Smart supercapacitor designed to harvest, store solar energy

The push for renewable energy has spurred researchers from Clemson University and the Indian Institute of Science to design a smart supercapacitor using a novel stack of metal oxides — vanadium pentoxide and zinc oxide — that can efficiently harvest energy from sunlight and simultaneously store it.

Like batteries, supercapacitors store and release electricity. But unlike batteries, supercapacitors don’t need a chemical reaction to store electricity, as the electrical charge is stored electrostatically, which allows supercapacitors to be rapidly charged and discharged. The research could pave the way for future self-charging consumer electronics such as health monitoring devices.

Although solar energy is renewable, one challenge is that it is harvested during the day when the sun is out and must be stored for future use. That traditionally required two separate devices — one to harvest the light into electricity and another to store it. Having both can make the overall system bulky. Researchers from the lab of Indian Institute of Science Professor Abha Misa and the Clemson Nanomaterials Institute (CNI) developed a smart device that converts light to electrical energy and stores it, reducing bulkiness.

Zinc oxide has been widely used in light-dependent charge transfer applications, such as photovoltaics and photocatalysis, because of its high carrier mobility, long carrier diffusion, ease of synthesis on substrates and non-toxicity. It has electron transporting and hole-blocking characteristics and readily generates photo-excited electrons on light irradiation. However, its wide band gap restricts its utility to a narrow light spectrum, requiring a novel strategy to improve its performance.

The researchers stacked vanadium pentoxide and zinc oxide to create a unique heterostructure that improved on past materials’ ability to convert light to electrical energy. In a test to measure its ability to store harvested light, the new device reportedly bested the previous record by a factor of four.

Image caption: A supercapacitor made from vanadium pentoxide and zinc oxide can harvest and store energy from sunlight. Image credit: Clemson University

“We’ve come up with a two-in-one device that not only harvests light more efficiently but also stores it as electrical energy, unlike the other systems that exist right now. The materials we chose allowed us to engineer the band gap so that the light-to-electricity conversion was very efficient,” said Mihir Parekh, a researcher at CNI.

The device demonstrated excellent electrochemical performance and stability for over 5000 cycles.

“What we are essentially doing here is trying to harvest every ounce of energy around us in nature. We have much sunlight. The driving force behind the research is to open doors to another technology besides solar cells, which has already become a mature field, to capture the energy that is all around us,” said Apparao Rao, CNI’s founding director.

The research findings were published in the Journal of Materials Chemistry A.

Top image credit: iStock.com/Bilanol