δ-MnO2 (birnessite) is a layered transition metal oxide of interest for electrochemical energy storage. The interlayer of birnessite contains alkaline or alkaline earth metal cations and flexible water bound by electrostatic interactions to the manganese oxide layers. In aqueous electrolytes, we hypothesize that the interlayer water improves the energy storage kinetics. However, these water molecules can be removed under low pressure or raised temperature, both environments often experienced during electrode preparation. Because of the variability of material processing before electrochemical testing, we must investigate the stability of the interlayer water and its role in the energy storage kinetics of birnessite. To do this, we synthesized KxMnO2●yH2O (K-birnessite) via a hydrothermal method. We confirmed the synthesized material to be K-birnessite via Raman spectroscopy and X-ray diffraction (XRD ). The presence of interlayer water after heat treatment was investigated using thermogravimetric analysis and in situ XRD. To study a dehydrated form of the material, non-aqueous electrochemistry was performed in an argon environment. The interlayer was monitored throughout electrode processing using ex situ XRD. The material’s electrochemical energy storage capability in aqueous and non-aqueous electrolytes was investigated using cyclic voltammetry. This study sheds light on the sensitivity of interlayer water in birnessite during common energy storage electrode processing steps, and how it affects its electrochemical energy storage performance.

Investigating the role of interlayer water in δ-MnO2 during electrochemical energy storage

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.