If you want to use multiple methods to generate electricity, such as waste heat and movement, for example, you normally have to use independent mechanisms and combine the results. Now researchers from the University of Oulu in Finland have discovered a crystal mineral material that is able to simultaneously generate energy from light, heat, and mechanical force, opening up a whole new range of possibilities for multi-source electricity-generating devices.
The material used by the researchers is a perovskite material, a group of minerals that have the same type of crystal structure as that of the naturally-occurring mineral calcium titanate (CaTiO3) and are known for their various abilities to help boost the conversion of sunlight to power in solar cells and even assist in creating hyperefficient light-emitting crystals.
Different types of perovskites have the ability to harness different types of energy. When a certain type of perovskite solar cell is exposed to light, for example, photons of light cause electrons in the crystal to jump across an "energy gap" and create an electric current. A similar effect occurs when thermal energy, or heat, is applied to a different type where the excitation of electrons causes an electric current to flow, known as the pyroelectric effect.
Deforming the material also generates a current as the crystalline atomic structure flexes in perovskites in response to external stimuli, causing the magnetic dipoles of the electrons in the structure to be forced out of alignment, thereby inducing an electric current due to what is known as the piezoelectric effect.
The material used by the University of Oulu team is capable of producing an electric current from all three of these types of energy.
The type of perovskite in question is created from what is known as KBNNO, which is formed when KNbO3 nanocrystals are modified with the addition of quantities of barium and nickel. Previous studies have only concentrated on the photovoltaic and magnetic properties of KBNNO at temperatures hundreds of degrees below freezing, and without testing the effects of pressure or temperature. According to the researchers, their work is the first time that a complete range of pressure, heat, magnetic, and light effects on KBNNO has evaluated all of these properties at the same time above room temperature.
The researchers claim that their initial experiments indicate that KBNNO is quite adept at generating electric current from light, but it isn't so good as other perovskites at doing so with heat and pressure. But they are confident that altering the balance of elements in KBNNO will vastly improve its piezoelectric and pyroelectric capabilities.
"It is possible that all these properties can be tuned to a maximum point," says Dr Yang Bai from the University of Oulu, who is aiming to have a prototype multi-energy device built within the next year. "This will push the development of the Internet of Things and smart cities, where power-consuming sensors and devices can be energy sustainable."
Exploring the potential improvements that addition of sodium would bring to the mix, the researchers hope to eventually commercialize their discovery, noting that its production is a straightforward and scalable process. The researchers also believe that this type of material could eventually be used in mobile devices to supplement batteries to improve energy efficiency and reduce recharge cycles, or, one day, create multi-energy harvesting units that may even make batteries for small devices obsolete.
The full paper detailing this discovery can be found in the journal Applied Physics Letters.
Source: American Institute of Physics
