NiFe2O4 quantum dots anchored on flower-like Ni-MOF with enhanced electrochemical performance for supercapacitors

Abstract

In this study, we successfully synthesized a NiFe₂O₄ quantum dots (QDs)@Ni-based metal–organic framework (Ni-MOF) microflower composite material. By utilizing ultrathin nanosheets for layer-by-layer assembly, the flower-like MOF with an open hierarchical structure, large specific surface area, and ordered pores was formed. It provided suitable accommodation space for the quantum dots, effectively avoiding their aggregation. Moreover, transition metal oxide (TMO)-based QDs possess high conductivity and a rich range of valence states, which can compensate for the deficiencies in the conductivity and stability of MOFs. This QDs@MOF composite increases the number of exposed active sites in the electrode and reduces the diffusion path of electrolyte ions, resulting in more active redox reactions and enabling fast charge transfer. The NiFe₂O₄ QDs@Ni-MOF-10 electrode achieves a specific capacity of up to 852.3 mA h g⁻¹ at a current density of 1 A g⁻¹. The assembled hybrid supercapacitor (HSC) device exhibits an energy density of 32.5 W h kg⁻¹ at a power density of 798 W kg⁻¹ and a wonderful capacity retention of 87.3% at 1 A g⁻¹ after 5000 cycles. Therefore, these results indicate that the combination of QDs and MOFs has great potential for applications in the field of supercapacitors.