Boosting enhanced capacitive deionization of H₂TiO₃/carbon electrodes by yolk-shell construction

Area of Science:

• Materials Science
• Electrochemistry
• Environmental Science

Background:

• Capacitive deionization (CDI) is crucial for sustainable water desalination.
• Layered metatitanic acid (HTO) shows potential for ion separation but suffers from low conductivity.
• Coupling HTO with carbon improves charge transfer and CDI performance.

Purpose of the Study:

• To develop and evaluate a yolk-shell structured HTO/carbon electrode (ys-HTO@C) for enhanced CDI performance.
• To investigate the desalination and ion-selective separation capabilities of the novel electrode.
• To understand the mechanisms behind electrode performance and degradation.

Main Methods:

• Fabrication of yolk-shell (ys-HTO@C), core-shell (cs-HTO@C), and bulk HTO electrodes using a stepwise nanoscale architectonic strategy.
• Electrochemical characterization including desalination tests (Na+ adsorption capacity, charge efficiency, cycling stability).
• Ion selectivity analysis for Li+, Na+, Ca2+, Mg2+, and Pb2+ extraction from synthetic and natural brines.

Main Results:

• The ys-HTO@C electrode demonstrated a Na+ adsorption capacity of 53.1 mg g-1 and a charge efficiency of 0.68.
• Electrode performance was superior to core-shell and bulk counterparts due to enhanced charge transfer and storage.
• The electrode exhibited preferential Li+ capture over other ions, with a Li+/Na+ separation factor up to 60.7 in natural brine.
• Capacity fading was attributed to carbon oxidation and HTO degradation during cycling.

Conclusions:

• The yolk-shell construction strategy effectively enhances HTO/carbon electrode performance for CDI.
• The developed electrode shows significant potential for efficient water desalination and selective lithium extraction from complex brines.
• Further research into mitigating degradation mechanisms is recommended for improved long-term stability.