Timothy W. Patterson

Damage to the Cathode Catalyst of a PEM Fuel Cell Caused by Localized Fuel Starvation

This paper examines damage to the cathode catalyst layer of a polymer electrolyte membrane (PEM) fuel cell caused by restriction of hydrogen access to a portion of the anode catalyst layer. The results show severe damage to the majority of the cathode catalyst behind the obstruction after 100 h of operation. A portion of the cathode catalyst layer near the outside edge of the obstruction remains undamaged.

Systems Strategies to Mitigate Carbon Corrosion in Fuel Cells

The oxidation of carbon used as catalyst support in state-of- the art fuel cells is a serious decay mechanism that must be mitigated in order to achieve acceptable performance stability. Although the corrosion of carbon is certainly not a new concern for fuel-cell developers, a number of fairly recent developments have brought this issue to the forefront. These concerns include the unique operating conditions of transportation applications, the discovery of a mechanism that results in higher-than-expected potentials (i.e., the reverse- current mechanism), and the use of certain materials (e.g., high surface area carbon supported catalysts with high Pt mass fractions). Since improvements in catalyst-support stability typically comes at the expense of performance (and/or cost), and these improvements alone will be insufficient for many applications, system-mitigation strategies are required. A number of system strategies that have been developed and demonstrated at UTC Power will be described.

Capillary Pressure Saturation Relations for PEM Fuel Cell Gas Diffusion Layers

Capillary pressure saturation relations (CPSRs) are presented for Toray TGP-H-060 and Mitsubishi rayon carbon fiber paper which can both be used as gas diffusion layers (GDLs) in proton-exchange membrane fuel cells (PEMFCs). The saturation is measured using water over a range of capillary pressures. Boundary and scanning curves for imbibition and drainage are measured to further understand the hysteresis observed during PEMFC operation. The primary source of hysteresis in CPSRs is attributed to the difference in advancing and receding contact angles. The measured hysteresis is predicted to have a significant effect on mass transport in the GDL and thus performance in PEMFCs.

Operating Requirements for Durable Polymer-Electrolyte Fuel Cell Stacks

Successful developers of fuel cells have learned that the keys to achieving excellent durability are controlling potential and temperature, as well as proper management of the electrolyte. While a polymer-electrolyte fuel cell (PEFC) has inherent advantages relative to other types of fuel cells, including low operating temperatures and an immobilized electrolyte, PEFC stacks also have unique durability challenges owing to the intended applications. These challenges include cyclic operation that can degrade materials owing to significant changes in potential, temperature, and relative humidity. The need for hydration of the membrane as well as the presence of water as both liquid and vapor within the cells also present complications. Therefore, the development of durable PEFC stacks requires careful attention to the operating conditions and effective water management.

PEM Fuel Cell Freeze Durability and Cold Start Project

UTC has taken advantage of the unique water management opportunities inherent in micro-porous bipolar-plates to improve the cold-start performance of its polymer electrolyte fuel cells (PEFC). Diagnostic experiments were used to determine the limiting factors in micro-porous plate PEFC freeze performance and the causes of any performance decay. Alternative cell materials were evaluated for their freeze performance. Freeze-thaw cycling was also performed to determine micro-porous plate PEFC survivability. Data from these experiments has formed the basis for continuing development of advanced materials capable of supporting DOEs cold-start and durability objectives.