Aqueous Multivalent Charge Storage Mechanism in Aromatic Diamine-Based Organic Electrodes

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Aqueous rechargeable batteries offer enhanced safety and cost-effectiveness over organic electrolyte systems.
• Multivalent ion-based aqueous batteries are crucial for achieving high energy density.
• Organic electrodes are attractive for their tunability and potential for sustainable energy storage.

Purpose of the Study:

• To investigate the electrochemical behavior of poly(ortho-phenylenediamine) (PoPD) as an organic electrode material in aqueous electrolytes containing multivalent ions (Zn2+ and Al3+).
• To elucidate the ion transport and storage mechanisms within the PoPD electrode during battery cycling.
• To evaluate the performance of PoPD-based electrodes in terms of capacity, rate capability, and cycle life.

Main Methods:

• Synthesis of PoPD via electropolymerization.
• Electrochemical characterization including cyclic voltammetry and galvanostatic charge-discharge cycling.
• Structural and mechanistic investigations using electrochemical quartz crystal microbalance (EQCM), time-dependent Fourier transform infrared (FTIR) spectroscopy, electrochemical impedance spectroscopy (EIS), and ex situ X-ray diffraction (XRD).

Main Results:

• PoPD electrodes exhibit reversible insertion/extraction of both multivalent ions (Zn2+, Al3+) and protons.
• The electrodeposited PoPD electrode is intrinsically conductive, eliminating the need for carbon additives and binders.
• The electrode demonstrates excellent rate performance and prolonged cycle life, achieving capacities of ~110 mAh g-1 in AlCl3 and ~93 mAh g-1 in ZnSO4 after 1000 cycles at 5C.
• Discharge products remain stable in the aqueous electrolyte.

Conclusions:

• Poly(ortho-phenylenediamine) is a promising intrinsically conductive organic electrode material for high-performance aqueous rechargeable batteries.
• The dual mechanism involving multivalent ions and proton co-insertion contributes to the electrode's capacity and stability.
• The binder- and additive-free nature of the PoPD electrode simplifies battery assembly and enhances sustainability.