Sign into your Physics World account to get access to all available digital issues of the monthly magazine. Your Physics World account is separate to any IOP accounts you may have
Create a Physics World account to get access to all available digital issues of the monthly magazine. Your Physics World account is separate to any IOP accounts you may have.
Note: The verification e-mail to complete your account registration should arrive immediately. However, in some cases it takes longer. Don’t forget to check your spam folder.
If you haven’t received the e-mail in 24 hours, please contact customerservices@ioppublishing.org.
Please enter the e-mail address you used to register to reset your password
Note: The verification e-mail to change your password should arrive immediately. However, in some cases it takes longer. Don’t forget to check your spam folder.
If you haven’t received the e-mail in 24 hours, please contact customerservices@ioppublishing.org
Thank you for registering with Physics World
If you’d like to change your details at any time, please visit My account
Being able to store renewable energy, such as that produced by sunlight, so that it can be used at night or on cloudy days remains a major challenge. In recent years, researchers have been looking into molecular solar thermal (MOST) energy storage systems that harness the energy from photons and release it when needed. Now, a joint US team from Grace Han’s lab at the University of California, Santa Barbara, and Kendall Houk’s lab at the University of California, Los Angeles, has published details of a bio-inspired pyrimidone-based molecule that, when highly strained, stores a record amount of photon energy in its chemical bonds. The energy released when the molecule is allowed to relax is enough to boil water, the researchers say.
The structure of pyrimidone looks very much like that of a component found in DNA, which, when exposed to ultraviolet light, can reversibly form “Dewar lesions”. “These lesions naturally contain significant ring strain, something that immediately stood out to us as a promising feature for energy storage,” says first author Han Nguyen.
The researchers set out to engineer a synthetic version of this structure, the Dewar isomer of pyrimidone, which they also designed to be highly strained. They did this by combining a de-aromatization strategy with a compounded strain effect from fusing two already strained rings contained within the molecule.
“As a result, each molecule can store a large amount of energy, reaching 228 kJ/mol,” says Nguyen. “This translates to a gravimetric energy density of 1.6 MJ/kg, a value that is at least 1.6 times higher than previous MOST energy storage systems and nearly double the energy density of a standard lithium-ion battery (around 0.9 MJ/kg).”
The system can be described as a mechanical spring, she says. “When hit with sunlight, it twists into a strained, high-energy shape. It stays locked in that shape until a trigger – such as a small amount of heat or a catalyst – snaps it back to its relaxed state, releasing the stored energy as heat. It can be thought of as a liquid solar battery that stores sunlight and can be recharged.”
The result, Nguyen explains, addresses a long-standing limitation of MOST materials: insufficient energy density for practical use. Until now, the stored heat could only be released and used in well-insulated environments to minimize losses. “In contrast, our system releases enough heat to operate under ambient conditions and in our demonstrations, the heat output is strong enough to boil a sample of 0.5 mL of water in under one second.”
According to the researchers, the study “marks an important step toward real-world applications and shows that MOST systems can now move beyond controlled laboratory settings and function robustly in practical environments”.
This pyrimidone system had not been explored before as a candidate for MOST materials, so the researchers first had to design a simplified structure based on the Dewar lesion. The challenge, remembers Nguyen, was to strip away parts that were not relevant to the application in hand while retaining the features responsible for efficient storage and release of energy. “Through iterative design and testing, we arrived at a structure that is both efficient and practical,” she says.
Another challenge was improving functionality. “Our early designs still required solvents, which limit practical use,” she explains. “To solve this, we engineered the system into a liquid-state molecule that can operate without solvent.”
The fact that the material is soluble in water means that it could be pumped through roof-mounted solar collectors to charge during the day and stored in tanks to provide heat at night, adds team member Benjamin Baker. “With solar panels, you need an additional battery system to store the energy, but with molecular solar thermal energy storage, the material itself is able to store that energy from sunlight.”
The UCSB researchers hope their work, which they detail in Science, will encourage further research in the field, so that pyrimidone and other heterocycles like it can be further improved and optimized. “We would like to design and develop molecules that absorb in a broader range of solar radiation,” says Houk. “We also want to maintain high energy density, thermal stability and energy release upon thermal ring opening and will use quantum mechanical calculations to make these predictions.”
Freeze–thaw battery could help store solar and wind energy
To this end, he adds, the team plans to screen hundreds to thousands of molecules, perhaps with AI assistance, to open up new avenues for experimental research.
Nguyen tells Physics World that the goal of her laboratory is “to make heat more affordable and accessible, especially in situations where people need it most. For example, our materials could be useful in emergency or disaster settings where access to power and fuel is limited”.
Looking further ahead, she says that the technology could be integrated into real-world systems, such as heating for houses and buildings, helping to provide more reliable and accessible heat in everyday life.
Note: The verification e-mail to complete your account registration should arrive immediately. However, in some cases it takes longer. Don’t forget to check your spam folder.
If you haven’t received the e-mail in 24 hours, please contact customerservices@ioppublishing.org.
Quick reads for curious minds and busy people. Explore leading science in minutes.
Physics World represents a key part of IOP Publishing’s mission to communicate world-class research and innovation to the widest possible audience. The website forms part of the Physics World portfolio, a collection of online, digital and print information services for the global scientific community.

source