Science Alliance Annual Report
2008–2009
UT-ORNL Distinguished Scientists
UTK chemistry; ORNL chemical sciences
Jimmy Mays
Polymer fuel cell membranes
The hydrogen fuel cell has potential as a lightweight, green energy resource for automobiles and other applications. Simple in concept, the cell strips positively charged protons from pure hydrogen entering the cell on the anode side. These are drawn through a semipermeable membrane by an oxygen-rich cathode on the other side of the cell. Meanwhile, the electrons enter an external circuit, supply electrical power for motors and other equipment, and reenter the cell on the cathode side, where it and hydrogen protons unite with oxygen and become water.
The polyelectrolyte or proton exchange membrane separating the anode and cathode is key to a fuel cell’s operation. Developing inexpensive, robust, highly conductive membranes that will stand up to the elevated temperatures and low relative humidity inside fuel cells is one of the details standing in the way of success.
Under Department of Energy sponsorship, Jimmy Mays’s team, (notably Suxiang Deng, UTK postdoctoral fellow in chemistry), synthesized and patented membranes based on an inexpensive hydrocarbon polymer base. Tests show the membranes are thermally and chemically stable and conduct protons better than Nafion at a fraction of the cost. Nafion, an expensive DuPont product, is the membrane-of-choice used in most fuel cells today.
Mays’s group is exploring other potential uses for their membrane, including for water desalination and inside batteries.
Improving polymer synthesis
In work for the National Science Foundation, Mays’s group is working with a team of rheologists and theorists to improve synthesis methods for specific well-defined branched polymers. Branched polymers are macromolecules with side chains dangling from a backbone.
Long branches dramatically affect how a polymer flows, a critical point because many products are manufactured from melted material under high shear conditions—for example the polymer films that become kitchen wrap or polymer fibers used in disposable diapers.
Polymer chemists learned long ago that branched polymers can be processed more easily and at higher rates than linear polymers (those with chains that go on and on) Mays says. But, too much branching, and you compromise polymer strength and solvent resistance.
The discovery, some ten years ago, of metallocene catalysts for making polyolefins, such as polyethylene and polypropylene, made it possible for scientists to synthesize polymers with a small number of exceptionally long branches. This process takes advantage of the benefits of branching without compromising strength; but the exact nature of the branching remains unknown.
Mays and his team will study these molecular structures to discover how particular branched architectures affect the flow of the material. Their results will help to develop less expensive plastics with better performance.
Mays received the 2008 Distinguished Service Award from the American Chemical Society Division of Polymer Chemistry and was the 2009 Bayer Lecturer at Cornell University. This lecture series focusing on polymer chemistry began in 1987.