Microwatt Fuel Cell for Long-Term and Wide Ambient Temperature Range Operation

Abstract

A small microwatt fuel cell stack and system was designed, fabricated, and tested for passive operation with pure H2 and O2 to provide continuous power for multiple decades with uncontrolled fluctuating ambient conditions. The stack was designed to operate with dead ended gas flows with water removal via passive membrane diffusion to notches in the bipolar plates. Additional requirements for decades long operation is minimizing H2 and O2 consumption, specifically membrane cross-over; to minimize cross-over, stacks were built with layered membranes of 100 µm and 400 µm. The stack spatial water concentration level was monitored during operation by in situ neutron imaging to evaluate the passive water management design. Operation was verified by testing at temperatures ranging from -55 °C to 80 °C, including periodic pulses in power.

Imaging and Modeling of Passive Water Management in a Miniature Fuel Cell

“…A two-dimensional multiphysics model was developed to help elucidate water transport phenomena and inform a greater cell model. The main differences between this model and our previous work (7) are the model geometry and the inclusion of time-dependent terms in the gas transport, water transport, and heat equations to enable transient simulation. Figure 5 shows the updated model geometry.…”

“…In past work, similar assemblies of these microwatt fuel cells and their water management systems were imaged, however, only at temperatures at and above 25 ºC (7). In this work, the passive water management system in the microwatt fuel cell is further studied and shown to be successful at temperatures down to −20 ºC, but requires additional design considerations at freezing and below-freezing temperatures to prevent gas crossover.…”