Fabrication of polymer electrolyte fuel cell (PEFC) H-2 sensors

Galvanic cell-type PEFC (polymer electrolyte fuel cell) gas sensors have been fabricated Their sensing behaviors to H-2 are examined. The sensing elements, Pt/Nafion composite electrodes, are prepared by first ion exchanging Pt(NH3)(4)(2+) ions and then chemical reduction with NaBH4 solution. Among the preparation variables for the composite electrodes, the NaBH4 solution flux has the most significant effect on the microstructure of the Pt deposits and therefore on the sensing characteristics of the resulting sensors. Submicron-sized Pt deposits are dispersed evenly in the deeper region of the membrane surface under a high-flux condition, while densely clustered Pt particles are deposited mainly on the external surface of the membrane when the flux is low. The current intensities are well correlated with the effective surface area of the Pt deposits, but not with the layer thickness. The current intensities and linearly responding H-2 concentration range are also influenced by the size of the capillary-type diffusion barrier.