A 3D open-framework iron hydrogenophosphate showing high proton conductance under water and aqua-ammonia vapor

Abstract

Herein we report the first example of the proton conductivity of an open-framework metal phosphate (NH₃(CH₂)₃NH₃)₂–[Fe₄(OH)₃(HPO₄)₂(PO₄)₃]·4H₂O under aqua-ammonia vapor. Its optimized proton conductivity is 5 × 10⁻² S cm⁻¹ at 313 K and aqua-ammonium vapor from 1 M NH₃·H₂O solution. That is approximately two orders of magnitude greater than the maximum value under water vapor (8.0 × 10⁻⁴ S cm⁻¹ at 317 K and 99% RH). The proton transfer mechanism has been proposed in terms of the structural analyses, activation energy calculations, and PXRD determinations.