Polymer electrolyte fuel cell (PEFCs) technology has advanced to reach the commercialization stage with more automotive manufacturers announcing new PEFC-based light and heavy-duty vehicles. However, the life span and cost of such systems still remain challenges. Using the Department of Energy (DOE) cost-breakdown for the 80-kWnet stack for light-duty vehicles, the cost of precious metal electrocatalysts remains almost unchanged as production rate increases to 0.5 M PEFC stacks per year. The cost of the electrocatalysts amounts to 31% of stack cost, for 0.5 M systems per year production rate. Platinum (Pt) or Pt-alloys are used as electrocatalysts for the oxygen reduction reaction (ORR) on the cathode side and the hydrogen oxidation reaction (HOR) on the anode side of PEFCs. Pt or Pt-alloy electrocatalysts are dispersed as nanoparticles onto a carbon-black support. DOE set a target of reducing Pt loading to 0.125 mg cm-2 to achieve the goal of $12.6 kWnet -1 for a stack with power density target of 1.8 W cm-2. MEAs with lower catalyst loading are less durable [1], thus, the cost issue cannot be resolved without focusing on the catalyst durability issue of the PEFC stack. To reach the activity and durability targets, overall understanding of the interfaces within the MEAs are needed and their evolution during ageing.This presentation will summarize my group’s recent efforts within the three main directions for the MEA design: 1) catalyst layer durability studies, via advanced characterization [2], 2) Pt-ionomer interface understanding during the PEFC lifetime and its impact on activity and durability and, 3) ionic liquids and small molecule additives to tailor Pt-ionomer interface for activity. Using methodology of electrochemical characterization, including CO-displacement/stripping, double layer capacity studies, oxygen transport resistance measurements, and others, along with the computational modeling and advanced material characterization (synchrotron and lab-scale), we aim to build comprehensive understanding of transport properties, water management and interfacial properties during the PEFCs’ lifetime.