Research published in the journal Energy Storage reports on the development of a supercapacitor that is literally plant-based. Made from lignin, which enhances the electrochemical properties of electrodes, the supercapacitor designed by scientists at Texas A&M University is flexible, lightweight, cost-effective – and most importantly, fast. According to the researchers, the supercapacitor has enough energy storage that could even charge electric cars within a few minutes in the near future.
"Integrating biomaterials into energy storage devices has been tricky because it is difficult to control their resulting electrical properties, which then gravely affects the devices' life cycle and performance. Also, the process of making biomaterials generally includes chemical treatments that are hazardous," said Dr. Hong Liang, a professor in the Department of Mechanical Engineering. "We have designed an environmentally friendly energy storage device that has superior electrical performance and can be manufactured easily, safely, and at a much lower cost."
Supercapacitors are unique from batteries in their ability to generate a large quantity of electric current within a short duration. This means that supercapacitors can charge devices much faster than batteries.
Dr. Liang and her team used manganese dioxide nanoparticles to design one of the two supercapacitor electrodes. Supercapacitor electrodes, unlike basic capacitors, can be constructed with a variety of materials.
"Manganese dioxide is cheaper, available in abundance and is safer compared to other transition metal oxides, like ruthenium or zinc oxide, that are popularly used for making electrodes," said Dr. Liang. "But a major drawback of manganese dioxide is that it suffers from lower electrical conductivity."
That’s why Liang’s team brought in lignin polymers. Using a purified lignin with a commonly available disinfectant known as potassium permanganate, the team was able to construct an electrode for their capacitor. As explained by Eureka Alert, the researchers “…applied high heat and pressure to initiate an oxidation reaction that results in the breaking down of potassium permanganate and the deposition of manganese dioxide on lignin. Next, they coated the lignin and manganese dioxide mixture on an aluminum plate to form the green electrode. Finally, the researchers assembled the supercapacitor by sandwiching a gel electrolyte between the lignin-manganese dioxide-aluminum electrode and another electrode made of aluminum and activated charcoal.”
This process resulted in a supercapacitor with superior electrochemical performance, with a specific capacitance up to 900 times greater than that of supercapacitors. Additionally, the supercapacitor’s ability to store an electrical charge did not suffer even after thousands of cycles of charging and discharging.
"In this study, we have been able to make a plant-based supercapacitor with excellent electrochemical performance using a low-cost, sustainable method," concluded Liang. "In the near future, we'd like to make our supercapacitors 100% environmentally friendly by incorporating only green, sustainable ingredients."