Some of the 300 million tires discarded each year in the US could be recycled and used in electrodes for supercapacitors, using a new technology developed at Oak Ridge National Laboratory and Drexel University.
The process is described in a paper published in ChemSusChem, titled â€œWaste Tire Derived Carbon-Polymer Composite Paper as Pseudocapacitive Electrode with Long Cycle Life.â€
The ORNL and Drexel researchers produced flexible polymer carbon composite films, using waste tires as a precursor. The narrow pore-size distribution and high surface area led to good charge storage capacity, especially when used as a 3D nanoscaffold to polymerize polyaniline (PANI). The resulting composite paper was highly flexible and conductive, and exhibited a capacitance of 480â€…Fâ€‰gâˆ’1 at 1â€…mVâ€‰sâˆ’1 with capacitance retention of up to 98% after 10,000 charge/discharge cycles.
To produce the carbon composite paper, the researchers soaked crumbs of tire rubber in sulfuric acid, then washed the rubber and baked it at 1,100 degrees Celsius under a flowing nitrogen gas atmosphere (what fun!). After several additional steps, they had a material they could mix with polyaniline, an electrically conductive polymer.
Manufacturers expect to produce some 1.5 billion tires per year by 2035.
â€œThose tires will eventually need to be discarded, and our supercapacitor applications can consume several tons of this waste,â€ said team leader Parans Paranthaman. â€œCombined with the technology weâ€™ve licensed to two companies to convert scrap tires into carbon powders for batteries, we estimate consuming about 50 tons per day.â€
Thatâ€™s a fraction of the 8,000 tons that need to be recycled every day, but co-author Yury Gogotsi of Drexel noted that other recycling companies could contribute to that goal.
â€œEach tire can produce carbon with a yield of about 50 percent with the ORNL process,â€ Gogotsi said. â€œIf we were to recycle all of the scrap tires, that would translate into 1.5 million tons of carbon, which is half of the annual global production of graphite.â€
â€œWe anticipate that the same strategy can be applied to deposit other pseudocapacitive materials with low-cost tire-derived activated carbon to achieve even higher electrochemical performance and longer cycle life, a key challenge for electrochemically active polymers,â€ Gogotsi said.