Automotive supplier Schaeffler has developed a new generation of bipolar plates for fuel cells. The plates have a new design developed for large-scale production. A new coating process also ensures a longer service life. According to Schaeffler, stacks equipped with these achieve a power density that is about 20% higher than stacks with the plates of the previous generation.
The bipolar plates are about the size of an A4 envelope and weigh around 60 g. In the fuel cell, they separate and distribute the process gases as well as the coolant and discharge the water produced by the chemical reaction.
"Schaeffler has developed an innovative design that makes optimum use of the available surface area of the plates. This is because the finer and more precise the structures on the bipolar plates are, the more efficiently they work," says Dr. Jochen Schröder, head of the E-Mobility division at Schaeffler.
In this way, the supplier realizes a power density of the fuel cell stack of 4.6 KW per l, based on the stack volume including the end plates and bracing.
Longer service life thanks to new coating
The new bipolar plates also feature a special coating system. The task of the coating is to maintain high electrical conductivity over the entire service life of the fuel cell. With the so-called "Enertect" family, Schaeffler has developed several high-performance coating systems specifically for bipolar plates, which - depending on customer requirements - are aimed at particularly high service life requirements, the lowest possible CO₂ footprint, or an optimized price/performance ratio.
"Our expertise in surface technology enables us to offer each customer an application-specific coating development, balancing costs, performance and CO₂ emissions during production as required," says Jochen Schröder.
The coating systems are applied using the physical vapor deposition (PVD) process. This process was adopted from the production of highly stressed valve train components and further refined. Finally, leak tightness is another key quality and safety criterion for a fuel cell. For this purpose, Schaeffler uses both a laser welding process developed in-house to make the cells gas- and water-tight, as well as either injection-molded or screen-print seals.
Automated production
In Herzogenaurach, the company manufactures the new panels for numerous prototypes and small series of up to several tens of thousands of units for international vehicle manufacturers. The pilot production line set up at the site is part of a hydrogen competence center that also includes test rigs and testing facilities. The automated manufacturing plant is also designed to produce larger plates for electrolysers.
"Schaeffler is also relying on hydrogen to power commercial vehicles, especially for long-distance travel. We are developing both individual components and subsystems for fuel cells and preparing their industrialization," says Matthias Zink, Member of the Executive Board of Schaeffler AG responsible for Automotive Technologies.
