PEDOT, short for poly(3,4-ethylenedioxythiophene), is a flexible, transparent film often applied to the surfaces of photographic films and electronic components to protect them from static electricity. It is also found in touch screens, organic solar cells and electrochromic devices, such as smart windows. However, PEDOT’s potential for energy storage has been limited because commercially available PEDOT materials lack the electrical conductivity and surface area needed to hold large amounts of energy.
An example of how EDOT monomer vapors react with a droplet of graphene oxide and ferric chloride to form PEDOT nanofibers. Image credit: UCLA
UCLA chemists have addressed these challenges with an innovative method that makes use of graphene oxide to control the morphology of PEDOT to grow nanofibers precisely. These nanofibers exhibit exceptional conductivity and expanded surface area, both of which are crucial for enhancing the energy storage capabilities of PEDOT. This approach demonstrates the potential of PEDOT nanofibers for supercapacitor applications.
Supercapacitors require materials with enough surface area to hold large amounts of energy. Traditional PEDOT materials fall short in this regard, which limits their performance.
The UCLA chemists produced the new material through a unique vapor-phase growth process to create vertical PEDOT nanofibers. These nanofibers, resembling dense grass growing upward, dramatically increase the material’s surface area, allowing it to store more energy. By adding a drop of liquid containing graphene oxide nanoflakes and ferric chloride on a graphite sheet, the researchers exposed this sample to a vapor of the precursor molecules that eventually formed the PEDOT polymer. Instead of developing into a very thin, flat film, the polymer grew into a thick, fur-like structure, significantly increasing the surface area compared to conventional PEDOT materials.
“The material’s unique vertical growth allows us to create PEDOT electrodes that store far more energy than traditional PEDOT,” said corresponding author and UCLA materials scientist Maher El-Kady. “Electric charge is stored on the surface of the material, and traditional PEDOT films don’t have enough surface area to hold very much charge. We increased the surface area of PEDOT and thereby increased its capacity enough to build a supercapacitor.”
The authors used these PEDOT structures to fabricate supercapacitors with excellent charge storage capacity and extraordinary cycling stability, reaching nearly 100,000 cycles. The advance could pave the way for more efficient energy storage systems, directly addressing global challenges in renewable energy and sustainability.
“A polymer is essentially a long chain of molecules built out of shorter blocks called monomers,” said El-Kady. “Think of it like a necklace made from individual beads strung together. We heat the liquid form of the monomers inside a chamber. As the vapors rise, they react chemically when they come in contact with the surface of the graphene nanoflakes. This reaction causes the monomers to bond and form vertical nanofibers. These nanofibers have (a) much higher surface area, which means they can store much more energy.”
The new PEDOT material has shown impressive results, exceeding expectations in several critical areas. Its conductivity is 100 times higher than that of commercial PEDOT products, making it far more efficient for charge storage. What's even more remarkable is that the electrochemically active surface area of these PEDOT nanofibers is four times greater than that of traditional PEDOT. This increased surface area is crucial because it allows for much more energy to be stored in the same volume of material, significantly boosting the performance of supercapacitors.
Thanks to the new process, which grows a thick layer of nanofibers on the graphene sheet, this material now has one of the highest charge storage capacities for PEDOT reported to date — more than 4600 milliFarads per square centimeter, which is nearly one order of magnitude higher than conventional PEDOT. On top of that, the material is incredibly durable, lasting through more than 70,000 charging cycles, far outlasting traditional materials. These advances open the door for supercapacitors that are not only faster and more efficient but also longer-lasting, which are essential qualities for the renewable energy industry.
“The exceptional performance and durability of our electrodes shows great potential for graphene PEDOT’s use in supercapacitors that can help our society meet our energy needs,” said corresponding author Richard Kaner, a UCLA distinguished professor of chemistry and of materials science and engineering.
