Hierarchical web-like NiFeMn ternary hydroxides microstructure assembled on reduced graphene oxide for binder-free supercapacitor electrode

In this work, a novel hierarchical web-like microstructure was fabricated by aligning interconnected NiFeMn hydroxide garlands on rGO-modified Ni foam (NiFeMn hydroxide/rGO/Ni foam) with a one-pot two-step hydrothermal method. During the first step at 50 °C, the redox reaction between GO and Ni foam results in the formation of rGO membrane on Ni foam. During the second step at 135 °C, urea decomposed and the produced NH3·H2O reacted with metal cations to form amorphous NiFeMn ternary hydroxide. The obtained binder-free electrode was characterized with scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectroscopy (XRD), Raman spectroscopy and Brunauer-Emmett-Teller gas sorptometry measurements (BET). The electrochemical performances of NiFeMn hydroxide/rGO/Ni foam were investigated with cyclic voltammetry (CV) and galvanostastic charge/discharge technique (GCD). NiFeMn hydroxide/rGO/Ni foam presents a high areal capacity of 35.1 C cm−2, capacity retention of 81.1% after 5000 GCD cycles at 30 mA cm−2 and excellent rate capability. The asymmetric supercapacitor (ASC) assembled with NiFeMn hydroxide/rGO/Ni foam and activated carbon (AC) presents a ultra-high energy density of 40.73 W h m−2 at the power density of 79.38 W m−2, suggesting its good application prospect in energy storage.