M. Ghouse

Preparation and evaluation of PTFE-bonded porous gas diffusion carbon electrodes used in phosphoric acid fuel cell applications

Abstract This paper describes the preparation and evaluation of polytetrafluoroethylene-bonded gas diffusion porous carbon electrodes. The porous carbon electrodes of size 200 cm2 (20 cm × 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 H2-O2 and H2-air at a temperature of 175–180 °C and 1 atm pressure. The current density values achieved for different carbon electrodes ranged from 600 to 750 mA cm−2 with H2-O2 and from 250 to 275 mA cm−2 with H2-air at 0.5 V, 175 °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 °C and 1 atm pressure to study their stability. The results of long-term testing of the monocells revealed that all the cells were operated successfully with minimum degradation (~10 mV per 600 h).

Fabrication and characterisation of the graphite bi-polar plates used in a 0.25 kW PAFC stack

The graphite bi-polar plates were fabricated using lamination technique with polyether sulfone (PES) films (50 μm) and graphite foils (400 μn) 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 °C for 30 min. Then these graphite plates were sized to 30 cm × 20 cm × 0.64 cm, leaving 0.4 mm thick graphite foil at the centre of the plate, to avoid the intermixing of the hydrogen and oxygen/air. While, the gas permeability (cm2/sec) of the plates was determined, with N2 gas using differential pressure method, their electrical resistivity (mΩm) was measured using milliohmmeter and passing DC current to the graphite plates, at loads from 1–5 kgs. The values of permeability and electrical resistivity of the plates are found to be lower than 0.01 cm2/sec and 4–14 mΩm respectively. A stack with 6 cells was assembled using the in house developed graphite bi-polar plates, anodes and cathodes with matrix, to generate a DC power of 0.25 kW (3.6 V × 71.0 amps). It was operated for 300 h successfully using H2 and Air, 1 bar, at 175 °C. In this paper, the detailed fabrication method of graphite bi-polar plates and their characteristics of gas permeability, electrical resistivity and the results of the 0.25 kW PAFC stack operation are presented.