PREPARATION AND EVALUATION OF PTFE-BONDED POROUS GAS-DIFFUSION CARBON ELECTRODES USED IN PHOSPHORIC-ACID FUEL-CELL APPLICATIONS

This paper describes the preparation and evaluation of polytetrafluoroethylene-bonded gas diffusion porous carbon electrodes. The porous carbon electrodes of size 200 cm(2) (20 cm x 10 cm) were prepared using a rolling technique and characterized by employing porosimetry, energy dispersive X-ray and scanning electron microscopy techniques. These carbon electrodes were also evaluated as individual electrodes (H-2/O-2) using a specially designed and fabricated half cell assembly as well as as complete Monocells with H-2-O-2 and H-2-air at a temperature of 175-180 degrees C and 1 atm pressure. The current density values achieved for different carbon electrodes ranged from 600 to 750 mA cm(-2) with H-2-O-2 and from 250 to 275 mA cm(-2) with H-2-air at 0.5 V, 175 degrees C and 1 atm pressure. Four phosphoric acid fuel cell monocells were tested continuously (24 h day(-1)) for 600 h (without applying an acid management system) at 175 degrees C and 1 atm pressure to study their stability. The results of long-term testing of the monocelIs revealed that all the cells were operated successfully with minimum degradation (similar to 10 mV per 600 h).