Imagine the ideal world of the future. If all goes well, there will be no pollution, society will run on renewable resources, climate change will be under control, and plastics will be . . . everywhere?
Plastics get a bad rap, says Geoffrey W. Coates, Chemistry and Chemical Biology, but like it or not, we are dependent on them. It would be very hard to find replacements for all their myriad uses in modern society. Rather than doing away with them, Coates has devoted his research to finding ways to make plastics environmentally friendly at every stage of their life cycle. Along the way, he and his lab have invented an exciting lineup of plastics that may just change the way the world works.
“We make plastics that are better for the environment,” says Coates, who is a synthetic chemist. “At the beginning of their lives, our plastics are made from renewable resources and later, at the end of their lives, they degrade on a reasonable time scale into nontoxic substances.”
Polymers from Orange Peel, Pine Bark, Sugar Cane, and Soybean Oil
Coates creates plastics by synthesizing polymers, large molecules made up of smaller repeating units called "monomers." Traditionally, synthetic polymers are made from petrochemicals, but Coates has turned to renewable substances instead for his chemical building blocks. Some of the substances he has used include limonene (from orange peels), pinene (from pine bark), succinic acid (from sugar cane), and the oil from soybeans. “We can turn soybean oil into a substance indistinguishable from polyethylene,” he says with satisfaction.
To commercialize an early success, in 2004 Coates cofounded Novomer, a company based on one of his new polymers, polypropylene carbonate. Although most processes to make polymers add carbon dioxide (CO2) to the environment, Coates discovered a way to chemically build the carbon dioxide into the polymer, trapping it. “It’s basically a very rare way to capture carbon dioxide,” Coates says. “Our polymer is also biodegradable.” Novomer is now being used in adhesives, coatings, and foams.
A Polymer for a Fuel Cell
Continuing his quest to make environmentally friendly plastics, Coates and his research group have been working for eight years to create a polymer that can function as the electrolyte membrane in a fuel cell running under alkaline conditions. His involvement began when two of his department colleagues, Héctor D. Abruña and Francis J. DiSalvo, director of the Atkinson Center for Sustainability, wanted to create new materials for fuel cell electrodes to replace the platinum that is commonly used. Fuel cells are electrochemical devices that can produce energy much more efficiently than combustion engines. Traditional fuel cells made with platinum, however, are so expensive they have limited uses, even though their adoption would cut down substantially on climate-changing CO2 emissions.
“At the beginning of their lives, our plastics are made from renewable resources and later, at the end of their lives, they degrade on a reasonable time scale into nontoxic substances.”
Abruña and DiSalvo had good success with non-precious metal electrode materials, Coates explains. “The problem was that these materials dissolve in acid, and most fuel cells are run under acidic conditions.” Switching to alkaline conditions eliminated the electrode destruction but created a new problem—a lack of chemically stable electrolytes. Acidic fuel cells with platinum electrodes use a material called NafionTM for the membrane, which works extremely well under acid conditions but not under alkaline conditions. Now DiSalvo and Abruña turned to Coates and his polymer expertise to find a new membrane material that could work under alkaline conditions with the same reliability and efficiency as NafionTM.
“We knew it would be challenging,” Coates says. With funding from the Department of Energy and more recently the Ford Motor Company, he and his lab went to work. “We had some early successes, some very good conductivities, very good properties for the membranes. The problem was they would work really well in the beginning, then slowly decompose. The stability was lacking.”
Coates took that first generation of materials and studied them at the molecular level to understand how they disintegrated. “Then we went back and redesigned with the intent of getting rid of the material’s Achilles' heel,” he says. “Through a number of iterations, we came up with a really exciting class of materials that has shown absolutely no degradation when subjected to accelerated testing conditions.”
Best of all, from Coates’ perspective, this new class of polymer materials—made of phosphonium cations hooked onto a polymer backbone—can be put to a multitude of uses. “They’re not just for fuel cells,” he says. “We’re excited about their potential for use in the desalination of water, for instance. And we’re looking at applications in industrial chemical processing.”
In the summer of 2015, Coates and Abruña were invited to cofound a company called Ecolectro by two of their former graduate students, Gabriel G. Rodríguez-Calero, PhD ’14, and Kristina M. Hugar, PhD ’16, along with Robert Lewis, a graduate of the University of Pennsylvania Wharton Business School. Ecolectro aims to commercialize these new polymer materials as part of its mission to make renewable energy cost-competitive with traditional energy technologies. Cornell’s life science technology incubator, the McGovern Center, accepted Ecolectro as one of its client companies in early January 2016.
A Solid Polymer Electrolyte for Better Batteries
Looking for more ways that plastics can be used in energy storage and conversion, Coates also joined with Lynden A. Archer, Chemical Engineering, to create a better battery. Specifically, the researchers have addressed the safety problems inherent in conventional batteries that use liquid electrolytes. If the battery gets too hot, the liquid turns to gas and the battery builds up pressure and can explode or catch fire. In addition, the cycle of constant charging and discharging can cause dangerous instability issues in the battery.
While there have been batteries developed that use polymer electrolytes, they have a huge limitation when it comes to performance. To function, you have to heat them to 70 degrees Celsius. That’s a big drawback that also wastes energy. Electric cars that use these polymer electrolyte batteries, for instance, must be plugged in and drawing energy to heat the battery when they are not in use.
“We’ve developed a solid polymer electrolyte that begins to address these issues,” says Coates. “The solid polymer won’t turn into gas or ignite. It gets good performance at room temperature, and it reduces the instabilities in the charge and discharge process.”
The Coates group was able to create the new polymer because of the group’s broad skill set. “Most labs focus on one or two polymers,” Coates explains. “We make many different ones. Because of our expertise, we were able to make a new plastic from two different materials that generally don’t work well together. We took the polymers and found a way to hook them together into a new form that is more effective than the individual components."