Synergistic Interface-Assisted Electrode-Electrolyte Coupling Toward Advanced Charge Storage.

Abstract

Owing to the limited charge storage capability of transitional metal oxides in aqueous electrolytes, the use of redox electrolytes (RE) represents a promising strategy to further increase the energy density of aqueous batteries or pseudocapacitors. The usual coupling of an electrode and an RE possesses weak electrode/RE interaction and weak adsorption of redox moieties on the electrode, resulting in a low capacity contribution and fast self-discharge. In this work, Fe(CN)₆ ^4- groups are grafted on the surface of Co₃ O₄ electrode via formation of CoN bonds, creating a synergistic interface between the electrode and the RE. With such an interface, the coupled Co₃ O₄ -RE system exhibits greatly enhanced charge storage from both Co₃ O₄ and RE, delivering a large reversible capacity of ≈1000 mC cm^-2 together with greatly reduced self-discharge. The significantly improved electrochemical activity of Co₃ O₄ can be attributed to the tuned work function via charge injection from Fe(CN)₆ ^4- , while the greatly enhanced adsorption of K₃ Fe(CN)₆ molecules is achieved by the interface induced dipole-dipole interaction on the liquid side. Furthermore, this enhanced electrode-electrolyte coupling is also applicable in the NiO-RE system, demonstrating that the synergistic interface design can be a general strategy to integrate electrode and electrolyte for high-performance energy storage devices.