to store renewable energy that matches how it is stored, from batteries to fuel cells. Batteries exhibit reliable storage for a shorter duration, in the range of hours to days.
Among all the various storage methods for storing renewable energy, there is one unique way that enables energy storage for months at a time. Storing energy in the chemical bonds of molecules like hydrogen is one such method.
Scientists at the Pacific Northwest National Laboratory (PNNL) have performed decades of basic research to contribute extensive information regarding the role of catalysts in converting energy into molecular bonds, and storing the energy by creating bonds and discharging it by breaking bonds.
Currently, a research team guided by chemist and Laboratory Fellow Tom Autrey is focused on converting chemical energy storage into practical setups that could potentially power neighborhoods, industry and infrastructures, for which the team is analyzing entire systems, right from catalyst to reactors to end products.
Our work considers everything from electrons to dollars.
Mark Bowden, Chemist, Pacific Northwest National Laboratory
Bowden is a long-time contributor to the project. The interdisciplinary group unites knowledge in engineering, chemistry, techno economics and theoretical calculations to evaluate the practical viability of chemical energy storage systems for large-scale storage.
The researchers will be a supportive home at the Energy Science Center in PNNL, bound to open later this year. The center will accommodate more than 250 staff members and a chamber of advanced scientific instruments distributed earlier at different places around the campus. This will create a collaborative environment for the team to build on its long history of progress.
Furthermore, the research at the Energy Sciences Center will include work focusing on creating new catalysts for converting electricity into chemical bonds via the Center for Molecular Electrocatalysis.
Hydrogen as the Starting Point
According to Autrey, a discussion regarding chemical storage usually revolves around hydrogen as the most potent molecule. It can be made by splitting water into hydrogen and oxygen gases before using it for a carbon-free energy source. In a fuel cell, hydrogen fuses with oxygen to generate water and electricity.
Yet, the storage of pure hydrogen as a liquid or gas is logistically challenging as it requires either large, high-pressure tanks or very low temperatures. Also, researchers are developing several other alternative storage solutions to store hydrogen in materials or molecules.
The researchers at PNNL are working to develop a hydrogen carrier system that could harness chemical reactions, enabling the addition and removal of hydrogen from stable molecules on demand. There is a whole subfield of chemistry that studies the catalysts capable of performing hydrogen addition and removal.
Scientists at PNNL are experts in designing catalysts that can store hydrogen in molecules like methylcyclohexane, formic acid and butanediol, among others.
Ba Tran, a chemist from PNNL, was involved in assessing the suitability of hydrogen-rich ethanol, integrated with an established catalyst, to cycle with ethyl acetate for prolonged storage. Hydrogen stays bonded to the ethanol until it can be discharged for utilization and the ethanol converted into ethyl acetate.
The catalyst is capable of adding two molecules of hydrogen to one ethyl acetate molecule, thereby generating two stable ethanol molecules that tend to store the hydrogens.
Analysis Beyond the Lab
Apart from gaining better insights into the basic chemistry of adding and releasing hydrogen from other molecules, Tran and his collaborators combined data from experimental measurements and advanced molecular simulations into studies of larger-scale systems.
We want to see how the process of storing hydrogen in ethanol—and other forms of chemical energy storage — would behave in an application-scale system.
Samantha Johnson, Theoretical Chemist, Pacific Northwest National Laboratory
In the ethanol research, for instance, the team examined a reactor design at a range applicable for seasonal energy storage in a neighborhood. The chemistry of the reactions performed better and the project explained the team useful lessons regarding the engineering required for a practical system, thereby leading them in new ways to explore various hydrogen carriers.
Grounding Research in Reality
While analyzing the molecular details of the functioning of hydrogenation catalyst or designing a neighborhood scale storage system, the scientists were constantly posing questions that would possibly take the research from the lab into the real world. The researchers made a cyclical method to problem-solving, where various parts of their research interact with one another and provide a more complete picture of the working of energy storage.
Uniting researchers with different technical backgrounds enables the team to find resolvable issues or difficulties for the wider energy storage field.
The collaborative environment and more instrumentation of the new Energy Sciences Center suit the team’s operation. The project is a part of a vast range of energy-related research at PNNL which could be expedited with the establishment of new buildings. The Energy Sciences Center unites scientists with different expertise to promote collaboration.
We want to help move our society towards a future-focused on renewable energy.
Tom Autrey, Chemist and Laboratory Fellow, Pacific Northwest National Laboratory
The team acknowledges financial support from the Hydrogen and Fuel Cell Technologies Office of the Office of Energy Efficiency and Renewable Energy, through the Hydrogen Advanced Research Consortium (HyMARC), established as part of the U.S. Department of Energy’s Energy Materials Network.
Storing Energy in Chemical Bonds
Video Credit: Animation by Sara Levine | Pacific Northwest National Laboratory.