Intercalation chemistry and charge storage in solution-processed layered MOPO₄ (M = V, Nb) hydrates




Zhu, Yue, Ph. D.

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Intercalation chemistry, despite being an old field with more than a century of history, has recently gained renewed interest owing to the rise of two-dimensional (2D) nanomaterials and their associated scientific and technological importance. The relevance of intercalation chemistry to this family of materials includes liquid exfoliation of layered materials, tuning their physical and chemical properties by intercalation, charge storage in thin 2D nanosheets, electrochemical intercalation in 2D heterostructures, etc. Some are old topics demanding fresh understanding in new material systems, and some are unprecedented ideas that will be exciting to explore. This dissertation examines intercalation chemistry and charge storage in layered MOPO₄ (M=V, Nb) hydrates, which is an interesting material system that differs in several unique ways from many previously studied intercalation hosts. This system is also less popular in literature compared with classic ones, such as graphite and transition metal dichalcogenides, but is more structurally complicated and offers more research opportunities. Historically, some aspects of the intercalation product and kinetics regarding the use of a bulky metallocene as intercalation guest remain elusive, and the charge storage mechanism of small alkali-ions in the presence of interlayer water has not been well understood. This work presents research efforts to answer such open questions in these materials through a combined experimental and theoretical approach. Following a brief overview of intercalation chemistry and its most up to date development (Chapter 1), materials synthesis involving solution processing methods to obtain microcrystals and nanosheets of MOPO₄ hydrates is described (Chapter 2). The subsequent in-depth studies are divided into two major parts using either microcrystals or nanosheets as intercalation host. The first part discusses the intercalation of ferrocene into microcrystals of VOPO₄·2H₂O in terms of resolving intercalated structures and understanding solvent-dependent kinetics (Chapter 3). The second part details the charge storage in nanosheets of MOPO₄ with implications on Li- and Na-ion battery applications (Chapter 4). Finally, key contributions to the intercalation chemistry of the title material system are summarized and possible future directions are provided (Chapter 5).


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