Application Of Nickel-based Anode Catalysts In Urea Fuel Cells

In recent years,a large amout of urea-rich wastewater from the fertilizer industry,animal or human urine is discharged to the surrounding environment,the conversion of urea to ammonia in the natural environment will lead to eutrophication of water bodies.Urea can lead to eutrophication of water bodies during its natural conversion to ammonia.At present,the main ways of urea decomposition are biological decomposition,thermal hydrolysis and chemical oxidation.However,these methods require the use of complex equipment,which limits their wide application.Urea-fueled fuel cells,known as direct urea fuel cells(DUFC),convert chemical energy directly to electricity.Under alkaline conditions,the anodic products of urea oxidation are non-toxic carbon dioxide and nitrogen gas.Therefore,direct urea fuel cell provides a new idea and method for treating urea-rich wastewater.Due to the slow anodic oxidation reaction kinetics of urea,the power density of DUFC is lower than that of polymer electrolyte membrane fuel cells under the same conditions.In order to improve the performance of direct urea fuel cells,many researchers have focused on the design and syfhesis of electrode catalysts with good activity and long-term stability.Nickel-based catalysts are favored by researchers because of their low oxidation overpotefial and high oxidation activity.In order to increase the active sites on the electrode surface and the specific surface area of the catalyst,the catalyst components are often loaded on porous nanomaterials,such as metal foams and carbon-based materials.Among them,carbon material is widely used as conductive substrate because of its good conductivity and stability.However,due to the relatively weak interaction between the carbon substrate and the active component of the catalyst,the surface of the carbon material can be modified by doping heteroatoms(P,S,N)to improve the force between the substrate surface and the active site,and make the crystal phase of the catalyst tend to be stable.Therefore,using simpler and more convenient methods to prepare carbon nanomaterial catalysts doped with other atoms is both an opportunity and a great challenges.Polyacrylonitrile(PAN)not only can be used as carbon and nitrogen source,but also the catalytic raw material is easy to obtain,the syfhesis method is quick and simple,the yield is large,the durability is good,the storage capacity is high,the density is low.Therefore,in this paper,the electrospinning method was used to syfhesize polyacrylonitrile polymer fiber doped with nickel base catalyst,and the nickel base composite was successfully prepared by high temperature carbonization method,and the electrocatalytic performance and structure-activity relationship of nickel matrix composites were studied.This thesis mainly includes the following three aspects:(1)Polyacrylonitrile-nickel fiber membranes were prepared by electrostatic spinning process,after pre-oxidation to make it stable,after carbonization(oxygen atmosphere)to prepare catalyst.The catalyst with good performance was obtained by optimizing the syfhesis conditions.The experimental results show that the current density of the best CNF-Ni-3 catalyst can reach 617 m A·cm^-2at 0.6 V(vs Ag/Ag Cl)working voltage in alkaline medium.Meanwhile,CNF-Ni-3 also showed good stability after 10000 seconds of stability test(capacitor retention 68%).(2)On the basis of the one work,CNF-Ni₁Co₂ catalyst with excellent performance was obtained by optimizing the preparation conditions by doping cobalt in the precursor solution of electrostatic spinning.The experimental results show that the doping of cobalt contributes to the conversion of nickel hydroxide to nickel oxyhydroxide,thus increasing the active site of Ni catalytic reaction,improving the current density and stability of electrocatalytic oxidation of urea,and reducing the initial potential.The current density of CNF-Ni₁Co₂catalyst can reach 734 m A·cm^-2at 0.6 V(vs Ag/Ag Cl)working voltage in alkaline medium.At the same time,the stability test after 10000 seconds also showed good stability(capacitor retention80%).(3)On the basis of the second work,CNF-(Co,Ni)₉S₈ catalyst with excellent performance was obtained by optimizing the synthesis conditions and using nitrogen in the carbonization process.The experimental results show that the best CNF-(Co,Ni)₉S₈catalyst can further reduce the initial potential of nickel-based catalysts catalyzed urea,and has higher current density and better time stability.