Minimizing mass-transport loss in proton exchange membrane fuel cell by freeze-drying of cathode catalyst layers

Abstract

The widespread commercialisation of proton exchange membrane fuel cell (PEMFC) for either transportation or stationary application is still hindered by cost barriers owing to the use of precious metal catalysts, as well as performance and material related insufficient durability. Therefore, it is important to enhance the platinum utilization as well as optimize the fabrication method for the production of membrane electrode assemblies (MEAs). This study demonstrates that the drying step during the electrode manufacturing directly affects the microstructure of the catalyst layer, having inherent influence on the porosity and the platinum utilization during PEMFC operation that greatly affects the performance. Freeze-drying as a novel drying technique for PEMFC electrodes is proposed for preparation of low Pt-loaded cathodes (0.160 mgPt·cm−2). This technique possesses the unique feature of solvent removal via sublimation and not only generates 3.5-fold higher effective porosities but also increases the electrochemical surface area by 1.5 times when comparing to electrode dried by regular oven drying technique. Additionally, freeze-drying of electrode also improved ionomer distribution, as evident from a reduced resistance between the pores and a reduced electrolyte resistance of the catalyst layer. Consequently, we consider freeze-drying to be a highly promising technique for future production of MEAs.