High Proton Conduction Behavior of a Water-Stable Cadmium Organic Framework and Its Polymer Composite Membranes

Abstract

A water-stable metal-organic framework material of [Cd2 (pbdc)(H2O)3](1) has been synthesized based on H4pbdc (H4pbdc = 5-phosphonobenzene-1,3-dicarboxylic acid) ligands and Cd2+ ions. The Cd2+ ions are interacted with phosphonate and carboxylate groups to form infinitely extending one-dimensional chains, which are then bridged by pbdc ligands to generate a three-dimensional structure. AC impedance study found that the proton conductivity of compound 1 is 2.32 × 10−4 S·cm−1 at 333 K and 98% RH. Many MOF-polymer composite materials have excellent properties (such as heat resistance, high proton conductivity, etc.) and can be used in fuel cells and other fields. Thus, compound 1 was added to the CS matrix to prepare a series of composite membrane 1@CS-X (X = 1%, 3%, 5%, and 7% wt), which have good thermal stability and high proton conductivity. Under the same conditions, the effects of the 1@CS-X composite membranes on proton conduction are better than that of 1, which is caused by the hydrogen bond network constructed between CS and 1, and that provides a continuous channel for proton transfer. Strikingly, the proton conduction value of 1@CS-3 reached 1.10 × 10−2 S·cm −1 353 K and 98% RH, which is much better than many recently reported MOF-polymer composites.