Preparation Of Copper-based Catalyst And Research Of Their Electrocatalytic Performance For Nitrate Reduction To Ammonia

Excessive nitrate ions in the environment break the natural nitrogen cycle and become a significant threat to human health.Meanwhile,ammonia is a versatile compound that can be used as fertilizer,chemical,or fuel.However,the conventional Haber-Bosch ammonia synthesis loop suffers from harsh process conditions,high energy consumption,and heavy pollution.In contrast,electrocatalytic nitrate reduction is mild and green,which can not only remove nitrate harmful to the environment and human body,but also produce value-added chemicals such as ammonia,which provides a sustainable alternative for the Haber-Bosch process and is of great significance.However,the competitive hydrogen evolution reaction and eight-electron transfer process lead to low Faraday efficiency and ammonia selectivity.Therefore,it is especially important to develop and design high-activity electrocatalysts.Copper（Cu）has aroused extensive research because of its unique d-orbital electronic configuration and the advantages of abundant reserves and low price.However,the passivation or metal species leaching of copper-based materials during long-term operation and the weak adsorption of H on Cu surface greatly limit its application in electro-catalytic nitrate reduction of synthetic ammonia（NRA）.Based on this,two kinds of copper-based catalysts with high selectivity and stability were prepared by heteroatom doping and interface engineering strategy,and their NRA properties and the internal relationship between catalyst structure and catalytic activity were studied.Its main contents include the following two aspects:（1）An efficient boron-doped copper nanowire electrocatalyst,B-Cu NWs/CF,for the NRA was successfully synthetized.The incorporation of electron deficient boron atoms into copper nanowires resulted in the electron localization with the partially empty Cu3d orbitals and improved significantly the catalytic activity of Cu active sites.The FE,nitrate conversion rate,the ammonia selectivity,and yield rate for the NRA catalyzed by B-Cu NWs/CF achieved 94.41±0.12%,100.02±0.94%,96.58±1.5%,and 0.276±0.00296 mmol·h^-1·cm^-2,respectively,remarkably superior to those of the pristine Cu NWs/CF and most of recently reported copper-based catalysts.In addition,the FE,NO₃^-conversion rate,NH₃selectivity and yield rate of B-Cu NWs/CF have no obvious attenuation after 14 cycles,showing excellent stability.The DFT calculations confirmed that the incorporation of boron into copper nanowires effectively inhibited the hydrogen evolution and the production of other reaction by-products.Importantly,the incorporation of boron significantly enhanced the adsorption of the^*NO₃intermediate on the copper surface and greatly reduced the activation barrier of*NO→*HNO,which promoted the production of ammonia.（2）Ni₂P@Cu₃P nanoarrays（Ni₂P@Cu₃P/CF）with heterogeneous interfaces were successfully synthesized in situ on copper foam substrate（CF）by three-step synthesis method.The directional movement of electrons in Ni₂P@Cu₃P/CF promotes the redistribution of charges at the heterogeneous interface of phosphide,which can adjust the electronic structure of catalyst and change the adsorption energy of reactants and intermediates on active sites,thus promoting the reaction kinetics.In addition,the formation of heterogeneous array and thin edge structure provide more active sites.At-0.49 V vs.RHE,the FE,nitrate conversion rate,the ammonia selectivity,and yield rate for the NRA catalyzed by Ni₂P@Cu₃P/CF achieved,96.97±0.28%,99.35±0.31%,98.07±0.75%,and 0.2784±0.0022 mmol·h^-1·cm^-2,respectively,which showed excellent performance.At the same time,after 14 consecutive cycle tests,Ni₂P@Cu₃P/CF still has high activity and excellent stability.