Simple catalyst bed sizing of a NaBH4 hydrogen generator with fast startup for small unmanned aerial vehicles

Abstract

A flow-type hydrogen generator with cobalt- and phosphorus-coated nickel foam catalyst was evaluated for a 500 W PEM fuel cell. Hydrogen was produced by catalytic hydrolysis of sodium borohydride. Startup characteristics and adequate catalyst bed sizing were considered in developing the hydrogen generator, tailored especially to small UAV applications. Gradual increase of the liquid fuel flow rate expedited the startup time to less than 5 min at 20 degrees C, which is practical for flight preparation. The effect of the cross-section on maximum hydrogen generation rates was investigated as preliminary input for catalyst bed sizing. Final dimensions of the 500 W-scale hydrogen generator were determined and validated using the space time concept. Endurance and restart characteristics were tested over two 2-h operating sessions with a 2-h rest in-between. The startup time was 2.5 min for both operations. The hydrogen generation efficiency decreased from 94% in the first operation to 81.6% in the second operation because of borate precipitation on the catalyst surface.