Phosphate ions functionalized spinel iron cobaltite derived from metal organic framework gel for high-performance asymmetric supercapacitors.

Spinel iron cobaltite (FeCoO) with high theoretical capacity is a promising positive electrode material for building high-performance supercapacitors. However, its inherent poor conductivity and deficient electrochemical active sites hinder the improvement of its electrochemical kinetics behavior. Herein, phosphate ions modified FeCoO is obtained in the presence of oxygen vacancies (P-FeCoO) by a simple metal organic framework gel-derived strategy. Phosphate ions added on the surface of P-FeCoO greatly enhances its surface activity, thus prompting the faster charge storage kinetics of the electrode material. Due to its ample electrochemical active sites and rapid ion diffusion and electron mobility, the optimized P-FeCoO electrode delivers a superior specific capacity of 1568.8 F g (784.4 C g) at a current density of 1 A/g and has an excellent cycling stability with 93.3 % initial capacity retention ratio after 5000 cycles. More impressively, the assembled asymmetric supercapacitor consisting of P-FeCoO and activated carbon which act as positive and negative electrode materials, respectively displays a favorable energy density of 60.2 Wh kg at a power density of 800 W kg and has a long cycling lifespan. These results demonstrate the potential importance of modifying the surface of spinel cobaltite with phosphate ions and incorporating oxygen defects in it as a facile strategy for enhancing the electrochemical kinetics of electrode materials.