Zwitter Ion-Promoted Hybrid 2D Materials for Energy Applications
Authors: Ghimire Suvash , Aceta Yara , Pour Gavin , Crawford Kaitlyn E , Mukhopadhyay Kausik 
Published: November 2022

Layer-by-layer assembly of thin films have received growing interest in a variety of applications worldwide. Methods for depositing films, patterning, unconventional assemblies, and approaches are gaining immense scientific advancements. The porous structures, tunable surface areas, remarkable thermal and mechanical stabilities, abundant reserves, and cost-effectiveness makes clays one of the most sought-after materials for plethora of applications. Interestingly, several naturally occurring silicates, viz. clay minerals have layered structure with possibility of interchangeable intercalated ions and tunable chemical properties. Among these clay minerals, Bentonite is very promising owing to its abundance, low cost, high surface area, porosity, and unique layered structure. Clay is composed of alternating tetrahedral silica (T) and octahedral alumina (O) sheets arranged in 1:1 ratio (T-O). The tetrahedral sheets are formed from Si4+ ions coordinated with oxygen, however in the octahedral sheet Al3+ metal ion is the central atom. Notably, naturally occurring Bentonite have some of the octahedral sites occupied by the Mg2+ and Fe2+ ions. The presence of these ions shows the tunable property of the octahedral layer that can concomitantly widen its applicability in the energy fields. Herein, we have put a focused effort in developing a sustainable, cost-effective, environmental benign, and biocompatible clay films having unique physical and chemical properties. We present a unique approach to develop clay galleries infused with intercalating quaternary ammonium salts. The insertion of such zwitter ions enhances the interlayer spacing, while simultaneously allowing to form durable clay films. The hybrid clay films have been characterized using the powder X-ray diffraction, X-ray photoelectron spectra, ATR-FTIR spectra, DSC-TGA, dynamic mechanical analyses, and imaging techniques. Effect of varying the carbon chain length in these zwitter ions have been verified to have a significant impact in controlling the interlayer spacing in the clay films. Further, the intercalation using zwitter ions led to the alternations in the electron environment of the dielectric silicate layers that has been confirmed using electrochemical and impedance spectroscopy studies. Owing to the high electronic resistance and high ionic conductivity present in the films, a series of impedance spectroscopy experiments were conducted in variety of electrolytes. The ionic conductivity of the hybrid clay films is remarkable, and a correlation have been established with the ionic size of the conducting ions. In metal ion batteries, where dendritic growth causes thermal degradation of the batteries, the hybrid clay films possess high thermal and mechanical stability that makes them versatile for energy materials. can provide The abundance and sustainability of clay minerals and a cost-effective approach to engineer these hybrid films may provide efficient avenues to develop new generation of battery separators and capacitors for future.