Preparation Of PTFE-reinforced PFSA And SMMT/SPSU-BP Composite Membranes And Their Fuel Cell Performance

Nowadays, the proton exchange membrane fuel cell (PEMFC) technology is in the key period of turning basic research to application development. Performance, durability, and cost is some of the requirements that must be met before PEMFC can be used more extensively. As one of the key components of the PEMFC, the proton exchange membrane (PEM) has a significant effect on all three ways. The developments of new PEMs with various chemicals and physical structures are aimed at higher proton conductivity, excellent mechanical and chemical stability, and lower cost. Therefore, this subject has become a research hotspot in the field of fuel cell.The polytetrafluororthylene (PTFE) reinforced perfluorosulfonic acid (PFSA) composite membrane (SPCM) was prepared by a solution-spray process. SPCM composite membrane has evident crystal and cluster morphology. The crystalline structure of the PFSA resin mainly influences the mechanical strength of SPCM composite membrane. The PTFE porous membrane has a direct effect on the structure stability of the composite membrane.The SPCM composite membrane has Young’s modulus in the transverse direction of263.0MPa and260.0MPa under dry and wet condition, that is higher than the NR211membrane over59%and123%, respectively. The SPCM composite membrane has swelling rate of0-5.3%, that reduced6.3-9.7%relative to the NR211membrane.The SPCM composite membrane has hydrogen permeability of5.9×10-10cm3·cm·cm-2·sec-1·cmHg-1, which is half of that of the NR211membrane.To ascertain the performance of the SPCM composite membrane in PEMFC,5,000cycles of dry/wet cycling test,400hours of accelerated open circuit voltage test under low humidity, and1,000hours of load cycling test were performed.The results show that the composite membrane has excellent stability and durability of8845hours.The analysis of impedance, hydrogen crossover, and cyclic voltammogram data during the tests shows that the degradation of the PEMFC with SPCM composite membrane is mainly due to the activity degradation of the electrode catalyst. The PEMFC stack with SPCM composite membranes is evaluated. The mean single cell voltage is0.681V@800mA·cm-2, and voltagerangeability is less than±20mV. The300m2SPCM composite membrane has been used in more30PEMFC engines for tests. The research results verify that the solution-spray process is feasible for composite proton exchange membrane manufacture for PEMFC application.To get the composite membrane with higher chemical stability, the hybrid composite membrane of the CeO2-PFSA/PTFE was developed by the solution-spray process.The CeO2-PFSA/PTFE composite membrane has a uniform structure, and enhanced mechanical performance compared with the SPCM composite membrane. With Fenton reagent of20 wt.%H2O2solution containing20ppm FeSO4at90℃, the fluoride emission rate for the CeO2-PFSA/PTFE composite membrane is0.083mgF-·gmem-1·hr-1, much lower than that for the SPCM composite membrane of0.311mgF-·gmem-1·hr-1. CeO2-PFSA/PTFE composite membrane has maximum tensile strength exceeding31MPa in both transverse and machine direction and reduced anisotropy compared with the SPCM composite membrane of28.IMP in machine direction.The CeO2-PFSA/PTFE composite membrane has28%lower permeability than SPCM composite membrane. In the open circuit voltage test for400hours under low humidity, the hydrogen crossover current density of the CeO2-PFSA/PTFE composite membrane did do not change significantly. The mean single cell voltage of the PEMEC stack with CeO2-PFSA/PTFE composite membrane is0.657V@800mA·cm-2and0.623V@1000mA·cm-2. These mean that the CeO2-PFSA/PTFE composite membrane has excellent radical scavenge ability and is applicable to PEMFC.To develop low cost PEM, the sulfonated polyethylene biphenyl ether sulfone (SPSU-BP) membrane was modified by sulfonic acid montmorillonite (SMMT), and then the PTFE enhanced SMMT/SPSU-BP composite membrane was developed. The results of studies show that the composite membranes contain more20%bound water than the SPSU-BP membrane.The swelling of the composite membrane in water at90℃reduce to15.0%from56.8%, and the mechanical stability is enhanced obviously. The fuel cell with the SMMT/SPSU-BP/PTFE composite membrane has stable performance under high temperature and low humidity condition.