Synthesis Of Nickel-based Catalysts For Electro-oxidation Of Urea

The urea electro-oxidation reaction can effectively solve the issues of environmental pollution and energy shortage,therefore worldwide attention has been paid by scientists.However,owing to the sluggish kinetics and high overpotential caused by large amount of electron transfer in the urea electro-oxidation processes,suitable catalysts are deserved for enhancing the performance of urea electrooxidation.Among various types of catalysts,nickel-based catalysts show promising application in urea electro-oxidation.Since the catalytic performance of catalysts is greatly affected by their morphology,structure and surface chemical properties,catalysts with well designed and regulated morphology,structure and surface chemical properties will have excellent catalytic performance towards urea electro-oxidation.In this paper,various nickel-based catalysts were synthesized using different methods and their morphology,structure and surface chemical properties are tuned.The catalytic performance of these nickel-based catalysts towards urea electro-oxidation were then investigated,which will be described as follows,1.Ni Mo O₄ nanoparticles embedded in nanoporous carbon nanosheets derived from peanut shells:efficient electrocatalysts for urea oxidation.Introducing the Mo species and carbon materials into nickel-based materials may solve the problems of the toxicity,aggregation and poor conductivity.Ni-Mo/C based bimetallic materials have been introduced.Ni Mo O₄ nanoparticles were then embedded in C_psvia a facile impregnation method.Compared with the Ni Mo O₄ nanoparticles,the as-prepared catalyst possessed large surface area and the embedded Ni Mo O₄nanoparticles exhibited small size with average diameter of 10 nm and exposed more active centers.The chemical properties of Ni Mo O₄ could be also tuned after embedded in C_ps.The anodic oxidation peak current density of NMO_0.3/C_ps(394 m A·cm^-2·mg^-1)was 21.9 times larger than NMO by cyclic voltammogram measurements,which shows again that the introduction of Mo species and carbon materials into nickel-based materials can improve the catalytic performance.2.Synthesis of carbon-modified nickel phosphide catalysts for the urea electro-oxidation reaction.The full exposure of active sites is helpful to the improvement of catalytic performance,and is of great significance to prepare catalysts with special morphology.A series of carbon-modified nickel phosphide catalystswith different morphology and structure are synthesized by hydrothermal method and calcination treatment,among which peanut shell is used as carbon source.The results show that the crystal structure of nickel phosphide and the properties of carbon materials are affected by the calcination temperature.The results show that Ni-P-C possesses high catalytic activity andkinetics at 700^°C.And the Tafel slope is22 m V·decade^-1 and the urea oxidation current density is 565 m A·cm^-2·mg^-1 in 1 M KOH with 0.33 M urea,and the anodic oxidation peak current density of Ni-P-C was 4.85 times larger than Ni-P(116.4 m A·cm^-2·mg^-1),which shows again that the calcination temperature could well tune the structure and the properties of Ni-P-C.3.Synthesis of the La Ni_xCo_1-xO₃ catalyst via sol-gel method for urea electro-oxidation.Atomic-doped could effectively improve the catalytic performance.It is of great significance to study how heteroatoms can be introduced into the structure.The type of ABO₃catalysts are prepared by sol-gel method using Co as dopants.The results showed that the lattice structure of La Ni O₃ can be changed by Co element simultaneously,while Co element is supported on the surface of catalyst in step synthesis.The Tafle slope of LNCO_0.1 catalyst is39 m V·deccade^-1,and the maximum peak current density is 498.6 m A·cm^-2·mg^-1,and the anodic oxidation peak current density of LNCO_0.1 is 8.5 times larger than LNO-C_0.1(116.4m A·cm^-2·mg^-1)in 1 M KOH with 0.33 M urea.The results test show that the catalytic activity and reaction kinetics of Co element are better than that of Co element on La Ni O₃ surface when they are introduced into the corresponding lattice.