A multicore-shell architecture with a phase-selective (α plus δ)MnO2 shell for an aqueous-KOH-based supercapacitor with high operating potential

State-of-the-art aqueous-KOH-based asymmetric supercapacitors (ASCs) that have been reported thus far suffer from a low operating potential and low energy density that is bottlenecked by a theoretical voltage limit for water decomposition (1.23 V). Therefore, optimizing low-cost active electrode materials in an appropriate architecture is essential for developing advanced and cost-effective ASCs that resolve the hindrances listed above. Herein, a multicore-shell hierarchical nanoarchitecture with an outer shell formed from phase-selective growth of monoclinic alpha-MnO2, containing 2D tunnels within the lattice, and birnessite delta-MnO2, containing infinite-2D sheets, and a carbon-coated zinc-nickel-cobalt-based ternary metal oxide as a core ((alpha + delta)MnO2@C@ZNCO) is successfully designed and characterized. An ASC with (alpha + delta)MnO2@C@ZNCO as a positive electrode and zeolitic imidazolate framework (ZIF-8) implanted B and N-doped electrospun carbon nanofibers (Z-BN-CNFs) as a negative electrode exhibits an ultrahigh energy density of 79.8 W h kg(-1) at a power density of 846.18 W kg(-1) along with a maximum power density of 42.48 kW kg(-1) at a high energy density of 53.1 W h kg(-1). Furthermore, a capacitance retention of 66.5% with a current density from 1 to 50 A g(-1) and an excellent cyclic stability of 95.2% capacitance retention after 10 000 continuous charge-discharge cycles are also observed. The present success of fabricating a 1.7 V aqueous-KOH-based ASC with ultrahigh energy density will pave the way for new research toward low-cost ASCs with a high operating potential and high energy density.