Design, Synthesis And Electrochemical Applications Of Vanadium-based Nitrogen (oxygen) Compounds

Environmental and energy issues have forced scientists to develop efficient energy conversion and energy storage devices.Transition metal-based materials have attracted the attention of researchers because of its rich and variable structure.Vanadium has many advantages such as abundant reserves,variable price,low price and high stability,making it a promising catalyst/energy storage material.However,the performance of vanadium compounds alone（phase）are relatively low,which need to be improved by morphological regulation,heterogeneous structure and carbon composite.Based on the above analysis,the main contents of this paper include the following three aspects:1.NH₄VO₃ and C₂H₄N₄ were used as raw materials.The precursor material was synthesized by liquid phase evaporation and then further heat-treated in a nitrogen atmosphere.The composite materials having porous structure of vanadium nitride（VN）and N-doped carbon（NC）was obtained.The experimental results show that the composition and morphology of composite materials can be effectively controlled by controlling the feed ratio and calcnation temperature.The VN@NC composite material synthesized by this method can be used as electrode material for highly efficient and stable supercapacitor.The material had high discharge specific capacitance,and the current density is 0.5 A g^-1,which is 268 F g^-1,and has good cyclic stability.2.V₂O₅ and Co（NO₃）₂·6H₂O were selected as vanadium source and cobalt source respectively,through hydrothermal-reassembly method,after ammonia reduction and nitriding,the cobalt-vanadium bimetallic composite with porous ribbon structure was successfully prepared.The controllable preparation of bimetallic materials was realized by adjusting the ratio and temperature.The composite materials prepared by the method can be used as an electrocatalytic overall water splitting catalyst.Co-V-6 has better HER catalytic activity and Co-V-5 has better OER catalytic activity,both of them were used as the cathode and anode for the water splitting test respectively,showed good catalytic activity,when the current density is 10 mA cm^-2,the voltage can reach 1.79 V with good stability.3.Based on the previous research,it was found that the composite materials of early and late transition metals have great potential in water splitting.The flake cobalt-vanadium bimetal composite was further synthesized as an efficient overall water splitting catalyst.The Co₂V₂O₇·xH₂O nanoplates containing both Co and V elements were selected as the precursors.After the calcination under NH₃ atmosphere,the Co2VO4 and Co/VN could be obtained just by tuning the calcination temperature.When the Co₂VO₄ and Co/VN were used as the anode and cathode in a two electrode system,respectively,the cell needed a voltage of 1.65 V to achieve 10 mA cm^-2 together with excellent stability.