Nature of the electric double layer to modulate the electrochemical behaviors of Fe2O3 electrode

The electric double layer (EDL) has been found to play a critical role in not only electric double-layer capacitors (EDLCs) but also batteries and electrocatalysts. Although the influence of EDLs on the electrochemical behaviors of electrolytes has been extensively investigated, its influence on the electrode itself, particularly the energy storage mechanism, remains unclear. Herein, using popular α-Fe2O3, we look into the interaction between electrode and EDL and find the energy storage mechanism of an electrode can be tuned by modulating EDL. The EDL, which is mainly influenced by the inner Helmholtz plane (IHP) through the specific adsorption of ions onto the surface of Fe2O3, determines which ions are present at the interface and how they react with the electrode. Ultimately, the composition and properties of the EDL determine the energy storage mechanism of an Fe2O3 electrode, including conversion reaction, ions insertion, surface redox reaction and pseudocapacitance. Our results not only provide a new understanding on the nature of the EDL but also demonstrate that the EDL should be promoted as a functional "component" which can be designed for achieving the optimum synergy of an electrode-electrolyte interface.