Regulating high specific capacitance NCS/α-MnO2 cathode and a wide potential window α-Fe2O3/rGO anode for the construction of 2.7 V for high performance aqueous asymmetric supercapacitors

Abstract

The long-term durability, safety, and high specific power, supercapacitors (SCs) hold unlimited promise for replacing non-renewable energy sources. Aqueous asymmetric supercapacitors (AASCs) offer numerous economic and environmental benefits. The small voltage of AASCs, however, limits their progress for large-scale industrial applications. AASCs with voltage windows (>2.0 V) have made significant progress in the last few years. Herein, a novel hierarchical α-Fe2O3 ultra-thin nanowires grown on rGO aerogel (denoted as α-Fe2O3/rGO) composite was designed as the anode. Taking advantage of the rGO aerogel protective layer, the α-Fe2O3/rGO anode reveals a prolonged voltage window up to -1.5–0 V, which considerably boosts capacitance up to (270 F g−1@1 A g−1), and (106.7 F g−1@ 10 A g−1) along with superb stability owing to the good integration of rGO network and α-Fe2O3. Moreover, NiCo2S4 nanosheets coated on α-MnO2 nanorods (denoted as NCS/α-MnO2) as a protection layer to complement the wide potential cathode, as a result, the NCS/α-MnO2 composite displays an optimized voltage window of 0–1.2 V, a high capacitance (594 F g−1@1 A g−1), and outstanding cycling stability. More importantly, the assembled NCS/α-MnO2//α-Fe2O3/rGO AASC device functions in an optimized voltage (2.7 V) by means of ultra-high specific energy of 142.1 Wh kg−1, at the specific power of 1350 W kg−1 with the downfall of the specific energy of 18.75 Wh kg−1 at the specific power of 67,500 W kg−1 with exceptional stability (79% of its initial capacitance retention). Additionally, we demonstrated a single AASC device with enough energy to light a 20 mW green LED and emitted light over 40 s, which opens up possible realistic applications. Finally, this study provides an avenue for fabricating and designing a wide voltage using a compositing technique, which seems to be one of the promising route to increase specific energy of AASCs.