Life cycle assessment of PEM FC applications: electric mobility and μ-CHP
Polymer electrolyte membrane fuel cells (PEM FCs) are seen as a suitable technology supporting the transformation towards decarbonised societies. Decision makers face the problem that there is no sound basis of the environmental performance of cutting edge technology available. We developed a comprehensive product system for two types of high temperature (HT) PEM FCs and conducted a life cycle assessment. One system utilizes functionalized multiwalled carbon nanotubes (MWCNTs) as carbon support materials for platinum. The reference product applies carbon black. MWCNTs render possible platinum savings of 27% simultaneously retaining equal performance parameters as for the reference FC. The inventories include all components of a FC starting with the production of the carbon support material, the catalyst powder with platinum nanoparticles, a membrane, a gas diffusion layer, bipolar flow plates up to the FC stack and the FC unit including end of life treatment. Our analysis shows that platinum is the key material in HT PEM FCs and the benefits from platinum savings outweigh by far the impacts on the MWCNT production. The HT PEM FC was adjusted such that it typifies (1) a PEM FC for an electric vehicle (FCEV) allowing comparison with internal combustion engine vehicles (ICVs) and battery electric vehicles (BEVs) or (2) a PEM FC suitable for micro-combined heat and power (μ-CHP) to be compared with a Stirling engine. We found an environmental advantage of a FCEV vis-à-vis the ICV, but only if hydrogen is produced with renewable electricity. We found similar environmental impacts for the FCEV and the BEV when both vehicles are propelled with renewable energy. Both μ-CHP plants produce similar amounts of useful energy and have comparable environmental performance. Nonetheless, the PEM FC produces more electricity (less heat) than the Stirling engine. System expansion such that both systems deliver equal amounts of electricity and heat resulting in an advantage of nearly 20% for the PEM FC powered system. Thus, the PEM FC technology offers great potential to reduce a personal environmental (and carbon) footprint – a prerequisite on the way of a transformation to more sustainable societies.