Many forms of energy surrounds us every day and most of it is not being put to good use. Your own movements, sunlight and the heat in a room are all energy sources that could potentially power wearable and portable gadgets, ranging from smart watches to biometric sensors.
A research team from the University of Oulu in Finland have discovered a specific mineral having a perovskite crystal structure that has the properties required to extract energy from numerous sources simultaneously.
Perovskites are a family of minerals. Many of these show potential for collecting one or two types of energy at a time, but not simultaneously. While one family member might be good for harnessing energy from changes in pressure and temperature, another might have the right properties for converting solar energy into electricity efficiently. The latter would typically be used in solar cells. A perovskite that can convert changes in pressure arising from motion is known as piezoelectric material, while those that are able to convert temperature produced by movement are called pyroelectric.
Sometimes however, more than one type of energy is not enough. A specific form of energy might not always be available. It could be a cloudy day, or you might be in a situation where movement is not practical or even possible, for example you being in a meeting. Devices that can harness multiple forms of energy have been developed by other researchers, but these require multiple materials. This adds bulk to the device and defeats the objective of making them as small and portable as possible.
In some ferroelectric materials such as KBNNO, the dipoles misalign when they undergo changes in temperature. This in turn induces an electric current. Electric charge also collects depending on the direction of the dipoles. When the material is deformed, it also generates a current caused by specific regions repelling or attracting charges.
KBNNO’s general ferroelectric and photovoltaic properties were studied by previous researchers, but they didn’t focus on properties related to pressure or temperature. The research was also done at temperatures a few hundred degrees below freezing, making the results impractical for everyday use.
With the University of Oulu’s research, this is the first time anyone has evaluated all the properties above room temperature at the same time. The experiments conducted showed that although KBNNO is able to generate electricity from pressure and heat reasonably well, it isn’t as good as other perovskites. The researchers did however find that they are able to modify the composition of KBNNO to improve its pyroelectric and piezoelectric properties. This result is promising and it might be possible to tune all these properties to a maximum point. The team is already preparing KBNNO with sodium to explore if this would result in such an improved material.
The researchers hope to build a prototype multi-energy-harvesting device within the next year. As the manufacturing process is straightforward, commercialization could be possible in a few years from when the researchers identify the best material. When power consuming sensors and devices become energy sustainable, it will push the development of both smart cities and the Internet of Things.
It is likely that this kind of material would supplement the batteries in devices, reducing how often they need to be recharged and improving energy efficiency. Multi energy harvesting may even mean that gadgets won’t have to be plugged in anymore and that batteries for small devices may become obsolete.
The full study was published in the journal Applied Physics Letters.