Construction And Electrocatalytic Performance Of Transition?Metal Doped Tungsten?Based Materials

Zinc-air battery is one of the representatives of high-efficiency energy conversion devices.High-efficiency zinc-air batteries play a key role in portable electronic devices and electric vehicles,which can reduce the demand for fossil fuels.In zinc-air batteries,the oxygen reduction reaction?ORR?is one of the basic reactions related to the efficiency of the battery.However,the slow kinetics of ORR severely hinders the application of zinc-air batteries.Therefore,it is necessary to find efficient and stable catalysts to reduce the activation energy of the ORR reaction and improve the energy conversion efficiency of zinc-air batteries.Currently,platinum-based catalysts are commonly used ORR catalysts.However,the poor stability and high cost of platinum-based materials have severely restricted the long-term commercial development of zinc-air batteries.Therefore,in order to develop ORR non-precious metal electrocatalysts with long-term stability,low cost and high catalytic activity,many efforts still need to be made.Among non-precious metal catalysts,tungsten-based catalysts are a very promising candidate.Tungsten has a variety of compounds,including tungsten oxide,tungsten carbide,tungsten sulfide,tungsten nitride,tungstate,etc.Their respective characteristics in terms of electrochemical properties provide a very wide range of options for constructing tungsten-based oxygen reduction catalysts.Most tungsten compounds have very stable chemical properties,which has great significance for the development of long-term stable oxygen reduction catalytic materials.In this paper,tungsten carbide and tungstate with excellent stability are selected as the electrocatalysts.The electronic structure of the tungsten-based material can be adjusted by the transition metal doping.The transition metal doping can improve the catalytic efficiency.The d-orbital multi-electron transition metals can adjust the electronic structure of d-orbital-deficient tungsten-base materials,reduce the energy barrier of oxygen reduction reaction,and improve the catalytic efficiency.The main research contents of this paper are as follows:?1?Graphitic carbon nitride and bacterial fiber gel were used as template,nitrogen source and main carbon source,respectively.The tungstic acid in ammonia and ferric chloride solution dissolved were used as metal sources.The aerogel with sponge-like porous structure was obtained by freeze-drying bacterial fiber gel.Then,the FeWO₄/nitrogen-doped graphene electrocatalysts with many microporous structures can be obtained by rapidly carbonized the aerogel.The electrocatalysts not only inherited the advantages of high stability of tungsten-based materials,but also successfully solved the problem of low intrinsic activity of tungsten-based materials.The FeWO₄/nitrogen-doped graphene showed excellent catalytic performance comparing to the material without introducing transition metals?W/NC?.?2?The metal tungsten tended to form an oxide during the calcination process.The metal tungsten was converted into tungsten carbide in the rich carbon environment.Based on?1?,the graphene oxide was introduced to provide the rich carbon environment.And,cobalt entered the tungsten carbide crystal lattice through embedding,which effectively changed the crystal structure of the tungsten carbide,thereby optimized its electronic structure and successfully improved the catalytic activity.At the same time,work?2?proves that transition metals with different electronic arrangement can also improve the performance of tungsten-based materials.Based on the synthetic cobalt-doped tungsten carbide catalyst,a simple zinc-air battery was assembled,which showed excellent performance and long-term cycle stability.?3?Based on the?2?,two transition metals were used to adjust the tungsten carbide.Compared with single transition metal,two transition metals had more flexible adjustment space to achieve an optimized electronic structure and provide closeness possibly optimal value of catalytic activity.Finally,the oxygen reduction catalyst with excellent electrocatalytic activity and stability was obtained.The zinc-air battery was assembled with the above catalyst,which had more excellent stability and activity than zinc-air battery with cobalt-doped tungsten carbide catalyst.