Synthesis Of Copper-based Catalyst And Its Performance In Electrocatalytic Nitrate Reduction To Ammonia

Ammonia(NH3)is an essential chemical product for human production and life.It can be made into urea for use in agriculture,as a refrigerant in industry,and even in the defense industry,where ammonia is an important ingredient in rocket propellant.However,since the advent of ammonia synthesis technology for more than a century,human beings still use the Haber-Bosch process requiring high energy consumption and high CO2 emission,and today the world is facing global warming,energy crisis and other severe challenges.Therefore,it is urgent to seek a new kind of green and sustainable ammonia production under environmental conditions to replace the traditional synthetic ammonia technology.Compared with other emerging ammonia synthesis technologies,electrocatalytic nitrate reduction of ammonia technology has unparalleled advantages,with a wide range of nitrogen sources,high solubility,water as proton source,green renewable resources electricity as power.The most important thing is that it can produce ammonia at a high rate at normal temperature and pressure.The rate of ammonia production mainly depends on the catalytic performance of the catalyst.Therefore,the design and preparation of efficient and stable catalyst is the key to achieve ammonia synthesis at room temperature instead of the traditional Haber-Bosch process.About this study,this thesis designed two kinds of catalysts for high efficiency electrocatalytic synthesis of ammonia under environmental conditions,mainly including the following contents:1.Cu2Ag2O3 nanowire synthesized by liquid phase reduction method was electrochemical reduced into CuAg alloy nanowires catalyst by two-step method.SEM and TEM results showed that the morphology of Cu2Ag2O3 nanowire did not change after electrochemical reduction.The conversion of Cu2Ag2O3 to CuAg solid solution alloy was proved by XRD and EDS spectra.The NitrRR performance test showed that the catalyst had a high Faraday efficiency of 95.01%at-0.7 V vs.RHE potential,and the NH3 yield reached 1474.81 μg h-1 mgcat-1 with a selectivity of 86.98%.The XPS characterization of the catalyst before and after the reaction proved that the high activity came from Cu+ as the active center,which realized the electron transfer of Ag and Cu,and the presence of Cu inhibited the occurrence of hydrogen production in the side reaction.2.The Au-doped Cu nanowires catalyst was prepared on the copper foam electrode by the simple three-step method of liquid phase reduction,annealing and electrochemical reduction,and was applied to the selective nitrate electroreduction to ammonia experiment.SEM and TEM results showed the morphology of nanowires.XRD and XPS characterizations demonstrate the successful doping of Au.The results of electrochemical experiments showed that the NH3 yield of Au-Cu NWs/CF NitrRR was 5336.0±159.2 μg h-1 cm-2 and the Faraday efficiency was 84.1±1.0%at the neutral potential of-1.05 V vs.RHE.Through XPS characterization of the catalyst before and after the reaction,it was found that the doping of Au resulted in the electron transfer between Au and Cu and the existence of a large number of oxygen vacancies in the material.These characteristics reduced the NitrRR reaction energy barrier of the catalyst,making the material have a good performance of electrocatalytic nitrate reduction of ammonia.