Are we chasing the right horse?
Following the presentation of Thomas Wannemacher (Proton Motor) during the Manufacturing workshop organised by the INSPIRE team in Marseille, a debate started on the topic of the usefulness of graphite-polymer bipolar plates. According to some, metallic bipolar plates are a clear winner due to their superior electric conductivity, mechanical properties, ease of mass manufacture and the smaller cell pitch. Furthermore, due to the fast processes the capability of producing very high volumes in appropriate short time is given, combined with a potential of moderate production costs. Others refer to the still developing coating systems needed to keep the corrosion processes under wraps. Certainly, Proton Motor has to have a good reason to stay with the graphite-polymer alternative.
To provide some perspective, there are two obvious routes in the exploitation of fuel cells: low current density operation leveraging the high efficiency and ensuring endurance when compared to conventional power sources and high current and power density capability requested by the automotive industry to sever the umbilical cord to oil and meet the stringent yet sorely needed targets imposed on CO2 emissions. While the entire fuel cell industry will surely benefit from the pursuit of ever higher power densities at lower catalyst loading, there are many areas with more conservative needs.
In the Fit-4-AMandA project, UPS expect that the delivery vans will last considerably longer that the 6000-hour mark requested in the recent Horizon 2020 calls. Given the nature of operation, light-commercial vehicles post a much higher mileage than their passenger counterpart. A UPS package logistics van can reach up to 50.000km per year and remains much longer in service. Operating as a range extender, the dynamic load shifts and start-stop cycles are covered by the battery packs, which are kept at the optimum state of charge by the fuel cell, while the fuel cell can operate optimally and almost in a stationary state. The joined forces of batteries and fuel cell allow the LCVs to enter highways without sacrificing range, travel farther, and the combination is also lighter, allowing for a heavier payload.
In terms of weight metallic and graphitic based bipolar plates are rather comparable and in most of the “long life applications” the disadvantage of the higher volume (lower power density) is still not so dramatic since space requirements are not limited as in a passenger car.
And for commercial duty vehicles the required numbers of systems are far away from automotive passenger cars. Hence the capacity of producing graphitic based bipolar plates will last for the next couple of years. Even more if the plates are considered to have a “second life” after the electrochemical parts (MEA) reached end of life in operation in a high duty application. This can be possible because the graphitic polymer plates are chemically rather inert and not undergoing major ageing processes.
Meanwhile, the lifetime expectations of the metallic plates accompanied with improved coating technology may enhance dramatically. But, according to our consortium, within this time slot the graphite polymer plates are preferred for long life application in mobile, maritime and of course stationary applications.