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Fuel cells, especially those for transportation applications, must operate over a wide range of operating and cycling conditions. The desired operating range encompasses temperatures from well below freezing to well above the boiling point of water, relative humidity from ambient to saturated, and half-cell potentials from 0 to >1.5 V. Furthermore, the anode may be exposed to both hydrogen and air during different parts of the driving and start/stop cycles.Transportation fuel cell operation is greatly exacerbated by the transient and cyclic nature of the operating conditions. The cell/stack conditions cycle, sometimes quite rapidly, between high and low voltage, temperature, humidity, and gas composition. The cycling results in physical and chemical changes to components, sometimes with catastrophic results.This document describes DOE durability targets and the status of current fuel cell technology as well as accelerated stress test (AST) protocols to assess the performance and durability of PEM fuel cell components. Introduction and BackgroundCost and durability are the two most challenging barriers preventing polymer electrolyte membrane (PEM) fuel cell systems from reaching technology readiness. To reach technology readiness, automotive fuel cell power systems will be required to be as durable and reliable as today's internal combustion engines, corresponding to a 5,000 hour operating lifetime. This system target must take into account a number of factors elaborated on below. Improvements in both the mechanical integrity and tolerance to impurities of MEAs are needed.

Low cost, durable, and selective membranes with high ionic conductivity are a priority need for wide-spread adoption of polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs). Electrolyte membranes are a major cost component of PEMFC stacks at low production volumes. PEMFC membranes also impose limitations on fuel cell system operating conditions that add system complexity and cost. Reactant gas and fuel permeation through the membrane leads to decreased fuel cell performance, loss of efficiency, and reduced durability in both PEMFCs and DMFCs. To address these challenges, the U.S. Department of Energy (DOE) Fuel Cell Technologies Program, in the Office of Energy Efficiency and Renewable Energy, supports research and development aimed at improving ion exchange membranes for fuel cells. For PEMFCs, efforts are primarily focused on developing materials for higher temperature operation (up to 120 °C) in automotive applications. For DMFCs, efforts are focused on developing membranes with reduced methanol permeability. In this paper, the recently revised DOE membrane targets, strategies, and highlights of DOE-funded projects to develop new, inexpensive membranes that have good performance in hot and dry conditions (PEMFC) and that reduce methanol crossover (DMFC) will be discussed.

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