The proton conduction behavior of two 1D open-framework metal phosphates with similar crystal structures and different hydrogen bond networks

• Published in: RSC advances 2023-04, Vol.13 (19), p.1273-12711
• Main Authors: Zhang, Kai-ming, Ji, Min-fang, Zhou, Xue-Yi, Xuan, Fang, Duan, Bo-yuan, Yuan, Yuan, Liu, Guang-xiang, Duan, Hai-bao, Zhao, Hai-rong
• Format: Article
• Language: English
• Subjects: Chemical synthesis; Chemistry; Crystal structure; Diamines; Hydrogen bonds; Hydrothermal reactions; Propylene; Proton conduction; Protons; Thermogravimetric analysis; X ray powder diffraction; Zinc phosphate
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/d3ra01130e

Two open-framework zinc phosphates [C 3 N 2 H 12 ][Zn(HPO 4 ) 2 ] ( 1 ) and [C 6 N 4 H 22 ] 0.5 [Zn(HPO 4 ) 2 ] ( 2 ) were synthesized via hydrothermal reaction and characterized by powder X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. Both compounds have a similar crystal structure and macroscopic morphology. However, the difference in equilibrium cations, in which the propylene diamine is for 1 and the triethylenetetramine is for 2 , results in a significant distinction in the dense hydrogen grid. The diprotonated propylene diamine molecule in 1 is more favorable for forming a hydrogen-bond network in three dimensions than in 2 , in which the twisted triethylenetetramine forms a hydrogen bond grid with the inorganic framework only in two dimensions owing to its large steric effect. This distinction further leads to a disparity in the proton conductivity of both compounds. The proton conductivity of 1 can reach 1.00 × 10 −3 S cm −1 under ambient conditions (303 K and 75% RH) and then increase to 1.11 × 10 −2 S cm −1 at 333 K and 99% RH, which is the highest value among the open-framework metal phosphate proton conductors operated in the same conduction. In contrast, the proton conductivity of 2 is four orders of magnitude smaller than 1 at 303 K and 75% RH and two orders smaller than 1 at 333 K and 99% RH. The difference in equilibrium cations of the two compounds results in a big distinction in the dense hydrogen grid. This distinction further leads to the disparity in the proton conductivity of both compounds.