Researchers at the Indian Institute of Science (IISc) have developed a new type of supercapacitor that can be charged using light.
This breakthrough could be useful in a wide range of devices, including streetlights and self-powered electronics like sensors.
The study, led by Professor Abha Misra from the Department of Instrumentation and Applied Physics (IAP), was published in the Journal of Materials Chemistry A.
Supercapacitors are advanced versions of capacitors, which store energy in the form of charges on two metal plates called electrodes.
Unlike regular capacitors, supercapacitors use electrochemical processes to store much more energy. The new supercapacitor developed by Misra’s team takes things a step further by being rechargeable with light.
The researchers created the electrodes using zinc oxide (ZnO) nanorods grown on a transparent material called fluorine-doped tin oxide (FTO). These materials are semiconductors, which allow them to store energy efficiently.
The FTO lets light pass through to the ZnO nanorods, enabling the supercapacitor to be charged by light. Two different types of electrolytes—a liquid and a semi-solid gel—were used to conduct electricity between the electrodes.
One of the key properties of capacitors is their ability to store charge, which is measured as capacitance. Capacitance increases as the distance between the electrodes decreases. In traditional capacitors, keeping the electrodes very close together is difficult.
However, in supercapacitors, ions from the electrolyte gather very close to the electrodes, creating a highly efficient “electric double layer” (EDL) that boosts the capacitance.
When the researchers shone ultraviolet (UV) light on their supercapacitor, they observed a dramatic increase in capacitance—much higher than any previously reported supercapacitors. They also discovered two unusual behaviors.
Normally, capacitance decreases as voltage increases, but in this case, it actually increased, a phenomenon they call “necking behavior.” This could be due to the highly porous structure of the electrodes.
Additionally, when charged quickly under UV light, the supercapacitor stored more energy than expected, which is unusual because faster charging typically reduces energy storage.
These findings were explained using theoretical models developed by Mihir Parekh, a researcher in Professor A.M. Rao’s team at Clemson University in the U.S., who also collaborated on the study.
The team’s work opens the door to developing supercapacitors that are both fast-charging and energy-dense, making them highly efficient.
The team focused on two key strategies: increasing the surface area of the electrodes and using a liquid electrolyte to create a better electric double layer. This combination resulted in superior performance. The researchers believe that by adjusting the design, the supercapacitor could eventually be charged by visible and infrared light as well.
These new supercapacitors could have many applications, including replacing solar cells in streetlights or powering microchips in electronic devices.
The IISc team is continuing to refine the design, hoping to make even more powerful versions in the future.
