The biggest issues to popularize fuel cell electric vehicles (FCEVs) in the market are cost reduction of polymer electrolyte fuel cell (PEFC) power system, and development of hydrogen infrastructure. Related to the former issue, one of the most significant challenges is to reduce platinum group metals (PGM) in fuel cell stacks. PGM are used as electrocatalyst and contained in catalyst layers (CLs) of membrane electrode assemblies (MEAs) in the stack.
A lot of research activities on PEFC electrocatalyst have been reported so far, indicating high oxygen reduction reaction (ORR) activity and durability mainly measured in aqueous electrolyte systems such as a rotating disk electrode method.2-8 On the other hand, electrocatalyst is mixed with electrolyte to form CLs through deposition and solidification process. From industrial point of view, it is needed that performance of the electrocatalyst should be guaranteed as CL in MEA. CL is a multi-scale component, i.e. micro-scale porous electrode consisting of nano-scale materials, where electrochemical reaction and mass transport occur simultaneously. Micro and nano structure of CL has been revealed gradually by means of characterization techniques remarkably progressed recently, such as electron microscope.9,10 However, it is still under development to characterize and diagnose structure and properties of CLs as overall and average value.
To design low-PGM loaded CLs without scarifying performance, Nissan has been trying to understand the correlation between materials and CL/MEAs through properties and structure via key mechanism.11-15 Recently, process analysis such as catalyst ink microstructure has been more focused.16-18 In this presentation, current status and challenges of CL/electrocatalyst design and development at Nissan will be introduced.
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