Lattice Water Deprotonation Enables Potassium-Ion Chemistries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Electrochemical water splitting is crucial for clean energy, typically relying on catalytic material surfaces.
• Hydrated materials often serve as inactive frameworks, limiting their application in energy storage.

Purpose of the Study:

• To investigate anomalous water deprotonation within Fe-Mg oxalate hydrated lattices.
• To explore the potential of this phenomenon in designing novel cathode materials for potassium ion storage.

Main Methods:

• Density Functional Theory (DFT) calculations to model water splitting within the material lattice.
• Electrochemical experiments to validate predicted behavior and assess potassium ion storage performance.
• Isotopic tracing to confirm hydrogen evolution from crystal water.

Main Results:

• Observed anomalous partial water splitting (deprotonation) within the Fe_1-xMg_x(C₂O₄)•2H₂O lattice.
• Identified redox-active Fe sites responsible for splitting crystal water into hydroxyls and hydrogens during initial charging.
• Demonstrated that this process activates the framework for reversible potassium ion storage, with Mg sites stabilizing the structure.
• Experimental validation and isotopic tracing confirmed hydrogen evolution from crystal water.

Conclusions:

• The "water deprotonation in lattice" phenomenon activates otherwise inactive hydrated materials for electrochemical applications.
• This discovery offers a new strategy for designing advanced cathode materials through electrolysis-assisted electrochemistry.
• The Fe-Mg oxalate system serves as a model for this novel approach to energy storage material design.