Energy Storage Mechanism of Vanadium Nitride via Intercalating Different Atomic Radius for Expanding Interplanar Spacing

As a promising anode material in supercapacitors,vanadium nitride has been widely concerned due to its ultra-high theoretical specific capacitance.However,its routine test capacitance value is still far from the theoretical value and its energy storage mechanism is controversial.In order to solve these two key problems,here we prepare interplanar spacing expanded vanadium nitride materials with different impurity atoms intercalation from two anionic precursors of vanadium-based metal organic frameworks with different functional groups.The obtained vanadium nitride reaches a higher specific capacitance;and further,through ex situ X-Ray diffraction and in situ Raman,the charge storage of vanadium nitride is contributed by two processes:the first benefit is from the K^(+) de/intercalation in the interplanar spacing,and the other one is derived from the redox reaction with OH−by adsorption on surface.Furthermore,both of the first principle calculation and extended experiments support this idea.We believe that such detailed research on the energy storage mechanism can provide a clear idea for the application of metal nitrides in supercapacitors and other energy storage devices.

Vanadium metal-organic framework-derived multifunctional fibers for asymmetric supercapacitor,piezoresistive sensor,and electrochemical water splitting

Fiber-shaped integrated devices are highly desirable for wearable and portable smart electronics,owing to their merits of lightweight,high flexibility,and wearability.However,how to effectively employ multifunctional fibers in one integrated device that can simultaneously achieve energy storage and utilization is a major challenge.Herein,a set of multifunctional fibers all derived from vanadium metal-organic framework nanowires grown on carbon nanotube fiber(V-MOF NWs@CNT fiber)is demonstrated,which can be used for various energy storage and utilization applications.First,a fiber-shaped asymmetric supercapacitor(FASC)is fabricated based on the CoNi-layered double hydroxide nanosheets@vanadium oxide NWs@CNT fiber(CoNi-LDH NSs@V2O5 NWs@CNT fiber)as the positive electrode and vanadium nitride(VN)NWs@CNT fiber as the negative electrode.Benefiting from the outstanding compatibility of the functional materials,the FASC with a maximum working voltage of 1.7 V delivers a high-stack volumetric energy density of 11.27 mW·h/cm3.Then,a fiber-shaped integrated device is assembled by twisting a fiber-shaped piezoresistive sensor(FPS;VN NWs@CNT fiber also served as the highly sensitive material)and a FASC together,where the highperformance FASC can provide a stable and continuous output power for the FPS.Finally,the S-VOx NWs@CNT fiber(sulfur-doped vanadium oxide)electrode shows promising electrocatalytic performance for both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER),which is further constructed into a self-driven water-splitting unit with the integration of the FASCs.The present work demonstrates that the V-MOF NWs@CNTderived fibers have great potential for constructing wearable multifunctional integrated devices.