Prototype fuel cell stack uses end plates molded from Ticona Fortron polyphenylene sulfide. The bipolar plates in the stack are made from Ticona Vectra liquid crystal polymer.

A fuel cell prototype made solely of engineering thermoplastics was recently unveiled by Ticona, Florence, Ky., the technical polymers business of the Celanese Group. The design is expected to reduce fuel cell cost at by least 50 percent versus those fabricated with other materials such as metals or thermosets.

The 17-cell unit contains injection molded bipolar plates of Ticona’s Vectra liquid crystal polymer (LCP D950 with graphite) and end plates of Ticona’s Fortron polyphenylene sulfide (PPS 1140 L0). The bipolar plates were molded by SGL Carbon, and the end plates were made by Ensinger.

The new fuel cell cuts the cost-per-kilowatt for the stack to about $1,050 (€790) from as much as the $4,000 (€3,000) needed with aluminum, gold-coated stainless steel, graphite or thermoset-graphite blends. Ticona says that the use of injection-molded thermoplastic components represents a significant step in meeting the European Union’s target cost of $665 (€500) per kilowatt by 2010 for 2 KW residential units.

The Vectra LCP bipolar plates, which contain 85 percent powdered carbon, were molded by SGL Carbon, the world’s largest producer of carbon and graphite products. With a cycle time of just 30 seconds, these plates can be produced in volume without the labor- and cost-intensive machining and other finishing steps needed to form their intricate channels when other materials are used.

"By lowering fuel cell cost to €790 per kilowatt,” says Frank Reil, manager, market development, “our prototype will help accelerate the evolution of fuel cells for autos, homes and mobile equipment. In order to meet the EU’s 2010 deadline, the industry must bring fuel cell price and weight down and extend service life.

“The use of engineering thermoplastics addresses these problems directly. Vectra LCP and Fortron PPS in bipolar and end plates reduce cost and weight compared to metal and speed production because they are injection molded. The LCP’s ability to carry a carbon loading of over 85 percent and still process well goes beyond what nearly any other plastic can do. In addition, both polymers have excellent long-term performance because they withstand the aggressive media found in fuel cells and remain dimensionally stable, even at temperatures as high as 200˚C,” Reil says.

Fuel cell, bipolar plate is made from Ticona’s Vectra liquid crystal polymer.

Fortron PPS can also be used in peripheral components to reduce costs further, as can other engineering polymers such as Celcon acetal copolymer. These resins resist aggressive substances and offer other properties needed in pumps, compressors and related components that help move fluids and gases into and away from the cells. The Ticona prototype is a proton exchange membrane (PEM) fuel cell. PEM units generate power electrochemically at high efficiency (near 40 percent) without pollution.

Each cell in a fuel cell stack has two bipolar plates and a polymer membrane. One plate acts as the anode and the other as the cathode. Surface channels in the plates distribute hydrogen and air to the membrane between them.

A thin layer of platinum catalyst on the membrane dissociates hydrogen into protons (positive hydrogen ions) and electrons. Protons pass through the membrane to the cathode. Electrons exit the stack as an electrical current before reaching the cathode, where they react with the protons and oxygen in air to form water and heat.