Three-dimensional nanoporous N-doped graphene/iron oxides as anode materials for high-density energy storage in asymmetric supercapacitors

There is considerable interest in developing novel electrode materials for storing/delivering more energy than carbonaceous materials at fast charge/discharge rates. Here we demonstrate nitrogen-doped graphene/iron oxide hybrid electrode with three-dimensional nanoporous architecture (NP NDG/FeOx) as one of promising anode materials in asymmetric supercapacitors. Such NP NDG/FeOx hybrid electrode simultaneously has low internal resistance (5.4 ohms) and high specific capacitance (∼409 mAh g−1) because of its unique architecture, in which the constituent FeOx serves as electroactive material to improve the charge-storage density while the in-situ grown NDG facilitating the electron transport. This enlists the nickel-iron battery-like asymmetric supercapacitors (ASC), which are assembled with NP NDG/FeOx and Ni/Ni(OH)2 hybrid electrodes as anode and cathode, to exhibit durable pseudocapacitive energy storage in a wide voltage window of 1.7 V in aqueous electrolyte. The energy storage with maximum energy density of ∼142 Wh kg−1 is close to the values in lithium-ion batteries and much higher than that of lead-acid battery or Ni-MH battery, at the power delivery of 1.4 kW kg−1. The impressive performance makes it promising candidate as an anode material in next-generation ASC devices.