Sustainable production of nano α-Fe2O3/N-doped biochar hybrid nanosheets for supercapacitors

Abstract

Transition metal oxide (TMO)/carbon hybrid materials have shown great potential in energy storage applications. However, their facile, environmentally friendly, cost-efficient and scalable production still remains a challenge. Herein, two-dimensional nano α-Fe₂O₃/N-doped biochar hybrid nanosheets (α-Fe₂O₃/NBCS) derived from biomass waste were successfully fabricated via a molten salt route. The molten salt would hinder the decomposition of the carbon framework so that the direct one-step fabrication of an iron oxide/biochar hybrid in an air atmosphere at high temperature could be achieved. The introduction of biomass waste could reduce the crystallite size of α-Fe₂O₃, and the O₂ in air could facilitate the formation of α-Fe₂O₃, while Fe₃O₄ was obtained in Ar due to the presence of reducing power of biomass carbon. Compared to the pure α-Fe₂O₃ sample, the hybrid material showed a much-improved electrochemical performance because of the synergistic effect of α-Fe₂O₃ and N-doped biochar nanosheets. When applied as the negative electrode material, it exhibited a high specific capacitance of 452.3 F g⁻¹ at 2 A g⁻¹ with a good rate capability in a three-electrode system, and a satisfactory energy density of 17.9 W h kg⁻¹ was obtained in an asymmetric supercapacitor with a fungal manganese oxide-based positive electrode. The satisfactory results suggested that the fabricated α-Fe₂O₃/NBCS could be a candidate of negative electrode materials for supercapacitor applications. Overall, this work provides an environmentally friendly and cost-efficient route to synthesize TMO/carbon hybrid materials with a simplified synthetic procedure for large-scale production accompanied by the high value-added conversion of biomass waste.