Controlled N-doped Fe3O4@C arrays: Achieving enhanced donor density and capacity for hybrid supercapacitors

Nitrogen-doped Fe2O3 (N–Fe2O3) nanorod array was directly grown on a carbon cloth and further modified via carbon coating (N–Fe3O4@C), exhibiting better structural stability. [Display omitted] •The optimal N-doping temperature was explored for achieving the high specific capacitance of N–Fe2O3.•The donor density of N–Fe2O3 was quantitatively analyzed.•Nitrogen-doping and carbon shell effectively decrease the potential barrier of ion migration of the oxides.•N–Fe3O4@C showed greatly enhanced conductivity, capacity, and stability. Carbon modified nitrogen-doped Fe3O4(N–Fe3O4@C) nanorod array directly grown on carbon cloth was fabricated. Nitrogen-doping and carbon shell effectively decrease the potential barrier of ion migration of the oxides and improve the electrochemical performance. An enhanced donor density of N-Fe2O3 (7.6 × 1015 cm−3) is achieved with optimized doping temperature. Following with carbon coated, the optimized N–Fe3O4@C electrode showed ultrahigh capacitance over an extended potential window and remarkable cycling performance. A new quasi-solid-state supercapacitor with N–Fe3O4@C and NiCoP@Ni(OH)2 achieved high voltage to 2.0 V and high energy density (72.37 Wh kg−1, 2.36 mWh cm−3).