To provide a fuel cell system for low-voltage portable power applications Los Alamos researchers have developed simple, reliable, “air-breathing” fuel cell stacks. They operate without peripheral fans for cooling or reactant flow, or the attendant electronics and controls, effectively avoiding the need for active humidification, active cooling, or cathode air pressurization.

Air-breathing stacks have already been used in flashlights, remote-controlled cars, and laptop computers, and will power a new scooter that is currently under development.

The Technology
The air-breathing stacks are stable and self-regulating, relying on diffusion-limited oxygen access to maintain a positive water balance in the cells. Oxygen in the air is allowed to diffuse into the stack from the periphery of the flow-field plates (the source of the stacks’ name,) as water diffuses out. The water produced serves as a necessary hydrant to the polymer electrolyte membrane while the surplus is lost through evaporation.

The configuration of the stack is based on circular flow-field plates and an annular hydrogen feed manifold, which are anchored by a single tie-bolt extending through the stack’s central axis.

“Air-Breather” Fuel cell Stack Configuration

With this geometry, the hydrogen flows out from the central manifold while the oxygen diffuses inward from the periphery. The result is a system that allows for efficient cooling through conduction, maximized air access, and minimized diffusion path lengths for both hydrogen and oxygen.

The system’s radial symmetry provides for a simplified part fabrication process, and the single tie-bolt reduces the stack’s footprint, overall size, and weight. Fuel can be supplied from a pressurized source through a low-pressure regulator, or even a hydrogen-filled balloon.

Point of Contact
fuelcells@lanl.gov