An Application Study Of Perovskite Cathodes For Electrocatalytic Reduction Of Nitrate In Wastewater

The excessive use of nitrogen-containing chemical fertilizers and the discharge of industrial wastewater,which does not meet the required standards,lead to the accumulation of nitrate in surface water and groundwater.This results in the destruction of water ecology and poses a serious threat to human health.Among the remediation technologies for nitrate-polluted water,electrocatalytic reduction has gained widespread attention due to its advantages of producing fewer by-products and being environmentally friendly.The electrode materials used in nitrate electrocatalytic reduction play a key role in the process.The development of economical,efficient,and stable electrocatalysts has always been a significant challenge faced by this technology.In recent years,perovskite oxides,with abundant reserves and low prices,have shown promising catalytic activity in the fields of carbon dioxide reduction reaction（CO₂RR）and nitrogen reduction reaction（NRR）due to their flexible and controllable composition and structure.Inspired by this,the application of perovskite oxides in nitrate electrocatalytic reduction can open up a new way for the development of catalysts.In this paper,a series of perovskite oxides La MO_3-δ（M=Fe,Co,Ni,and Cu）were prepared using the sol-gel method to explore the feasibility of their catalytic reduction of nitrate,and the influence of various factors on the performance of the catalytic reduction was investigated.Then,the reaction mechanism of perovskite electrocatalytic reduction of nitrate was explored,and the performance of perovskite in the treatment of actual wastewater was verified.To improve the catalytic reduction efficiency of nitrate and convert it into ammonia,the final product with important application value,we selected perovskite oxide BiFeO₃ as the research object.We realized efficient electrocatalytic ammonia production of nitrate by using the in-situ electrochemical reconstruction method.Combining physical and chemical properties characterization,electrochemical performance testing,and density functional theory calculation,we studied the changes of active sites caused by the in-situ electrochemical reconstruction method of perovskite and the mechanism of promoting the improvement of ammonia production efficiency.This research provides a new modification strategy for realizing the high efficiency electrocatalytic ammonia production of nitrate of perovskite BiFeO₃ and even most perovskite materials.The study consists of the following two parts:（1）Four perovskite materials La MO_3-δ（M=Fe,Co,Ni,and Cu）were successfully synthesized by the sol-gel method on a porous titanium substrate.Nitrate electrocatalytic reduction experiments showed that the four perovskite oxides prepared had good nitrate catalytic reduction activity.The nitrate removal rate in descending order was La₂Cu O₄（81.1%）>La Fe O₃（66.3%）>La Ni O₃（42.6%）>La Co O₃（34.7%）.We then used La₂Cu O₄ as an example to explore the influence of various factors such as nitrate concentration,current density,p H,and chloride ions.This helped us to investigate the application range of perovskite materials in nitrate electrocatalytic reduction.Mechanism analysis showed that Cu（I）-Cu（II）-Cu（I）redox electric pairs and oxygen vacancies in La₂Cu O₄ were active sites for nitrate electrocatalytic reduction.In addition,the perovskite In addition,the perovskite electrode was proved to have good durability through continuous cycle test,and its ability to treat actual wastewater was investigated.The nitrate removal rate was up to 73.6%.These results demonstrate the potential of perovskite oxide as a new catalyst for nitrate electrocatalytic reduction,and open up new directions for the development of electrocatalysts.（2）we focused on BiFeO₃ perovskite as our research object,and explored an in-situ electrochemical reconstruction method for increasing its active site density,with the aim of promoting efficient ammonia production from nitrate.We compared the characterization of BiFeO₃ before and after reconstruction using XRD,SEM,HR-TEM,XPS,and EPR,and found that a new substance,elemental Bi,was formed on the surface of BiFeO₃,and that the concentration of oxygen vacancy increased（from 23.2%to 36.0%）.Secondly,We used in-situ differential electrochemical mass spectrometry（DEMS）tests and density functional theory（DFT）calculations to investigate the effect of Bi elemental and oxygen vacancy on nitrate reduction.We found that they acted as active sites that promoted the adsorption of nitric acid,with the adsorption energy decreasing from 0.75 e V to 0.68 e V,and accelerated the rapid conversion of NO₂ to NO.Finally,we analyzed the promoting effect of perovskite structure evolution on nitrate reduction,and provided new insights for the rational design of perovskite electrocatalysts and a new modification strategy for further improving the catalytic reduction efficiency of perovskite materials...