The Synthesis of Proton Conducting Membranes from Polystyrene Butadiene Rubber for Fuel Cell Application: The Effect of Sulphonating Agents on the Membrane Characteristics

Abstract

Out of the three major components (membrane, electrocatalyst, and bipolar plates) of proton exchange membrane fuel cell, the cost of the polymer electrolyte membrane is the highest. Therefore, reduction in cost of the membrane will help in reducing the cost of the fuel cell. This work aims at investigating the effect of sulphonating agents (sulphuric acid, acetyl sulphate, and chlorosulphonic acid) on the quality of the membranes synthesized from polystyrene butadiene rubber, which is locally available in South Africa for fuel cell application. The synthesized membranes are characterized by its ion exchange capacity, degree of sulphonation, morphology, thermal stability, and proton conductivity. Analysis of the results obtained reveal that sulphonation with chlorosulphonic acid yields a good membrane with degree of sulphonation in the range of 5.52–31.11%. The synthesized membranes in their fully hydrated form have proton conductivities in the range of 10⁻³–10⁻² S/cm, which increases with increase in temperature. The results of the thermal stability revealed that membranes synthesized with chlorosulphonic acid are thermally stable up to 320°C, which is suitable for the high operating temperature fuel cell. Results of the electrochemical performance of the synthesized membrane in a single fuel cell stack further revealed that the membrane synthesized with chlorosulphonic acid shows better performance (maximum power density of 41.94 mW/cm²) than the membrane synthesized with acetylsulphate (maximum power density of 11.86 mW/cm²).

Keywords:

• degree of sulphonation
• polystyrene butadiene rubber
• proton conductivity and fuel cell
• sulphonating agents
• thermal stability