Metal–organic framework-derived high conductivity Fe3C with porous carbon on graphene as advanced anode materials for aqueous battery-supercapacitor hybrid devices

Battery-supercapacitor hybrid (BSH) devices with aqueous electrolytes receive extensive attention due to their high potential. In this study, porous carbon coated Fe3C nanoparticles (C/Fe3C) are loaded onto reduced graphene oxide (rGO) nanosheets, forming rGO@C/Fe3C composite structure. The rGO@C/Fe3C composite is prepared by in-situ carbonization of rGO/Fe-MOFs. First-principles calculation proves that the high conductivity of the Fe3C mainly comes from d electrons of Fe and therefore can benefit the rate capability. The optimized electrode structure of rGO@C/Fe3C displays high capacity of 95.3 mAh g−1 at 1 A g−1, enhanced rate performance (retaining 66.5% at 20 A g−1) and outstanding cycling stability (retaining 81.5% after 5000 cycles). Furthermore, a BSH device with Na0.5MnO2 cathode and rGO@C/Fe3C anode structure shows an ultrahigh output voltage of 2.4 V in 1 M Na2SO4 electrolyte, while its output voltage in 6 M KOH electrolyte is only 1.4 V. The observed energy densities of the device in two electrolytes are 46.2 Wh kg−1 at 1.2 kW kg−1 and 28.3 Wh kg−1 at 0.7 kW kg−1, respectively. Therefore, the successful construction of the BSH device based on Fe3C/rGO provides an attractive strategy for the selection of anode materials. [Display omitted] •The rGO@C/Fe3C is synthesized by in situ carbonization of the rGO/Fe-MOFs.•The rGO@C/Fe3C electrode show the specific capacity of 95.3 mAh g−1 at 1 A g−1.•A battery-supercapacitor hybrid device is assembled as Na0.5MnO2//rGO@C/Fe3C.•The Na0.5MnO2//rGO@C/Fe3C device shows an ultrahigh output voltage of 2.4 V.