H. R. Kunz

Membrane Degradation Mechanisms and Accelerated Durability Testing of Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) have increasingly received worldwide attention as the technology that can lead to substantial energy savings and reductions in imported petroleum and carbon emissions. Cost, durability, performance, reliability, efficiency, and size, are some of the requirements that must be met before PEMFCs can be used commercially. The lifetime requirement for stationary applications is about 40,000 hours and for transportation applications 5,000 (cars) and 20,000 hours (buses) (1). Today, the typical operating temperature for both applications is between 60 – 80°C, but to meet the 2010 and 2015 Department of Energy targets, PEMFCs must operate at temperatures from below the freezing point to higher than 100°C (~120 °C maximum), humidity from ambient to saturated, and half-cell potentials from 0 to >1.5 V. Durability studies of proton exchange membrane fuel cells (PEMFC) show that, along with cost, the long-term stability of PEMFCs is a limiting factor in their commercialization (2-6). Degradation of PEM fuel cells is generally observed as slow, unrecoverable performance decay, followed by sudden failure. The gradual performance loss is typically associated with changes in the electrodes and the membrane. The degradation of electrodes is usually caused by catalyst degradation and carbon corrosion. Membrane chemical and mechanical degradation are related to reactant gas crossover, Pt dissolution and migration, transition metal ion contaminants, and hydroxyl radical formation, and cycling of relative humidity. The chemical decomposition of the side

Effect of Water Management Schemes on the Membrane Durability in PEMFCs

The authors report the degradation behavior of polymer-electrolyte membrane fuel cells tested under two types of water-management schemes: the solid plate (SP) cells that mange water via flow and dew point control of the reactant gases, and water transport plate (WTP) cells that actively remove liquid through micro-porous bipolar plates. Comparative experiments were conducted. Cell performance degradation was tracked by periodic diagnostic testing. After cell testing, the residual mechanical strength of the membrane electrode assemblies was characterized. It was found that both water management schemes led to cell performance reduction via the loss of the electrochemical active area. However, the SP cell led to rapid reduction of membrane toughness. The WTP cell tended to preserve the membrane mechanical toughness better. Post-analysis found localized membrane failure in SP cell test during which a step change in performance occurred. Abrupt performance degradation was not observed for either of the WTP cell tests.

Accelerated Durability Testing of Perfluorosulfonic Acid MEAs for PEMFCs Using Different Relative Humidities

Polymer electrolyte membrane fuel cells (PEMFCs) receive worldwide attention as the electricity-generating engine for the hydrogen economy. Cost, durability, performance, reliability, efficiency, and size, are some of the requirements that must be met before PEMFCs can be expanded commercially. The lifetime requirement for onsite, combined heat and power applications is about 40,000 hours and for transportation applications 5,000 (cars) and 20,000 hours (buses). Membrane durability is one of the most important factors limiting the lifetime of PEMFCs.

Accelerated Durability Testing of Perfluorosulfonic Acid MEAs for PEMFCs

There is a strong interest in durability studies of proton exchange membrane fuel cells (PEMFC) because, along with cost, the long-term stability of PEMFC is a limiting factor in their commercialization. Examining the characteristics of a membrane electrode assembly (MEA) over a prescribed amount of time under accelerated degradation conditions can give an indication of the degradation behavior of each MEA. Testing under low humidities and/or high temperatures or by humidity or temperature cycling are techniques that accelerate degradation.

Effect of Equivalent Weight of Phosphotungstic Acid-Incorporated Composite Membranes on the High Temperature Operation of PEM Fuel Cells

Fuel cells have shown great promise for future power sources and there has been substantial advancement in the technology of fuel cells over the past decades. For automobile application, however, there are still challenging issues related to its performance and durability. It is highly desirable to operate fuel cells at high temperature because of a number of benefits, e.g., improved reaction kinetics and carbon monoxide tolerance. Since the conventional polymer electrolytes such as Nafion are not stable at high temperatures, the development of novel membranes that are mechanically, thermally, and electrochemically stable at high temperatures while providing good conductivity under low relative humidity condition is one of the most challenging areas of research for automobile applications of fuel cells. In fact, extensive research efforts have been made to design new proton exchange materials that can overcome the limitations of conventional polymer electrolytes.