Functionalized 2D Silicate-Based Films for Energy Applications

Clay is one of the oldest known silicate-based materials to humans and has been an integral part to our civilization from the prehistoric era, that includes pottery, tiles, art objects, bricks, tools, medicinal properties, ceramics and ancient batteries (Baghdad batteries). The layered structures of clay with interchangeable ions can be tuned for various applications that include energy storage, sensing, wastewater treatment, polymer composites, fire-resistant materials, cosmetics, and biomedical materials. Additionally, its abundant supply, low cost, high porosity, high surface area, and good thermal barrier and mechanical properties make clay a highly deserving material for high-valued applications. Among various energy storage and conversion materials, functionalized natural clays display significant potentials as electrodes, electrolytes, separators, and nanofillers in energy storage and conversion devices. In addition, natural clays deliver the advantages of high ionic conductivity and hydrophilicity, which are beneficial properties for solid-state electrolytes. Herein, we show a unique approach to engineer hybrid clay films using simple precursors viz. earth-abundant clay, water, and a quaternary ammonium salt. The quaternary ammonium salt arranges in monolayer, bilayer, and pseudo-tri-layer structure into the clay gallery, allowing to tune the basal spacing of the material. In the present study, we have varied the carbon chain length of the quaternary ammonium salt from lower to higher carbon chain length. The low-carbon chain quaternary ammonium salts arranged themselves in a pseudo-tri-layer configuration, increasing the basal spacing to a higher value compared to high-carbon chain modifications. The above parameters have been well characterized using powder X-ray diffraction and infrared spectroscopy studies. In addition, the engineered clay films have also been characterized using x-ray photoelectron spectroscopy, scanning electron microscopy, and x-ray fluorescence techniques to explore the films' structural and morphological parameters. Furthermore, we have analyzed for impedance spectra of the engineered clay films in non-aqueous electrolyte solutions. The spectra exhibit lower electrochemical series resistance (ESR) values for the non-metallic and monometallic clay films against the parent clay material. Moreover, a bimetallic analogue of the clay films showed a further decrease in the ESR values, which show glimpses of new ventures into non-lithiated and non-sulfur based materials used in energy application, esp. batteries, electrodes. Additionally, using the right chemical modifications, newly developed hybrid clay films can be engineered as cost-effective battery separators and capacitors. The unique methodology could address the challenges posed by energy industries, agencies and researchers, and usher new pathways for developing a sustainable and biocompatible materials energy applications using a cost-effective approach.