Collaborative Research: Understanding the Materials Chemistry to Engage Anion Uptake and Release in Layered Transition Metal Oxides and Hydroxides

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Non-Technical SummaryLayered transition metal oxide and hydroxide materials capable of hosting anions could have many energy- and environment-related applications. However, most metal oxides and hydroxides cannot reversibly uptake and release anions, limiting their sustainable applications in various devices. In this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, the research team aims to understand how chloride and sulfate anions move in the layered materials and develop a library of layered transition metal oxide and hydroxide materials for reversible anion uptake and release. Atomic-scale modeling and quantum theory are used to build a property database of layered oxides, and gain fundamental insights into atomic interactions between anion and layered materials. The close integration of theory and experiment helps determine the underlying mechanisms of the anion insertion and extraction in the interlayer region of the host materials and to establish the fundamental roles of material local structures, anion, and water molecules for reversible hosting of chloride and sulfate into layered metal hydroxides. This project enhances education and outreach efforts by the research team to increase scientific engagement and participation from underrepresented groups through a range of activities aimed at the general public, high school students and teachers, undergraduate students, and graduate students.Technical SummaryLayered double hydroxides (LDHs) have two-dimensional positively charged nanosheets and host negatively charged ions and structural water molecules in the interlayer regions, offering advantages in a wide range of energy- and environment-related applications, including multivalent anion batteries, high-capacity desalination, and ion remediation. However, there is a lack of fundamental understanding of how the local structure and their atomic interaction with anions affect the reversible anion uptake and release in LDHs. In this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, the research team aims to understand the interplay between ion-hydration, atomic transport, material defect, and charge transfer on anion insertion and extraction in transition metal oxide and hydroxide layered materials. The team proposes to synthesize Fe- and Co-based LDH, [M2+1-x(M/Ni)3+x(HO−)2]x+ [(An−)n/2 · yH2O]x- (M: Fe, Co; A: inserted anion groups such as Cl- and SO42-,), where Ni3+-doping immobilizes the structural water in the interlayers and stabilizes the interlayer structure. The team plans to optimize LDH local structures (e.g., disorder and site defect) and long-range structure (e.g., interlayer distance, crystalline phase), guided by atomic modeling, to assist the anion uptake and release. The team plans to use neutron/X-ray total scattering and pair distribution function analysis and X-ray absorption spectroscopy to study how metal-oxygen (M-O) octahedra of LDHs interact with anions, water, and cation. The density functional theory calculations, advanced sampling, and molecular dynamics simulations are used to gain atomic-scale insights into interactions between M-O octahedra in the proposed LDHs, anions, and water, providing guidelines for experimentally tuning the interfacial structuring of the LDHs. The interwoven nature between the experimental and modeling efforts provides better-resolved structural details via experiments and simulations informing each other. The education and outreach efforts advance the team's goals to increase participation of students from underrepresented groups via an undergraduate researcher exchange program, hands-on activities for high school students and teachers, and advanced research training experiences for undergraduate and graduate students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.