Synthesis And Characterization Of Polystyrene-based Solid Electrolyte Membrane For Fuel Cells

Polymer electrolyte membranes, kind of Solid polymer electrolyte (SPE), play an important role to separate fuel and oxidizer, conduct ion and insulate electronics in fuel cells. Alkaline polymer electrolyte membrane fuel cells (APEMFC) have become an important research direction of fuel cell development. Compared with proton exchange membrane fuel cells (PEMFC), APEMFC have many advantages such as lower cost, simpler battery systems and faster oxidant reduction kinetics. Therefore APEMFC have recently drawn wide attention. However, the ionic conductivity of alkaline polymer electrolyte membrane is less than proton exchange membrane because OH- has a larger volume and less activity than that of H+. So the preparation of alkaline polymer electrolyte membrane with high ionic conductivity is valuable theoretically and practically in development of APEMFC.Polystyrene (PS) as a common starting material for ion exchange resins has low cost, designable molecules and good chemical stability, so it is an ideal basic polymer of alkaline polymer electrolyte membrane. But its poor processability and low ionic conductivity are the key factors that hindered its application in fuel cells. In this paper, alkaline polymer electrolyte precursor was prepared by introducing methyl methacrylate (MMA) and butyl acrylate (BA) to the main chain of Styrene and 4-chloromethylstyrene copolymer. Alkaline polymer electrolyte membrane was further prepared by quaternization reaction and anion exchange. The structure and properties were also characterized and analyzed. Finally the membrane electrode was prepared using the obtained membrane and its performance was tested. The main conclusions of the work are summarized as follows: (1) Styrene and 4-chloromethylstyrene copolymer was synthesized using different ratios ofstyrene (St) and 4-chloromethylstyrene (CMS) by free radical copolymerization. With the increase content of CMS, the mole fraction of CMS unit in the copolymer increased. The mole fraction of CMS unit was consistent with the feed ratio.(2) By using molecular design method, MMA and BA were incorporated as the flexible units to improve the mechanical properties of the copolymer. When the molar ratio of St, CMS, MMA and BA was 25:10:25:40, the resulting polymer shows satisfying properties.(3) Alkaline polymer electrolyte membrane was prepared by quaternization reaction and anion exchange. The water content of the membrane was increased after the quaternization reaction. The conductivity of the membrane was up to 3.07×10-3 S/cm at room temperature and the ion exchange capacity (IEC) was 0.81mmol/g. The strength of resulting membrane was 17.40MPa under dry state and 7.39MPa under wet state.(4) The conductivity of resulting membrane increases with the temperature. The relationship between conductivity and temperature followed the Arrhenius principle.(5) Membrane electrode assembly (MEA) was prepared using the obtained membrane, and then the electrochemical performance of the obtained membrane was measured using a single cell station. The fuel cell's maximum power density was 27.12mW/cm2, the maximum current density was 157.3mA/cm2, and the open circuit voltage was 1.06V. The membrane was expected to be used in fuel cell and had good performance.