Synergistic effects in 3D honeycomb-like hematite nanoflakes/branched polypyrrole nanoleaves heterostructures as high-performance negative electrodes for asymmetric supercapacitors

Rational assembly of unique branched heterostructures is one of the facile techniques to improve the electrochemical figure of merit of materials. By taking advantages of hydrogen bubbles dynamic template, hydrothermal method and electrochemical polymerization, branched polypyrrole (PPy) nanoleaves decorated honeycomb-like hematite nanoflakes (core-branch Fe₂O₃@PPy) are fabricated. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and scanning transmission electron microscopy in high angle annular dark field mode with electron energy loss spectroscopy were combined to elucidate the mechanisms underlying formation and morphogenesis evolution of core-branch Fe₂O₃@PPy heterostructures. Benefiting from the stability of honeycomb-like hematite nanoflakes and the high conductivity of PPy nanoleaves, the resultant core-branch Fe₂O₃@PPy exhibits an ultrahigh capacitance of 1167.8 F g⁻¹ at 1 A g⁻¹ in 0.5 M Na₂SO₄ aqueous solution. Moreover, the assembled bi-metal oxides asymmetric supercapacitor (Fe₂O₃@PPy//MnO₂) gives rise to a maximum energy density of 42.4 W h kg⁻¹ and a maximum power density of 19.14 kW kg⁻¹ with an excellent cycling performance of 97.1% retention after 3000 cycles at 3 A g⁻¹. These performance features are superior than previous reported iron oxide/hydroxides based supercapacitors, offering an important guideline for future design of advanced next-generation supercapacitors.