Preparation And Performance Of Novel Polyphosphazene Membrane Carrying Cryptoether Units For Alkaline Fuel Cell

With the increasing severity of energy and environmental issues,developing new energy supply technologies is often mentioned as a key to solve these issues.Anion exchange membrane fuel cell as the most promising clean and efficient power generation technologies have attracted much considerable attention.Alkaline anion exchange membrane fuel cells(AAEMFCs)have shown remarkable performance due to their unique properties,such as the enhanced electrochemical kinetics and the use of inexpensive non-precious metal electro-catalysts.Anion exchange membrane as the key unit of AAEMFCs face challenges such as poor alkali stability and low ion conductivity.For the purpose to enhance the alkali stability of the membrane and increase the ionic conductivity of the membrane,suitable polymer backbones and cationic groups should be found.Polyphosphazene skeleton,which has a high density of loaded cations is easily modified by chemistry.Moreover,the role of cryptand group in strongly complexing with metal cations has been demonstrated.Here,we show that the introduction of HDME and PADE,which are used to form the three new kind of polyphosphazene anion exchange membrane.At the same time,we explored their various properties.1.The first anion exchange membrane PHDME-POH-x with HDME as the loading group and polyhalophosphazene as the polymer skeleton were synthesized by Williamson synthesis.The ion exchange capacity of PHDME-POH-40 grafted with 40%HDME was 1.64 mmol/g at 25?,the corresponding water absorption,swelling ratios,and the ion conductivity at 80? were respectively 134.7%,81.4%and 43.6mS·cm-1.It was found that this new anion exchange membrane's conductivity and ion exchange capacity did not change substantially when soak it in 2M KOH solution 10OOh,indicating that it had good alkali stability.2.Similar to the previous PHDME-POH-x,the second anion exchange membrane PPADE-POH-x was synthesized in the same manner.The only difference between the two membranes is that PADE acts as a load group.When grafted HDME ratio is 40%,the ion exchange capacity of PPADE-POH-x was 1.43mmol/g at 25?,the corresponding water absorption and swilling ratios is 110.6%and 76.3%.Also,the ion conductivity at 80? is 44.9 mS cm-1.In the same way,we immerse PPADE-POH-x in the KOH solution of 2M for 1OOOh,its conductivity and ion exchange capacity are basically unchanged,which indicates that it had good alkali stability.3.With the purpose to improve the mechanical properties of anion exchange membrane,a series of PHDME-PVA composite membranes were obtained by blending HDME-loaded polyphosphazene polymer with PVA and crosslinking with glutaraldehyde.Consequently,the optimal proportion of PHDME in the system is 40%,resulted in a significant overall performance.In this case,the ion conductivity of PHDME-PVA at 80? was 80.2 mS cm-1.Furthermore,long-term conductivity and ion exchange capacity stability of PHDME-PVA for 1O00h,under continuous soaking at 2M KOH solution has also been achieved.This revealed the good alkali stability of this new membrane.