H/F‐Substitution‐Induced Homochirality for Designing High‐T_c Molecular Perovskite Ferroelectrics

Abstract

A ferroelectric with a high phase‐transition temperature (Tc) is an indispensable condition for practical applications. Over the past decades, both strain engineering and the isotope effect have been found to effectively improve the Tc within ferroelectric material systems. However, the former strategy seems to prefer working in inorganic ferroelectric thin films, while the latter is also limited to some certain systems, such as hydrogen‐bonded ferroelectrics. It is noted that a mono‐fluorinated molecule is geometrically very similar to its parent molecule and the substitution of H by an F atom can introduce a chiral center on the molecule to template or stabilize polar structures. Significantly, the barrier of rotation of the fluorinated organic molecules is raised, resulting in a remarkable increase in Tc. Herein, by applying the molecular design strategy of H/F substitution to the organic–inorganic perovskite ferroelectric (pyrrolidinium)CdCl3 with a low Tc of 240 K, two high‐Tc chiral perovskite ferroelectrics, (R)‐ and (S)‐3‐F‐(pyrrolidinium)CdCl3 are successfully synthesized, for which the Tc reaches 303 K. The significant enhancement of 63 K in Tc extends the ferroelectric working temperature range to room temperature. This finding provides a new effective way to regulate the Tc in ferroelectrics and to design high‐Tc molecular ferroelectrics.

Defect Engineering on Electrode Materials for Rechargeable Batteries

“…Zhang and co‐workers directly used the inherent structural defects of nanocarbons to produce atomically dispersed Co–N x –C active sites through defect engineering. The obtained catalyst presented a layered porous structure with Co–N x –C group, nitrogen doping, oxygen functional group and topological defects, and high‐density active sites, making both ORR and OER have significant dual‐functional electrocatalytic activity under alkaline conditions . In addition, many studies indicated that the coordination between heteroatoms and metal in carbon materials, especially FeCo–N x –C, can significantly alter the electronic structure, so as to optimize the intermediate adsorption, thus showing better activity than noble metal catalysts .…”

A Freestanding Flexible Single‐Atom Cobalt‐Based Multifunctional Interlayer toward Reversible and Durable Lithium‐Sulfur Batteries

“…The XPS peak of CN in the NC@SA‐Co evidently shifts to a higher binding energy compared with that in NC. The result could be attributed to the binding of Co with N in the moieties of CoN x C, which is consistent with the results reported by other works . The element valence state of the single Co atom in the NC@SA‐Co was also investigated in detail using the XPS.…”

Uniform Lithium Nucleation Guided by Atomically Dispersed Lithiophilic CoNx Sites for Safe Lithium Metal Batteries

“…N 1s spectrum for CoNC reveals the coexistence of pyridinic (398.4 eV), pyrrolic (400.5 eV), graphitic (401.4 eV), oxidized (403.0 eV), and chemisorbed (405.2 eV) nitrogen species (Figure d). Compared with NGM (Figure S3f, Supporting Information), a new peak at 399.3 eV can be assigned to the N coordinated with Co, manifesting the presence of CoN x species . These results strongly indicate a high dispersion of single Co atoms in the porous CoNC layers with CoN x C configurations, which can potentially realize uniform deposition of Li metal.…”