Quaternized Polyethersulfone Anion Exchange Hybrid Membranes With Mg（OH）₂ Nanoparticles

Alkaline anion exchange membrane fuel cell (AAEMFC) is regarded as one kind of clean and efficient power source, which has the advantages of higher reaction kinetics, non-noble metal catalysts, and low fuel permeability. But it cannot be applied to industrial production because of the low conductivity of alkaline exchange membrane. Therefore, promoting the performance of the alkaline anion exchange membrane is a research hotspot of AAEMFC technology. In this work, the nanoparticles of magnesium hydroxide were added in the PES-ImCl to improve the ion conductivity. Because of the special morphologies and electrically charged characteristic, magnesium hydroxide would induce ion clusters aggregate to form ions channels, which had positive effect on conductivity of alkaline exchange membrane.Firstly, applying microemulsion method and hydrothermal method, two kinds of morphologies of magnesium hydroxide nanoparticles were prepared. Then morphologies and sizes of two specific nanoparticles were investigated by transmission electron microscope (TEM). The diameter of the lamellate magnesium hydroxide (l-Mg(OH)2) prepared by microemulsion method was about 100nm. While for magnesium hydroxide (r-Mg(OH)2) prepared by direct hydrothermal method, the length and diameter of the rod was about 45nm and 20nm, respectively. Also, XRD patterns demonstrated that both l-Mg(OH)2 and r-Mg(OH)2 were hexagonal structure.Furthermore, the CMPES was synthesized successfully with the reaction of PES, concentrated sulphuric acid and chloromethyl octyl ether (CMOE). And the introduction of CH2C1 structure in CMPES was proved by 1H-NMR spectrum. Subsequently, through the reaction of CMPES and 1-methylimidazole, imidazolium-functionalized PES (PES-ImCl)were synthesized. Finally, PES-ImCl was dissolve in N-methylpyrrolidone (NMP) and then amount of r-Mg(OH)2 were added to prepare PES-ImOH/r-Mg(OH)2 membranes by the casting method. Based on the results of experiments, it is conclued that the PES-ImOH/r-Mg(OH)2 membranes possess higher hydroxide conductivity when the polymer concentration is 10% and ultrasonic power is 800W.In order to investigate the influence of the morphologies of Mg(OH)2 on the hybrid membranes, PES-ImOH/l-Mg(OH)2 membranes and PES-ImOH/r-Mg(OH)2 membranes were prepared with different additions of l-Mg(OH)2 and r-Mg(OH)2, respectively. According to experiments, the water uptake and the swelling ratio of the two kinds of hybrid membranes are at the same level. When the temperature is 60℃, the water uptake and swelling ratio of all the hybrid membranes is about 70% and 30%, respectively, which proves the excellent dimensional stability of the hybrid membranes. Besides, for the two kinds of hybrid membranes, the highest conductivities of membranes are obtained at the nanoparticles addition of 1%. At 60℃, the hydroxide conductivities of PES-ImOH/1% r-Mg(OH)2 membrane and PES-ImOH/1% l-Mg(OH)2 membrane are 24.3mS cm-1 and 24.7mS cm-1 respectively, which are 33% and 35% higher than the PES-ImOH membrane. Also, it should be noted that the tensile strength of PES-ImOH/γ-Mg(OH)2 membranes is a little lower than PES-ImOH membrane, when the increase of addition of r-Mg(OH)2. However, the tensile strength of PES-ImOH/1%γ-Mg(OH)2 membrane is 11.2MPa, which is the highest one.