Application Of NiMoO₄ Containing Oxygen Vacancies In Supercapacitors

The rapid development of the global economy has accelerated the consumption of fossil energy and has induced increasingly serious energy and environmental crises,which have had a great impact on the survival and development of mankind.People are not only actively seeking renewable energy,but also actively developing various new and reliable energy storage and conversion devices.Supercapacitors（SCs）are also known as electrochemical supercapacitors.Compared with similar products（such as batteries,fuel cells and traditional capacitors）,they have higher power density and longer life expectancy,which has attracted extensive research attention.And is considered to be an essential energy storage device.It is worth noting that due to its unique advantages,including simple and safe configuration,fast charge/discharge response,high power output,and long service life（>100,000 cycles）,SCs are shown in the next generation of energy technology Broad prospects:wearable electronic devices,fast charging mobile phones,regenerative braking motors,and real-time management of industrial power and energy.However,the practical application of supercapacitors is limited by their lower energy density.It has been proved that constructing asymmetric supercapacitors（ASCs）by combining battery-type Faradic electrodes as energy sources and capacitive electrodes as power sources is an effective strategy to expand operating voltage and increase energy density.However,traditional ASCs mainly operate in aqueous electrolytes,and solvent evaporation and harmful electrolyte leakage will inevitably occur.In contrast,solid-state ASCs（SASCs）with binder-free flexible electrodes and gel electrolytes are the preferred device configuration to meet the flexibility,lightness,wear resistance and high mechanical integrity of portable and future electronic products Requirements.（1）Fluorine-rich and oxygen-rich vacant Ni Mo O₄(F-Ni Mo O_4-x)nanosheet arrays were constructed on carbon fiber cloth（CFC）through convenient hydrothermal and wet chemical reduction processes.The structure and electronic properties of F-Ni Mo O4-x can be effectively adjusted by the synergistic effect of F doping and O vacancies,thereby increasing the conductivity and enhancing the Faraday redox reaction.The obtained flexible F-Ni Mo O_4-x@CFC is tested with three electrodes,and the specific capacitance is as high as 2.45 F cm^-2 under the current density of 1 m A cm^-2,which is the original Ni Mo O₄@CFC electrode area specific capacitance(0.38 F cm^-2)More than six times.In addition,the flexible quasi-solid ASCs device has a voltage window of 1.8V,and when the power density is 1790μW cm^-2,the energy density is as high as 336.5μWh cm^-2.It can also achieve an ultra-long and stable life（over 10,000cycles）with a capacity retention rate of 85.7%.（2）A parallel array of P-doped Ni Mo O₄(P-Ni Mo O_4-x)nanowires is grown on carbon fiber cloth（CFC）through hydrothermal reaction and subsequent phosphating.The phosphating process also introduces oxygen vacancies on the surface of the Ni Mo O₄nanowires.It can promote the mass transfer efficiency and surface wettability of the electrolyte/gas,thereby effectively avoiding the"dead volume"of the active material.On the other hand,the surface doped with anions and oxygen-rich vacancies can promote electron transfer and provide sufficient active sites,thereby improving the utilization and reactivity of active materials.The optimized P-Ni Mo O_4-x electrode can provide an area specific capacitance of 0.74 F cm^-2 at a current density of 1 m A cm^-2,which is almost twice that of the original Ni Mo O₄.In addition,the assembled flexible quasi-solid P-Ni Mo O_4-x@CFC//AC@CFC has a high energy density of 228.8μWh cm^-2when the power density is 1217.2μW cm^-2.It can also achieve an ultra-long and stable life（over 10,000 cycles）with a capacity retention rate of 85.3%.