Preparation and characterization of zirconium (1,3,5,2λ5,4λ5,6λ5-triazatriphosphinine-2,2,4,4,6,6-hexyl) hexa(phosphate) as a novel high-temperature proton conductor

Abstract

Zirconium (1,3,5,2λ5,4λ5,6λ5-triazatriphosphinine-2,2,4,4,6,6-hexyl) hexa(phosphate) (ZrTHPA) is synthesized by chelation combination (1,3,5,2λ5,4λ5,6λ5-triazatriphosphinine-2,2,4,4,6,6-hexyl) hexa(phosphonic acid) (THPA) with zirconium ion in a certain ratio. The THPA is synthesized by hexachlorocyclotriphosphazene with P(OEt)3, and hydrolyzed in HCl. Their structure is characterized by nuclear magnetic resonance (NMR) and infrared spectroscopy (IR), and hydrogen bonding and chelation interactions between Zr4+ and phosphonic acid are detected. X-ray diffraction and scanning electron microscopy (SEM) show that ZrTHPA has a layered structure. Thermogravimetry-differential thermal analysis (TG-DTA) shows that ZrTHPA has good thermal stability. ZrTHPA also has good oxidative stability and hydrolysis resistance. The ion exchange capacity of ZrTHPA (1:2) is 2.21 meq g−1. At 180 °C, the proton conductivity of ZrTHPA (1:2) at 100%, 50%, and 0 relative humidity is 0.128 S cm−1, 0.069 S cm−1, and 0.038 S cm−1, respectively. ZrTHPA can be used as solid acid catalyst or proton conductor which is doped into proton exchange membranes.