Construction Of Cu-Pd-Based Catalysts And Investigation In The Electrochemical Reduction Of Ammonia From Nitrate

With the rapid development of agriculture and industry and the continuous improvement of people’s living standards,the discharge of industrial wastewater and domestic sewage is also showing an increasing trend,and the application of nitrogen fertilizers in agricultural production is also increasing,making the nitrate nitrogen pollution in water more and more serious,which is directly related to human health,social stability and economic development.In response to the current nitrate pollution problem,scientists have researched a series of water treatment technologies,among which electrocatalytic reduction technology stands out for its green and economic advantages,among which the electrocatalytic reduction of nitrate to ammonia（NRA）route has attracted widespread attention.On the other hand,ammonia as a green energy source can play a greater economic value,this"waste to treasure"idea is a good water treatment technology alternative ideas.In this work,we propose to combine electrochemical deposition and in situ growth synthesis strategies to design and prepare three kinds of adjustable copper and nickel-based alloy catalysts,aiming to use the synergistic effect of metal components to promote the adsorption and activation of nitrate and inhibit the HER activity to improve the selectivity and Faraday efficiency of ammonia synthesis by NRA electrocatalysts.Mapping,HAADF,XPS to characterize the structure and surface composition of the catalysts,optimize the structure of the catalysts by metal salt ratio and preparation methods to enhance the electrocatalytic performance of NRA,and establish a conformational relationship between the structure of the catalysts and the electrochemical performance of the catalytic reduction of nitrate for ammonia synthesis.The research contents of this project are as follows.1.system I was mainly obtained by in situ growth method through the substitution reaction of copper metal,and Pd_0.5@CF was obtained from Pd-incorporated copper electrode.after exploring the influencing factors of loading concentration,reaction time and reaction voltage of metal Pd,the impregnation concentration of 0.5 mg/ml Pd Cl₂was chosen for the preparation of electrode,the best electrocatalytic reaction time was 3 h,the best reaction voltage was-0.23 V vs.The Pd_0.5@CF catalyst was suitable for the reduction of nitrate at medium to high concentrations,but not for the reduction of nitrate at high concentrations.88%ammonia selectivity was achieved for the catalytic reduction of nitrate to ammonia in a 1 M KOH solution containing 800 ppm nitrate.After five IT cycles of experiments,the ammonia production rate decreased from 0.666 mmol h-1 cm^-2to 0.552 mmol h^-1cm^-2,and the nitrate removal rate only decreased by about 4%,indicating the good stability of the catalyst.2.In system II,we prepared a modified Cu₁Pd₁@CF catalyst for the metal agglomeration on the surface of Pd_0.5@CF catalyst.The catalysts were prepared by in situ growth method by regulating the concentrations of copper and palladium salts and choosing 0.75 mg/ml Pd Cl₂,0.75 mg/ml Cu Cl₂salt solution for Cu₁Pd₁@CF catalyst.The modified Cu₁Pd₁@CF foam is suitable for the reduction of nitrate at concentrations below 1000 ppm.In a 1 M KOH solution containing 1000 ppm nitrate,the selectivity of Cu₁Pd₁@CF for the product ammonia is 90%,the nitrate removal rate is nearly 100%,and the Faraday efficiency is 97%.The ammonia production rate decreased from 0.902 mmol h^-1cm^-2to 0.815 mmol h^-1cm^-2with only 150 C decrease in power,indicating that the catalyst has more stable performance than Pd_0.5@CF.3.System III achieves the goal of preparing NRA catalysts with good performance by modulating the components of the multi-metals and the choice of substrates.The best morphology is Cu₁Pd₁@Ni foam catalyst,which is observed by SEM,TEM,HRTEM characterization as Cu₁Pd₁@Ni foam catalyst with special dendritic morphology and good electrochemical properties.Nitrate solution,the product ammonia conversion is 64%,nitrate conversion is nearly 100%,and Faraday efficiency is 70%.In the stability experiments of Cu₁Pd₁@Ni foam we found that after six NRA processes,the nitrate removal rate only decreased by 5%,the product ammonia conversion remained around 65%,and the Faraday efficiency was also around 65%,indicating that the catalyst performance remained stable and steady during the catalytic process in 18 hours.Through the study of the component modulation of the multi-metal and the selection of the substrate we found that the synergistic effect of copper-palladium in the catalytic reduction of nitrate was better than the catalytic effect of copper and palladium monometallic,and the synergistic effect of copper-palladium was beneficial to improve the conversion of copper nitrate;copper metal showed higher selectivity to nitrite,so Cu foam in the reaction of nitrate reduction to generate nitrite showed better reactivity,while nickel metal showed better removal of nitrite.The high yield of the target product ammonia requires that the catalyst must increase the conversion of nitrate nitrogen and decrease the conversion of nitrite nitrogen in the NRA process.Combining the previous effects of different metal components and substrates on nitrate and nitrite nitrogen.Combining the effects of different metal components and different substrates on nitrate and nitrite nitrogen,combining the previous effects of different metal components and different substrates on nitrate and nitrite nitrogen,we should choose nickel as the substrate,containing copper and palladium metal,and to control the content of copper metal as low as possible in order to achieve the highest yield of ammonia,so Cu₁Pd₁@Ni foam in the process of electrocatalytic reduction of nitrate synthesis of ammonia Therefore,Cu₁Pd₁@Ni foam showed good electrochemical activity in four aspects:nitrate removal,nitrite conversion,ammonia production and Faraday efficiency.By investigating the effect of component modulation of the multi-metal and the choice of substrate on the NRA catalysts,we have selected the best performing catalysts,and this method facilitates the preparation of more NRA catalysts with good morphology and good performance.