Design Of Cobalt-based Composite Oxide Nanocatalyst And Study On Its Electrocatalytic Performance For Ammonia Synthesis

Ammonia（NH₃）is one of the most productive chemicals in the world,plays a vital role in many fields.With the development of basic research and engineering technology in the field of electrochemical energy conversion,compared with the traditional Haber-Bosch industrial ammonia synthesis,electro-catalytic ammonia synthesis has become a new goal of the scientific community.However,electrocatalytic synthesis of ammonia is still limited by the problems of low ammonia yield,low Faraday efficiency,low current density and high over potential.Therefore,the design of catalyst materials with high catalytic activity and high selectivity is a key factor in the development of electrocatalytic ammonia synthesis technology.In order to improve the catalytic activity of the catalyst,the cobalt-based oxides with high specific capacity and high specific capacitance were selected as the main materials of the catalyst.The stability and electrical conductivity of catalyst materials can be improved by introducing chemical property active and cheap elements into monometallic oxides to form bimetallic oxides.Cobalt-based oxides prepared using MOFs as templates can maintain some of the characteristics of MOFs,such as element doping and loading of porous carbon,it is a feasible method to improve the specific surface area of catalyst and to expose more active sites in electrolyte.Using conductive substrate（Carbon Paper,Foamed Nickel）can improve the low conductivity between the electrocatalyst and the electrode substrate in the electrocatalysis process,so as to further improve the catalytic performance.1.The cobalt-manganese layered bimetallic hydroxide（MnCo-LDH）grown on carbon paper was used as the precursor,and ZIF-67 as the nitrogen source,Mn_xCo_3-xO₄ Nitrogen-doped Porous Carbon（NPC）composite catalysts were prepared by a simple hydrothermal-in-situ growth method,and the effects of Mn-doped and Nitrogen-doped Porous Carbon loading on ENRR performance were investigated.In0.1 mol L^-1 Na₂SO₄ solution,when the complex catalyst is at-0.2 V（vs RHE）,the highest ammonia yield can reach 3.81×10^-11 mol s^-1 cm^-2 and the Faraday efficiency can reach 5.44%,Mn_xCo_3-xO₄/NPC also showed good electrochemical properties and structural stability.2.The cobalt-copper layered bimetallic hydroxide（CoCu-LDH）grown on nickel foam was used as the precursor for oxidation in air and annealing reduction in argon-hydrogen mixture,the Cu-doped Co/Co O heterostructure composite catalyst was prepared.In the electrocatalytic reduction of nitrate to ammonia,copper has a unique3d electron orbital,which can promote the electron transfer between the catalyst and the reactant,and the electron deficient Co can inhibit the hydrogen evolution reaction,improved Faraday efficiency and ammonia selectivity in the reaction.The results show that the prepared Cu/Co/Co O heterostructure catalyst has excellent performance in Faraday efficiency（90.66%）,selectivity（84.85%）and yield(140.27μmol h^-1 cm^-2)of-0.4 V（vs RHE）.