Achieving Insertion-Like Capacity at Ultrahigh Rate via Tunable Surface Pseudocapacitance

Abstract

The insertion/deinsertion mechanism enables plenty of charge-storage sites in the bulk phase to be accessible to intercalated ions, giving rise to at least one more order of magnitude higher energy density than the adsorption/desorption mechanism. However, the sluggish ion diffusion in the bulk phase leads to several orders of magnitude slower charge-transport kinetics. An ideal energy-storage device should possess high power density and large energy density simultaneously. Herein, surface-modified Fe₂O₃ quantum dots anchored on graphene nanosheets are developed and exhibit greatly enhanced pseudocapacitance via fast dual-ion-involved redox reactions with both large specific capacity and fast charge/discharge capability. By using an aqueous Na₂SO₃ electrolyte, the oxygen-vacancy-tuned Fe₂O₃ surface greatly enhances the absorption of SO₃²⁻ anions that majorly increase the surface pseudocapacitance. Significantly, the Fe₂O₃-based electrode delivers a high specific capacity of 749 C g⁻¹ at 5 mV s⁻¹ and retains 290 C g⁻¹ at an ultrahigh scan rate of 3.2 V s⁻¹. With a novel dual-electrolyte design, a 2 V Fe₂O₃/Na₂SO₃//MnO₂/Na₂SO₄ asymmetric supercapacitor is constructed, delivering a high energy density of 75 W h kg⁻¹ at a power density of 3125 W kg⁻¹.

Tunable chemical adsorption of redox anions is achieved by surface-modified Fe₂O₃ quantum dots anchored on graphene nanosheets, exhibiting greatly enhanced pseudocapacitance via fast dual-ion-involved redox reactions and fast charge/discharge capability. Significantly, the electrode achieves a high capacity up to 749 C g⁻¹ in the Na₂SO₃ electrolytes and retains 290 C g⁻¹ at an ultrahigh scan rate of 3.2 V s⁻¹.

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