Researchers Introduce a Supercapacitor that Use Light Energy for Self-Sustaining Operation
Overview
Researchers from IISc's Department of Instrumentation and Applied Physics have developed a supercapacitor that charges with light, suitable for streetlights and self-powered sensors.
Advancements in Supercapacitor Technology
Enhanced Electrochemical Storage
According to Abha Mishra, Professor at IAP, supercapacitors are an advanced form of capacitors that use electrochemical reactions to store greater amounts of energy, as discussed in her study published in the Journal of Materials Chemistry A.
Breakthrough in Electrode Design
In a breakthrough by Pankaj Singh Chauhan from Mishra's IISc group, the new supercapacitor incorporates zinc oxide (ZnO) nanorod electrodes directly on transparent fluorine-doped tin oxide (FTO).
The photo-rechargeable supercapacitor benefits from the complementary semiconductor properties of ZnO and FTO's transparency allowing light to energize ZnO nanorods, enhancing performance. Chauhan details that a liquid and a semi-solid gel electrolyte were employed to conduct between the electrodes.
Capacitance and Performance Observations
Impact of Electrode Distance
The ability of a system to store electrical charges (capacitance) decreases as the separation between its electrodes increases.
Mishra explains that as electrode distance decreases significantly, capacitance increases dramatically. In electrostatic capacitors, keeping electrodes close is challenging, but supercapacitors achieve high capacitance by forming an electric double layer (EDL) where the charges attract oppositely charged ions in the electrolyte, effectively creating a charge layer just atoms apart.
Unusual Behaviors Under UV Light
The researchers observed a dramatic rise in capacitance, several times greater than previous supercapacitors, when ultraviolet (UV) light was applied to their device. Additionally, they noted two atypical behaviors: normally, capacitance drops with rising voltage, but in their supercapacitor, capacitance increased under light exposure with increasing voltage.
Explanation of Observations
A.M. Rao, Professor at Clemson University and co-author, refers to this phenomenon as "necking behavior," attributing it to the high porosity of the electrodes. Her further notes that typically, energy storage in supercapacitors diminishes with faster charging rates due to slower ion movement. However, with their liquid electrolyte, the team observed an unexpected increase in energy storage during rapid charging under UV light.
Theoretical Models and Future Directions
Insights from Theoretical Models
Mihir Parekh, a postdoctoral researcher in Rao's team, has developed theoretical models to account for these innovative observations. He indicates that these discoveries could enable the advancement of supercapacitors that are both capable of rapid charging and high in energy density.
Design Innovations
The development of their new supercapacitor involved two key approaches. The team increased the electrode surface area by combining two optically active semiconductor interfaces, enhancing light interaction and charge generation. They also utilized a liquid electrolyte to ensure an efficient electric double layer (EDL), leading to improved performance.
Future Prospects and Applications
Potential Enhancements
According to Mishra, the ideas were simple in themselves, but their combination yielded excellent results. She suggests that modifying the supercapacitor design could allow it to be charged with both visible and infrared light. The IISc-Clemson team intends to delve deeper into these novel phenomena to enhance supercapacitor design.
Practical Applications
Mishra points out that supercapacitors offer numerous applications, including the potential replacement of solar cells in streetlights. Their ability to release charge quickly due to high power density makes them ideal for powering chips in electronics like cell phones.
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