Heterogeneous Ni-MOF/V₂CT_x-MXene hierarchically-porous nanorods for robust and high energy density hybrid supercapacitors

Interfacial engineering is an appealing strategy to construct heterogeneous nanostructures and tunes the morphology of metal-organic frameworks (MOFs) and MXenes for hybrid supercapacitors. Herein, a temperature-controlled annealing process is introduced to fabricate Ni-MOFs/V₂CT_x-MXene (T_x denotes the surface groups, -O, -OH, and -F) composites on Ni foam (NF) (namely MOF/MXene/NF) and subsequently build the heterogeneous structure of a hierarchically-porous nanorod composite without a change in the crystalline structure. Experimental characterizations and theoretical calculations reveal that Ni-O-V bridging bonds are constructed at the Ni-MOF and V₂CT_x interfaces, which could be used to establish a favorable electronic structure in promoting conductivity and reactivity. The optimized MOF/MXene/NF electrode obtained at 300 °C (i.e., MOF/MXene/NF-300) delivers an ultrahigh specific capacity of 1103.9 C g⁻¹ at 1 A g⁻¹. The as-assembled hybrid supercapacitor, composed of MOF/MXene/NF-300 as the cathode and activated carbon/NF as the anode, delivers a high energy density of 46.3 W h kg⁻¹ at a power density of 746.8 W kg⁻¹ and an outstanding cycling stability of ca. 118.1% capacity retention after 15 000 cycles. Such an achievement stems from the strong chemical bonds at the interface and unique porous morphology. This work suggests a new avenue for designing and preparing robust and high-performance electrode materials for hybrid supercapacitors.