Oxide Acidity Modulates Structural Transformations in Hydrogen Titanates during Electrochemical Li-Ion Insertion.

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Hydrogen titanates (HTOs) are metastable, layered titanium oxides with interlayer water and protons.
• Understanding the role of interlayer chemistry is crucial for HTOs' electrochemical applications, particularly Li+ insertion.

Purpose of the Study:

• To investigate how the interlayer chemistry of HTOs influences electrochemical Li+ insertion.
• To correlate electrochemical performance with physical and chemical properties of HTOs.

Main Methods:

• Operando X-ray diffraction
• In situ differential electrochemical mass spectroscopy
• Solid-state proton nuclear magnetic resonance
• Quasi-elastic neutron scattering
• First-principles density functional theory (DFT) calculations

Main Results:

• The potential for the first reduction reaction correlated with the acidity of structural protons.
• Electrochemical reduction of structural protons produces hydrogen gas (H2) and lithiated HTOs.
• Generated H2 gas is confined within the HTO lattice until subsequent oxidation.

Conclusions:

• Electrochemical electron transfer to structural protons is a key mechanism in HTOs.
• Hydrogen evolution can occur below the standard hydrogen reduction potential in HTOs.
• Findings have implications for designing insertion hosts containing hydrogen and water for electrochemical energy storage.