FABRICATION AND CHARACTERIZATION OF THE GRAPHITE BIPOLAR PLATES USED IN A 0.25 KW PAFC STACK

The graphite bi-polar plates were fabricated using lamination techniqu e with polyether sulfone (PES) films (50 mu m) and graphite foils (400 mu m) in between the two porous graphite plates (CBC) by keeping in a specially designed and fabricated fixture with stainless steel plates at the top and bottom. The fixture was then kept in an hydraulic hot press, at loads of 10-20 tons, and heat treated at 410 degrees C for 3 0 min. Then these graphite plates were sized to 30 cm x 20 cm x 0.64 c m, leaving 0.4 mm thick graphite foil at the centre of the plate, to a void the intermixing of the hydrogen and oxygen/air. While, the gas pe rmeability (cm(2)/sec) of the plates was determined, with N-2 gas usin g differential pressure method, their electrical resistivity (m Ohm m) was measured using milliohmmeter and passing DC current to the graphi te plates, at loads from 1-5 kgs. The values of permeability and elect rical resistivity of the plates are found to be lower than 0.01 cm(2)/ sec and 4-14 m Ohm m respectively. A stack with 6 cells was assembled using the in house developed graphite bi-polar plates, anodes and cath odes with matrix, to generate a DC power of 0.25 kW (3.6 V x 71.0 amps ). It was operated for 300 h successfully using H-2 and Air, 1 bar, at 175 degrees C. In this paper, the detailed Fabrication method of grap hite bi-polar plates and their characteristics of gas permeability, el ectrical resistivity and the results of the 0.25 kW PAFC stack operati on are presented. (C) 1998 International Association for Hydrogen Ener gy.