A Quasi-Solid-State Asymmetric Supercapacitor Device Based on Honeycomb-like Nickel–Copper–Carbonate–Hydroxide as a Positive and Iron Oxide as a Negative Electrode with Superior Electrochemical Performances

Here, we have fabricated a high performance asymmetric supercapacitor (ASC) device consisting of honeycomb-like nickel–copper–carbonate–hydroxide (NC) coated stainless steel (SS) as a positive and iron oxide nanoparticle (Fe2O3 NPs) coated SS as a negative electrode, separated by a poly(vinyl alcohol)–potassium hydroxide (PVA–KOH)-based gel membrane. Both of the component electroactive materials were synthesized via substrate-free polyvinylpyrrolidone (PVP) assisted facile hydrothermal protocols. The as-synthesized NC with numerous interconnected nanoflakes and mesoporous Fe2O3 NPs exhibits superior electrochemical properties. As an outcome, NC and Fe2O3 display specific capacitance (Csp) values of ∼1706.2 and 221.5 F g–1 (at 1 A g–1 current density), respectively, accompanied by an improved retention of their inherent Csp (∼94.4% for NC and ∼95.7% for Fe2O3) after 3000 galvanostatic charge–discharge (GCD) cycles at 1 A g–1. Finally, our assembled ASC device reveals an energy density value of ∼40.03 Wh kg–1 with a power density of ∼325.4 W kg–1 at 1 A g–1. Noticeably, the ASC retains an energy density of ∼27.2 Wh kg–1 (with a power density of ∼3250 W kg–1) even at 10 A g–1. Moreover, the ASC retains ∼88.1% of its original Csp after 10 000 successive GCD cycles. Thus, the ASC device with adequate electrochemical performance is highly promising for portable and flexible electronics.