Researchers at the Department of Instrumentation and Applied Physics (IAP), Indian Institute of Science (IISc), have designed a novel ultramicro supercapacitor, a tiny device capable of storing an enormous amount of electric charge, the institute said in late March.
The device is much smaller and more compact than existing supercapacitors and can potentially be used in streetlights, consumer electronics, electric cars, and medical devices.
Most devices currently in use are powered by batteries. However, over time, these batteries lose their ability to store charge, which limits their shelf life. Capacitors, on the other hand, can store electric charge for much longer. But unlike batteries, they cannot discharge energy constantly to power devices.
Supercapacitors, on the other hand, can store as well as release large amounts of energy, and are therefore highly sought after for next-generation electronic devices.
In a study published in ACS Energy Letters, the researchers said they fabricated their supercapacitor using Field Effect Transistors (FETs) as the charge collectors, instead of metallic electrodes used in existing capacitors. “Using FET as an electrode for supercapacitors is something new for tuning charge in a capacitor,” said Abha Misra, corresponding author of the study.
Current capacitors typically use metal oxide-based electrodes, but they are limited by poor electron mobility. Therefore, Misra and associates decided to build hybrid FETs consisting of alternating few-atoms-thick layers of molybdenum disulphide and graphene, to increase electron mobility, that were then connected to gold contacts. A solid gel electrolyte was used between the two FET electrodes to build a solid-state supercapacitor. The entire structure was built on a silicon dioxide/silicon base.
According to lead author Vinod Panwar, fabricating the device was challenging. Since these supercapacitors are very small, they cannot be seen without a microscope, and the fabrication process requires high precision and hand-eye coordination.
Once the supercapacitor was fabricated, the researchers measured the electrochemical capacitance or charge-holding capacity of the device by applying various voltages. They found that under certain conditions, the capacitance increased by 3,000 per cent. In contrast, a capacitor containing just molybdenum disulphide without graphene showed only an 18 per cent enhancement in capacitance under the same conditions.
The researchers now plan to explore other materials to further increase the capacitance.