Nanoarchitectonics of self-grown copper selenide on copper for solid-state asymmetric supercapacitor

The ability of anode materials to store energy depends on their rate capability, which is limited by the slow reaction kinetics at the interface between the electrode and the electrolyte. Here, a self-supported Cu3Se2@Cu electrode was developed using a facile self-growth technique at various immersion times in sodium selenosulfate solution. The transformation of Cu to Cu(OH)2 and further into Cu3Se2 with alteration of surface morphology depends critically on the immersion time. A film with a nanosheet-type morphology prepared with 2 h immersion time achieved a specific capacitance of 928 F cm-2 at a scan rate of 2 mV s-1. Due to the open cage-like structure and nanosheet-type morphology, the self-grown electrodes had excellent electrochemical stability of 87 % over 5000 charge-discharge cycles. Having excellent high electrochemical activity, self-grown Cu3Se2 is ideal for the fabrication of supercapacitor devices and combined with activated carbon to assemble an asymmetric super -capacitor (ASC). The ASC provides an energy density of 30.8 Wh kg-1 at 461 W kg-1 with a retention of 98 % capacitance up to 5000 galvanostatic charge-discharge cycles. This study offers insight into the conversion of Cu substrate to Cu3Se2 for supercapacitor applications possessing high rate capacity and is expected to facilitate the development of self-grown selenide-based electrodes from the metal substrate providing new insights.