A Hierarchical Interconnected Nanosheet Structure of Porous δ-MnO₂ on Graphite Paper as Cathode with a Broad Potential Window for NaNO₃ Aqueous Electrolyte Supercapacitors

Abstract

The potential window for aqueous supercapacitor cathodes greatly depends on the electrochemical stability of water, and thus is generally limited to ∼1.2 V. Herein, a 1.4 V potential window (vs Ag/AgCl) in the 5 M NaNO 3 aqueous electrolyte for porous δ-MnO 2 with a hierarchical interconnected nanosheet structure grown on electrochemically roughened graphite paper by electrodeposition is reported. A specific capacitance of ∼407.6 F g −1 is delivered at 1 A g −1 , and capacitance retention up to ∼90.7% is achieved after 5000 cycles at 8 A g −1 . The aqueous asymmetric supercapacitors of 2.4 V are assembled with the configuration of δ-MnO 2 //activated carbon, and an energy density (E) of ∼38.4 Wh kg −1 is obtained at 599.7 W kg −1 (even at 12 kW kg −1 , E of ∼21.7 Wh kg −1 is still delivered). Moreover, the asymmetric supercapacitors exhibit good rate and cycling performance. Thanks to the simple preparation for the electrode materials/structures and high device performance, it is believed that this work provides valuable contributions to developing aqueous supercapacitors delivering a broad working voltage window and thus an elevated energy density.

Review on Current Progress of MnO2‐Based Ternary Nanocomposites for Supercapacitor Applications

“… The ion‐diffusion kinetics from the surface to the bulk of the MnO 2 electrodes is strongly affected by the ionic radius of the electrolytes [98,100,102] . Thus, α‐, γ‐, and δ‐MnO 2 display more stable electrochemical cycles in equimolar Li 2 SO 4 than that in Mg(NO 3 ) 2 electrolytes.…”

Aqueous Supercapacitor with Ultrahigh Voltage Window Beyond 2.0 Volt

“…The similar morphology MnO 2 ‐based aqueous SCs were further investigated by other researchers. Wang et al [ 26 ] and Dai and co‐workers [ 28 ] both fabricated porous MnO 2 ‐based electrodes by the facile electrochemical deposition method (Figure 3b). The corresponding ASCs achieved the voltage window of 2.2 and 2.4 V with improved capacity retention of 88.6% and 88.7% after 5000 cycles, respectively (Figure 3c–e).…”

“…b–e) Reproduced with permission. [ 26 ] Copyright 2020, American Chemical Society. f) Schematic of SSC structure and CV test of planar BDD electrode and porous BBD electrode.…”

Cracked bark-inspired ternary metallic sulfide (NiCoMnS4) nanostructure on carbon cloth for high-performance aqueous asymmetric supercapacitors

“…Among the various types of supercapacitors available commercially, those based on aqueous electrolytes are of particular interest because of their high safety, low cost, and good environmental friendliness [16][17][18][19][20]. However, given the low electrochemical stability of water, improvements in energy density, which are vital for the practical applications of aqueous supercapacitors, are difficult to implement by simply increasing the working voltage.…”