Intercalation of Lamellar Mineral Kaolinite with 2-Picolinic Acid: Facile Preparation, Crystal Structure Optimization, and Proton Conductivity

Graphical An anhydrous proton conductor is achieved by inserting 2-picolinic acid into the layer space of kaolinite, and the proton transport in this intercalated hybrid material is mainly through the vehicle mechanism owing to the absence of a dense H-bond network. Kaolinite intercalated with 2-picolinic acid was prepared and characterized by scanning electron microscopy, powder X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis. The proton conductivity ( σ ) of the material is 1.85 × 10 –10 S cm –1 at 353 K and gradually increases to 1.7 × 10 –7 S cm –1 at 393 K under N 2 (anhydrous environment) with an activation energy of E a = 1.93 eV, whereas σ = 1.56 × 10 –7 S cm –1 under 80 % relative humidity at 353 K with E a = 0.91 eV. The crystal structure optimized with the Cambridge Sequential Total Energy Package discloses the absence of a dense H-bond network in the layer space of kaolinite, which explains the low proton conductivity and high proton transfer activation energy of the intercalated proton conductor.