Design and development of proton exchange membrane (PEM) from synthetic rubber and carbon nanoballs for PEM fuel cell

Abstract

The need for an alternative source of energy is very urgent. The challenges are to develop a new technology that will produce an efficient and environmentally friendly source of energy other than fossil fuel. A fuel cell system especially proton exchange membrane fuel cell is considered the most promising alternative method of converting and exploiting energy with many benefits including low pollutant emission, sustainability and reliability. However, a number of issues need to be resolved before the proton electron membrane fuel can become commercially and technologically viable. These include the durability and the availability of the membrane among many other factors. In this research, Proton Exchange Membrane (PEM) was synthesized by sulphonation of polystyrene butadiene rubber that is readily available in South Africa, using chlorosulphonic acid as the sulphonating agent. The synthesized membrane was blended with carbon nanoballs (CNBs) produced by the swirled floating catalytic chemical fluid deposition (SFCCVD) method designed and conceptualized by Iyuke (2005). Synthesis of carbon nanoparticles with this reactor was optimized using different experimental conditions of pyrolysis temperature, flow rates of acetylene, hydrogen and argon gases. A maximum production rate of 0.35 g/min was obtained at 1000oC, acetylene flow rate of 370 ml/min, hydrogen flow rate of 180 ml/min and a flow ratio of acetylene to hydrogen equal to five. Since clean nanoparticles are required in this work for membrane synthesis, the SFCCVD reactor was modified to synthesize clean carbon nanoballs via a non-catalytic method. The carbon nanoballs produced were used in the formulation of sulphonated polystyrene butadiene rubber–carbon nanoballs composite membrane. The synthesised membranes and the composite membranes were characterized to determine the ion exchange capacity, degree of sulphonation, thermal stability, water uptake, vi porosity, proton conductivity, solvent uptake, and morphology and methanol crossover. The characterization of the synthesized membrane for methanol cross over is to determine the suitability of the membrane for possible application in direct methanol fuel cell; however hydrogen fuel is used in this work. The results obtained revealed that the blending of the membrane with CNBs improved the thermal stability, water uptake, porosity, solvent uptake, methanol crossover and proton conductivity of the membrane with more than 50 % increase in proton conductivity. The results of various analyses conducted on the synthesized membrane revealed that the synthesized membrane shows better qualities in terms of thermal stability, solvent uptake, porosity to solvent, methanol crossover and water uptake than Nafion 112, which is the commercially available membrane. The synthesized and composite membranes were sandwiched between two electrodes to produce a membrane electrode assembly (MEA), using the hot press method at constant temperature, pressure and time. The performance of the fabricated MEA was tested in a single PEM fuel cell using hydrogen as the fuel gas and oxygen as oxidant at room temperature (about 25oC). The results obtained revealed that the utilization of sulphonated PSBR resulted in higher performance compared to Nafion 112. Nafion 112 produces a maximum power density of 67 mW/cm2 while the membrane synthesized from PSBR generated a maximum power density of 74 mW/cm2. This difference is corresponding to about 10% increment. Also the membrane blended with CNBs exhibited a superior performance to a non-blended membrane. The former gives a maximum power density in the range of 74-97 mW/cm2 depending on the mass of CNBs. These values are about 7-32 % higher than the nonblended membrane.