Self-Discharge Processes in Symmetrical Supercapacitors with Activated Carbon Electrodes

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Electric double-layer capacitors (EDLCs) are crucial for energy storage.
• Understanding self-discharge mechanisms in EDLCs is vital for performance optimization.
• Composite activated carbon electrodes and aqueous electrolytes present unique electrochemical behaviors.

Purpose of the Study:

• To investigate the self-discharge characteristics of EDLCs using composite activated carbon electrodes and aqueous magnesium sulfate electrolyte.
• To identify the key factors and phases governing the self-discharge process.
• To determine the optimal conditions for minimizing self-discharge.

Main Methods:

• Potentiostatic charge (stabilization) experiments were conducted on EDLCs.
• Discharge capacity was measured over time to quantify self-discharge.
• Electrode surface analysis was performed to understand material changes.

Main Results:

• Self-discharge was observed to increase significantly at voltages above 0.8 V.
• The self-discharge process was characterized by two distinct phases: initial charge redistribution and main charge transfer.
• Optimal stabilization conditions were identified as 50 minutes at 1.4 V.
• Long-term polarization led to hydrophilicity of the negative electrode due to epoxy functional group formation.

Conclusions:

• The self-discharge of aqueous EDLCs is voltage-dependent and involves distinct charge transfer mechanisms.
• Specific stabilization protocols can mitigate self-discharge losses.
• Electrode surface modifications, such as hydrophilicity, can influence EDLC performance during operation.