Introduction of proton‐exchange membranes as solid electrolytes has permitted the development of fuel cells that utilize hydrogen, reformate gas and methanol as reactants. Modern fuel cells have extended service life and reliability and increased power and energy density. The need for fuel cell operating in excess of 5000 h for transportation and 30 000 h for stationary applications has led to extensive investigations of the failure modes in an effort to understand the primary mechanical, chemical and electrochemical mechanisms. This chapter reviews the progress in understanding the limitations of fuel cell operation with historical and current state‐of‐the‐art membranes and suggests directions for achieving further improvement.

Fuel cells that can operate directly on fuels such as methanol are attractive for low to medium power applications in view of their low weight and volume relative to other power sources.A liquid feed direct methanol fuel cell has been developed based on a proton exchange membrane electrolyte and Pt/Ru and Pt catalyzed fuel and air/O2 electrodes respectively.The cell has been shown to deliver significant power outputs at temperatures of 60 to 90* C. The cell voltage is near 0.5 V at 300 mA/cm 2 current density and an operating temperature of 90* C. A deterrent to performance appears to be methanol crossover through the membrane to the oxygen electrode.Further improvemerits in performance appear possible by minimizing the methanol crossover rate.

The measurement of alcohol consumption over long time periods is important for monitoring treatment outcome and for research applications. Giner, Inc. has developed a wearable device that senses ethanol vapor at the surface of the skin, using an electrochemical cell that produces a continuous current signal proportional to ethanol concentration. A thermistor monitors continuous contact of the sensor with the skin, and a data-acquisition/logic circuit stores days of data recorded at 2- to 5-min intervals. Testing of this novel ethanol sensor/recorder was conducted on nonalcoholic human subjects consuming known quantities of ethanol and on intoxicated alcoholic subjects. The transdermal sensor signal closely follows the pattern of the blood alcohol concentration curve, although with a delay. This paper describes the concept of electrochemical ethanol measurement and presents some of the clinical data collected in support of the sensor/recorder development.

This paper summarizes some of the progress that has been made over the past 30 years in identifying chemical and mechanical degradation mechanisms in proton-exchange membrane fuel cells (PEMFCs), as well as approaches in refining stack operating conditions, cell hardware configurations and membrane-electrode assembly (MEA) stabilization to mitigate degradation and extend life. New analytical methods have been brought to bear to understand the relationships between PEM degradation and fuel cell operating conditions, especially low relative humidity, elevated temperatures, and frequent open-circuit periods. PEM/MEA degradation similar to that observed in PEMFC may also occur under certain accelerating conditions for protonexchange membrane water electrolyzers (PEMELCs) that typically operate for 30 to 100 thousand hours without incident when properly hydrated, thermally managed and mechanically supported. A comparison is made of common hardware and operational factors for PEMELCs and PEMFCs that can lead to PEM/MEA degradation.

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Several factors impacting chemical degradation of perfluorinated sulfonic acid ionomers are identified in this paper. Based on the results from this study, gas crossover is the fundamental mechanism that leads to PFSA membrane chemical degradation. H2, O2 and a catalytic surface are required to generate H2O2/radicals. The effect of electrochemically generated Pt oxide/hydroxide, Vulcan® XC-72R, Pt/C is clarified. Two major degradation pathways, H2O2 Pathway and Direct Radical Generation Pathway, are proposed. The impact of iron contamination and H2O2 concentration is also discussed. It was shown that a H2O2 flow cell is a better approach for membrane/MEA evaluation than conventional beaker based Fenton's tests (i.e., batch-like tests).

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