New material could store solar energy for months or even years

China Energy Storage Network: If humans want to do better in utilizing renewable energy, scientists must work harder to find effective ways to store energy. According to the latest issue of Materials Chemistry, British scientists have identified a special material that can store solar energy for months or even years - a metal organic framework (MOF) material.

The material functions a bit like the phase-change materials used in hand warmers, according to researchers at Lancaster University in the UK. But the benefit of MOFs is that they can capture free energy directly from the sun.

In MOFs, carbon-based molecules form structures by linking metal ions. Crucially, MOFs are porous so they can form composites with other small molecules. By adding molecules of azobenzene, a light-absorbing compound, the resulting composite can store absorbed UV energy at room temperature for at least four months before releasing it. This is a major breakthrough over the days or weeks of energy storage achieved by most current light-responsive materials.

Azobenzene acts as a photoswitch - a molecular machine that responds to external stimuli such as light or heat. Under the influence of ultraviolet light, the molecule changes shape while staying within the framework of the MOF pores, effectively storing energy.

The researchers said that while past research has also focused on storing solar energy in photoelectric switches, it usually requires it to be kept in a liquid. Switching to a MOF composite solid means that the system is easier to assemble and has higher chemical stability. The material has no moving or electronic parts, so there is no loss in storing and releasing solar energy.

The researchers say that while the material still needs some improvements to make it commercially viable, it could eventually be used to de-ice car windshields or provide additional heat in homes and offices. Photoelectric switches like this also have potential applications in data storage and drug delivery. As the technology develops further, it is expected that other materials can be created that can store more energy, providing another cost-effective and reliable way to store energy.

(Originally published on December 18, Science and Technology Daily, page 2)