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The gas diffusion layer (GDL) plus separator in the polymer electrolyte fuel cell contributes more than 1/3 to the stack cost, even at the mass production stage. Therefore, we have taken on the challenge to develop a new, integrated concept for these crucial components, based on intelligent application of low-cost technologies and, most importantly, uniform transport of reactant and product over the whole catalyst layer via forced cross-flow between neighboring interdigitated channels formed in the GDL. This new design concept promises to significantly lower cost, as well as improving performance and durability. Specifically, the design incorporates a corrosion-resistant flat-metal separator (FMS) with a thin carbon/resin coating, and a low-cost GDL, consisting of short carbon fibers (CFs) bonded with resin, forming gas-flow channels whose manufacture should be compatible with mass-production. At the optimized FMS + GDL, we have achieved 5.7 m /cm 2 contact-resistance and complete immunity to corrosion over 4,000 h in 0.1 M H 2 SO 4 solution at 90°C. By combining various CFs and resins, the gas-diffusivity, electrical resistance and mechanical strength have been balanced and are sufficient for GDL application. A limiting current of 3.3 A/cm 2 in a single cell has been achieved under pure H 2 and140 kPa air at 80°C.

A heat exchanger for a totally implantable heat driven LVAD is an essential element in overall system thermal management. The heat exchange is accomplished by supplying cooling water from a pusher-plate driven water pump to the engine and then to the heat exchanger on the pump housing. The temperature of the interface between the blood and pump surface is of critical importance for clinically acceptable operation of the system. Temperatures were measured by instrumenting a pump housing with thermocouples and an electric heater on a mock circulatory loop. Flows were varied from 1 to 8 l/min and heat input was 20 watts. At 1.0 l/min pump flow the maximum inner surface temperature rise is 4.5 degrees C. In vitro tests were conducted to examine the effect of elevated temperature on platelete function. Both platelet aggregation and adhesion were reduced at elevated temperatures of 42 and 47 degrees C indicating a potential benefit of reduced thrombogenesis on the heated housing surface.

A new design concept for polymer electrolyte fuel cells, which included a flat-metal separator and a gas diffusion layer (GDL) with interdigitated gas flow channels (FCs), was developed in our previous research. This design led to improved performance compared to that obtained with the conventional design of a metal separator with FCs and a flat GDL. Applications of the interdigitated gas flow channels formed on the separator, however, have conventionally faced two issues associated with low performance: one occurs under high humidity conditions because of nonuniform gas flow due to accumulated water in the GDL and the other is caused by forced water discharge from the GDL under low humidity conditions. In this study, both conventional and new cell designs were tested with single cells of 1 cm2 active area, and the performances were compared at high and low humidity with various conditions of gas supply. From these results, we have found that the new design of the GDL with interdigitated channels has a clear advantage over the conventional interdigitated cell in being able to maintain high performance under conditions of both water excess and water shortage.

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