The Preparation And Performance Characterization Of Well-ordered Sulfonated Silica Electrolyte

Proton exchange membrane fuel cells(PEMFCs)operating at high temperature have attracted considerable attention in recent years because they could benefit from enhanced tolerance of catalyst to carbon monoxide gas, increased electrochemical reaction kinetics rate at both cathode and anode and improved water and heat management. Because the perfluorosulfonic acid(PFSA)polymeric membranes have robust structure and excellent proton conductivity in the hydrated state,so they often used PEMs for current PEMFC technology, for instance Nafion membranes. However,the drastic decrease in proton conductivity at high temperature and low relative humidity can lead to performance degradation of fuel cells. Therefore, the research of proton exchange membrane material with high protons conductivity and high thermal stability at high temperature and low humidity environment is one of the technical challenges in fuel cell development. Periodic ordered sulphonated-silica nanoelectrolytes with 2D hexagonal(2D-H)structure,3D cubic bicontinuous (3D-CB)structure,3D face-centered cubic(3D-FC)structure and 3D body-centered cubic (3D-BC) structure were synthesized through a multiphase hydrogen bond self-assembly between the charged silica,3-mercaptopropyltrimethoxysilane and triblock copolymer. The increase in proton conductivity at high temperature can achieve the requirements of proton exchange membrane fuel cells(PEMFCs)operating at high temperature.In addition,the performance of methanol resistance were studied in this paper. The conclusions have been drawn as following:(1)The mesoporous silica with 2D hexagonal (2D-H)structure,3D cubic bicontinuous(3D-CB)structure,3D face-centered cubic(3D-FC)structure and 3D body-centered cubic (3D-BC) structure were synthesized through a multiphase hydrogen bond self-assembly between the charged silica and triblock copolymer.They have uniform nanoarrays with long-range order and a narrow pore size distribution. The thermal analysis results show that they have good thermal stability.(2) Small angle XRD and high resolution TEM results exhibit uniform nanoarrays with long-range order of the sulphonated-silica nanoelectrolytes. The well-ordered structure demonstrated a facile proton transport pathway of the electrolyte to improve proton conductivity. AC impedance spectroscopy analysis show that the conductivity of the sulphonated-2D-H electrolyte, sulphonated-3D-CB electrolyte, sulphonated-3D-FC electrolyte and sulphonated-3D-BC electrolyte reached to 0.270S/cm,0.242 S/cm,0.226S/cm and 0.188 S/cm,at elevated temperature of 200℃.(3) The low swelling and phase transformation of methanol at the elevated temperature also make low fuel crossover through the sulphonated-silica electrolyte. At elevated temperature from 120-200℃, the limiting methanol permeation current densities decreased dramatically to 0.1-0.5mA/cm2,resulting in an improved relative selectivity of 66.02-91.74. The high proton conductivity and low methanol crossover of the sulphonated-silica electrolyte at elevated temperature demonstrate great potential as high-temperature electrolyte membranes for direct methanol fuel cells.