Researchers at Lancaster University have developed a new material that can store energy for months, and potentially years, at a time. The material can be activated by light, and then release the pent-up energy on demand in the form of heat.The team started with a metal-organic framework (MOF), materials that are famous for being very porous and as such, having an extremely high surface area. That in turn allows them to hold onto large amounts of molecules, making them great for desalinating or filtering water, capturing carbon dioxide out of the air, or delivering drugs in the body.
For the new study, the Lancaster researchers tested out how well a MOF might be able to store energy. They started with a version of the material called a DMOF1, and loaded its pores with azobenzene molecules. This compound is excellent at absorbing light, which causes its molecules to physically change shape.
When the material is exposed to UV light, the azobenzene molecules bend into a strained shape, and normally they would bounce back as soon as the light is turned off. But in this case, the tiny MOF pores keep them jammed in that shape, storing their potential energy in a similar manner to a compressed spring.
When it’s time to reclaim that energy, the material is warmed up a little. At that point, it quickly releases its stored energy as a burst of heat. Importantly, the released heat is much higher than the “trigger” heat, so it is a net gain.
Because it’s a mechanical effect, it requires no external power to store the energy, and it can be done at room temperature for long periods of time. In the study, the energy storage lasted for the entire four-month experiment period, and the researchers estimate that it should have an energy storage shelf life of up to 4.5 years.
“The material functions a bit like phase change materials, which are used to supply heat in hand warmers,” says John Griffin, joint Principal Investigator of the study. “However, while hand warmers need to be heated in order to recharge them, the nice thing about this material is that it captures ‘free’ energy directly from the Sun. It also has no moving or electronic parts and so there are no losses involved in the storage and release of the solar energy. We hope that with further development we will be able to make other materials which store even more energy.”
In its current form, the team says the material has a rather low energy density, but future work will focus on improving that. Eventually, the material could be used to capture energy from the Sun during the day to release heat at night, or store summer energy for winter use. It might make for a useful coating to help heat buildings, or to quickly de-ice windows and windshields on cold winter mornings.
The research was published in the journal Chemistry of Materials.