Preparation And Electrochemical Properties Of Molybdenum Compound Electrode Materials For Supercapacitors

Supercapacitors(SCs)are a kind of energy storage devices with great potential.They have unique advantages in cycle life,power density,operating temperature range and charge and discharge cycle,etc.,and have been widely used in various fields such as automobile industry,energy collection and power grid stability.Among all the key components of supercapacitor devices,the design and research of electrode materials play an important role in the electrochemical storage performance.Among them,molybdenum fund materials have been widely concerned for their high theoretical capacity,many oxidation states,low cost and abundant natural resources.The electrochemical performance of the device can be improved more effectively by the electrode material with double electric layer and pseudo capacitance storage mechanism.Therefore,the design process,morphology control and electrochemical performance of molybdenum-based materials as SCs electrode materials were discussed in this paper.In this paper,Mo2N and MoC materials were prepared without the use of dangerous gases.N,O codoped carbon sheets composite(Mo2NNPs/NOCS)were prepared by electrostatic self-polymerization of molybdenum nitride nanoparticles on the surface of protonated C3N4 and molybdate ions.Subsequently,various types of molybdenum carbide materials were obtained by gradient carbonization through in situ carburizing reduction method,and the unique structure of molybdenum carbide/carbon hollow microtubule composites(MoC/CHMT)was prepared by adjusting the ratio of carbon sources to control the crystal transformation.At the same time,the design process,m orphology control and electrochemical properties of molybdenum foundation compounds as SCs electrode materials were discussed.The main research contents were as follows:1.The Mo2N electrode materials in acid electrolyte urgently need to make progress in supercapacitors.The molybdenum nitride nanoparticles embedded in N,O co-doped carbon sheets composite(Mo2NNPs/NOCS)are fabricated via Mo2N nanoparticles in situ growth on the surface of selfsacrifice C3N4.The results show that small size Mo2N nanoparticles in ranged from 1.2 to 1.5 nm are distributed uniformly and embedded in the surface of carbon nanosheet materials.The effects of the temperature and ratio of ammonium molybdate tetrahydrate to C3N4 on electrochemical performance are investigated in detail.The optimum sintering temperature of Mo2NNPs/NOCS was 800℃,and the optimum blending ratio of ammonium molybdate tetrahydrate and C3N4 of Mo2NNPs/NOCS-800 was 1:10.The maximum specific capacitance could reach 294 F g-1 at 0.5 A g-1 after optimization.Further,the supercapacitor device is assembled with a commercial activated carbon YP50 as positive electrode in acid electrolyte,delivering a high energy density of 13.6 Wh kg-1.2.We report the synthesis of pure phase molybdenum carbide(MoC)nanoparticles via the in-situ carburization reduction route without using any reducing agent.Dopamine hydrochloride monomer is sequentially polymerized on Mo-MOF nanorods as a template,and multiple types of layered molybdenum carbides(α-MoC,η-MoC and β-Mo2C)were obtained by gradient carbonization.The surface crystal phase changes with the change of dopamine hydrochloride,and the electrochemical performance of αMoC materials is better than that of other crystalline molybdenum carbide materials.In addition,with the increase of temperature,the central rod-like Mo-MOF gradually disappears,forming a mid-empty shell structure,which is conducive to the full contact between the electrolyte and the electrode material.The effects of temperature and C source content on electrochemical performance are studied.At a large potential window of 1.3 V,the molybdenum carbide/carbon hollow microtubes composite(MoC/CHMT)electrode material has a specific capacitance of 513.5 F g-1 at a current density of 0.5 A g-1.In addition,the MoC/CHMT//YP50 device obtains the maximum power density of 6988 W kg-1 at the potential window of 0-1.4 V and the energy density of 4.5 Wh kg-1.And the retention rate reached 130%after 10000 ultra-long cycles under the potential window of 0-1.2 V.The maximum energy density of YP50//MoC/CHMT device is 17.5 Wh kg-1 at the potential window of 0-1.4 V.