Electrochemical Performance of Delafossite, AgFeO <sub>2</sub> : A Pseudo-Capacitive Electrode in Neutral Aqueous Na <sub>2</sub> SO <sub>4</sub> Electrolyte
Abhay Narayan Singh, Rakesh Mondal, Chandana Rath, Preetam Singh
Abstract
Layered delafossite AgFeO 2 with open channel structure is envisaged as a pseudo capacitor electrode using Fe 2+ /Fe 3+ redox couple. A simple co-precipitation method was employed for the phase formation of delafossite AgFeO 2 resulting in a mixture of 2H and 3R-phase. Phase tuning of 2H phase was done by controlling the calcination conditions and characterizing by powder XRD, FT-IR, and Raman methods. 2H AgFeO 2 was used to synthesize as a majority phase because it have the larger inter layer spacing than 3R phase shown. HRTEM study confirms the formation 2H phase in majority. All of the synthesized samples exhibit predominantly faradic battery-type redox behavior along with surface charge storage. Flower like microarchitectures of AgFeO 2 show outstanding electrochemical performance with high specific capacity of 110.4 F g −1 at 1 A g −1 current density, that retained up to 89% after 2000th times charge/discharge in 1 M Na 2 SO 4 electrolyte. In an asymmetric device mode, AFO-400//AC full cell exhibits superior electrochemical performance by delivering high energy density (33.5 Wh kg −1 ) and high power density (454.3 W kg −1 ) with excellent cycling stability (86% retention after 2000th cycles). The results clearly demonstrate that the synthesized delafossite AgFeO 2 containing mixture of 2H and 3R-phases have remarkable potential to be used as a negative electrode material for supercapacitor and other energy storage technologies.