Adiabatic fuel cell stacks have attracted industry attention for their simple design, low cost, and reliability. Operating at near-ambient pressure, their efficiency and net power density make them competitive with more complex pressurized systems. In the last year Los Alamos’ patent rights to this technology have been made available for outside licensing through the Laboratory’s Technology Transfer Division.

The simplicity of adiabatic stacks is their most attractive feature and is accomplished primarily through two technological elements. First is the direct humidification of the fuel cell membrane electrode assemblies (MEAs) with liquid water, and the second is operation of the fuel cell stack at very-near-ambient pressure.

Direct MEA humidification is made possible through the introduction of an anode-wicking backing that conveys liquid water from the anode flow-field plenum through the nominally hydrophobic gas diffusion layer directly to the membrane throughout the active area.

Because even modest pressure can result in high compression power requirements, near-ambient pressure operation is critical to the stack’s efficiency. In conventional systems humidification modules, internal manifolding, and two-phase flows in the cathode channels create high-pressure drops that necessitate air inlet pressurization, but the direct humidification system avoids these pressure drops and allows the inlet pressure to be kept to about six inches of water.

During the normal operation of this well-humidified fuel cell stack with a dry, ambient temperature cathode air inlet, the airstream becomes heated and saturated with water vapor as it passes through the cells. This effect provides in situ evaporative cooling of the stack, eliminating the need for separate cooling systems or in-stack cooling plates. The non-isothermal stack operation and evaporative cooling result in an “adiabatic” stack.

The simplicity of the adiabatic system is easy to appreciate when compared to the conventional system, with its extensive flow and control elements.

A simple plastic condenser is used to recover surplus water and works effectively even in Los Alamos’ high desert climate. The single-step heat exchange process allows higher temperature differentials in the condenser than could be attained in a radiator, and may prove to be a general improvement over more conventional approaches using radiators and coolants.

Point of Contact
fuelcells@lanl.gov