Controlled Synthesis Of NiCo₂O₄@MOF Hybrid Electrode Material And Their Energy-storage Properties In Supercapacitors

In recent years,a series of flexible electronic products such as wearable flexible devices,roll-up displays,electronic skins,and flexible sensors have developed rapidly,which has created the demand for flexible energy storage devices.Supercapacitors have received wide attention and expectation from researchers owing to its low maintenance costs,high energy density and power density,fast charge and discharge performance,long life and good safety.In this paper,we preserve the high specific surface area,the morphological structure controllable and abundant redox active sites of MOFs materials,and a series of studies have been carried out on poor conductivity of MOFs supercapacitor electrode material:(1)By using a simple hydrothermal method and annealing treatment,the NiCo2O4 array material were prepared with different topography such as nanowires,nanosheets and honeycomb nanosheets.The NiCo2O4 nanowires,nanosheets and honeycomb nanosheets electrode materials exhibit excellent electrochemical performance that when used as a supercapacitor electrode material,and can reach 54.5,39.0,and 41.7 mAh/g at a current density of 2 mA/cm2,respectively.Moreover,the NiCo2O4 nanowires,nanosheets and honeycomb nanosheets electrode materials showing good rate performance,when the current density reaches 20 mA/cm2,the capacity retention ratios are 82.3%,82.1%and 73.5%,respectively.The NiCo2O4 nanowires have the best electrochemical performance in the comparison of electrochemical properties of three topographic NiCo2O4 materials.(2)NiCo2O4@Ni-MOF core-shell arrays was successfully grow on carbon cloth by using NiCo2O4 nanowires as a skeleton with secondary solvothermal method.Meanwhile,the effect of reaction time and loading on the electrochemical properties of composites was systematically investigated.Benefit from its unique layered core-shell structure and the synergistic effect between NiCo2O4 and Ni-MOF materials,the NiCo2O4@Ni-MOF(12 h)exhibits high specific capacity(208.8 mAh/g at 2 mA/cm2).Furthermore,when the current density reaches 20 mA/cm2,the material exhibits excellent rate performance and its capacity remains alternative to 68.2%.In addition,NiCo2O4@Ni-MOF(12 h)composite has better conductivity than pure Ni-MOF.(3)The flexible solid supercapacitor is assembled based on NiCo2O4@Ni-MOF composite material,delivering a high energy density of 32.6 Wh/kg at 348.9 W/kg without sacrificing its excellent cycling stability(nearly 100%retention over 6000 cycles).Furthermore,the device can be operated stably at different bending angles.The assembled flexible solid supercapacitor successfully driven the work of the electronic watch.