Preparation And Characterization Of High Temperature Proton Exchange Membranes Based On Hyperbranched Polyamidoamide Crosslinked Blended Polymers

The fuel cell is an electrochemical energy conversion device with high current density,high energy density and high conversion efficiency.Among various types of fuel cells,proton exchange membrane fuel cells use proton exchange membranes(PEMs)as the electrolyte.Nowadays,the main problem to PEMs is how to achieve a superior proton conductivity without deteriorating the mechanical property of the membranes.The blended polymers of polyvinyl chloride(PVC)and polyvinylpyrrolidone(PVP)were employed as the membrane materials to prepareg the membranes of the PEMs.Hyperbranched polyamidoamines(HP)was prepared and explored to be used in high temperature PEMs.In addition,porous polytetrafluoroethylene(PTFE)was introduced into the PEMs for reasonable mechanical properties.Firstly,different ratios of PVC and PVP were mixed to cast blended membranes.The influences of the ratios of PVC to PVP on the properties of the blended membranes were investigated.The results indicate that the higher content of PVC,the better mechanical properties of the membrane;In addition,the more introduced PVP would result in,increased conductivity of the PEMs.Synthesis of HP was made according to the reference and it was then added into the PVCPVP solutions to prepare membranes for high acid doping levels.A series of membranes were fabricated by altering the mass ratio of PVP to HP with a certain mass ratio of PVC as 60%.As a result,HP exhibited a higher acid absorption ability than PVP,which can improve the conductivity of the membranes.However,the mechanical properties of the obtained membranes decreased with the addition of HP.In order to improve the mechanical properties of the membrane,commercial porous PTFE was introduced to reduce the plasticization effect of the doped phosphoric acids(PA)for acceptable mechanical strength of the composite membranes.Polymers of PVC and PVP were first blended and then the blended polymers were crosslinked by HP via the SN2 nucleophilic substitution reaction.The porous PTFE membrane was used as the framework to further enhance the strength of the composite membranes.As a result,the PA doped PTFE reinforced composite membranes containing 29 wt%of the HP exhibited a high proton conductivity of 0.154 S cm-1 at 160℃ without humidifying,and an excellent tensile stress at break of 22 MPa under ambient atmosphere.These results are,much better than the PA doped pristine PVP-PVC composite membranes.A single H2/O2 fuel-cell demonstrated that a peak power density of 233 mW cm-2 was achieved at 180℃ by using the fabricated composite membrane as the electrolyte with no humidification.