BY ANTHONY KING
Inspired by DNA, a US group has designed a chemical that can absorb the energy from sunlight and store it in a compact and rechargeable form. In molecular solar thermal (MOST) storage, a molecule captures light energy and bonds become strained like a mechanical spring to generate a higher-energy molecule.
‘When DNA is exposed to ultraviolet light, it can form what are called Dewar lesions,’ says Han Nguyen at UC Santa Barbara, California. ‘These contain significant ring strain and this stood out to us as a promising feature for energy storage.’
Heating consumes almost half of global energy demand, but almost two-thirds of the energy for heating homes, providing hot water and cooking comes from fossil fuels. This makes heating one of the largest sources of carbon emissions, yet stored solar energy offers a solution.
A simplified pyrimidine-based structure excited at 300nm was developed. Each molecule is capable of storing 228kJ/mol, which is equal to a gravimetric energy density of 1.6MJ/kg. This was shown at a milligram to hundred-milligram scale (Science, DOI: 10.1126/science.aec641). ‘We estimate that around 21kg of material would be needed to heat 63 gallons of cold water – roughly the amount of hot water an average household uses in a single day,’ says Nguyen.
The material is recharged and reused rather than consumed, so the same quality can keep working across multiple cycles. The team chose inexpensive, easy-to-manufacture materials.
‘The amount of energy stored in Han and coworkers’ Dewar pyrimidone is just a few times lower than the energy density of TNT. In contrast to energetic materials, however, this energy can be released controllably, in the presence of an acid,’ says Rafal Klajn, a chemist at the Institute of Science and Technology Australia.
This allows energy release on demand. ‘Adding a drop of an acid triggers a back-isomerisation reaction, releasing the energy accumulated in the metastable isomer. A lot of energy – nearly doubling the previous record for MOST energy storage capacity,’ says Klajn.
‘It is quite astonishing that these stunning properties are demonstrated in a molecule with as few as ten non-hydrogen atoms (C7H10N2O),’ Klajn adds.
A challenge now is device integration, says Nguyen: ‘We aim to incorporate MOST into existing infrastructure rather than build entirely new systems. We are developing recyclable heterogeneous catalysts to better control heat release and improve cyclability over many charge and discharge cycles.’
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