PROTON EXCHANGE MEMBRANE FUEL CELL; EMPIRICAL REVIEW ON THE DEGREE OF SULPHONATION

Empirical review on the degree of sulphonation of polymeric materials for proton exchange membrane fuel cell (PEMFC) was carried out. Fuel cell generally applies the principle of electrochemistry in which chemical energy is converted directly into electrical energy. Amongst the league of fuel cells, the proton exchange membrane fuel cell is the most promising. However, the central component of PEMFC is the ionic polymer membrane that must be rendered conductive. This study showed that the measure of sulphonation is pivotal in achieving conductivity of the polymer for fuel cell application. The study revealed that for an optimum conductivity to be achieved, optimum degree of sulphonation (DS) is needed. The recognized factors that affect the optimum degree of sulphonation were the type of sulphonating agent (as chlorosulponic acid achieved 39.04% and 50.21% differential increment over both sulphuric acid and fuming sulphuric acid, respectively), sulphur content (while the lowest Sc of 1.76% achieved 9.13% DS, the highest Sc achieved 20.04% DS), optimum acid concentration (as DS of 20.04 % was achieved with 1.6 mmol/g as against 2.0 mmol/g of 16.76 %), nature of the polymer base material (as more –SO3H groups attached to aliphatic polymers than aromatic), optimum time and stirring speed, optimum temperature, and optimum weight of the base polymer. The study was able to unravel that the degree of sulphonation can be determined via elemental sulphur analysis either by analytical or titrimetric method. The study also showed that the degree of sulphonation can be predicted correctly using a predictive model.