| The electrochemical catalytic reduction of nitrate nitrogen in liquid phase has attracted much attention recently because of its high controllability,high efficiency and small area of equipment.And the preparation of cathode materials is one of the research hotspots in this field.To achieve the ideal nitrate removal effect,we usually adopt precious metal elements,like platinum(Pt),rhodium(Rh),etc,other than traditional non-precious metal materials,to prepare cathodes.But the former is expensive and difficult to achieve industrial application accordingly.To solve the above contradiction,in this rasearch,two kinds of new efficiency non-precious metal composite electrodes,namely Ti-Sn O2 electrodes and Ti(100-?)Cu? electrodes,were prepared by brush-thermal decomposition method and ectopic electrodeposition method respectively,by using the Ti electrode as the substrate.Scanning electron microscope(SEM),X ray diffraction(XRD)and X ray photoelectron spectroscopy(XPS)were used to analyze the microstructure,phase composition and elemental valence of this two composite electrodes.The electro-catalytic properties,corrosion resistance and the selection characteristics of products of the two composite electrodes were compared through the analysis of the electrochemical characterization and the degradation experiments of liquid nitrate.Finally,this study aims to deeply explore the mechanism of nitrate reduction of these two composite electrodes by combining the results of all the above characterization and analysis.And the main results of this study are as follows:(1)The Ti-Sn O2 cathodes were prepared by brush-thermal decomposition method,whose Sn mole ratios,m,were 0.2 mol/L?0.5 mol/L?0.65 mol/L?0.8 mol/L,respectively.The analysis of SEM,XRD and XPS showed that the active component,Sn O2,were indeed attached to the surface of the Ti-Sn O2 cathodes.But the existence of Sn O2 would cause cracks appear on the surface of the Ti-Sn O2 cathodes,reducing their stability and corrosion resistance,compared with Ti cathode,and the decrease of the corrosion potential of the Ti-Sn O2 cathodes on the Tafel curve can prove this corollary.In addition,excessive Sn O2 would increase cracks on the surface of the Ti-Sn O2 cathodes,and at the same time,visibly heighten their over-potential,which promotes the occurrence of the polarization reaction,which will ultimately affect the selectivity of N2.The results of the electrochemical characterization and the degradation experiments of liquid nitrate showed that,on one hand,the existence of Sn O2 would increase the number of active sites on the surface of Ti-Sn O2 cathodes,thus improving the adsorption activity or the reductive activity,and the reaction rate on NO3-of Ti-Sn O2 cathodes simultaneously,which could increase the nitrate removal ultimately,and the strength of this kind of promotion has nothing to do with the content of Sn O2.On the other hand,the existence of Sn O2 could also improve the adsorption activity and reductive activity on NO2-of Ti-Sn O2 cathodes simultaneously,resulting in no obvious NO2-accumulation during the progress of nitrate reduction,finally advancing the selectivity of N2,realizing the deep degradation of NO3-.(2)The Ti(100-?)Cu? cathodes were prepared by ectopic electrodeposition method,whose Cu mass fractions,?,were 0.02?0.28?1.39?5.65,respectively.The analysis of SEM,XRD and XPS showed that the active component,Cu,were indeed attached to the surface of the Ti(100-?)Cu? cathodes.Moreover,when 0.28<?<1.39,the active component Cu grew on the surface of the Ti(100-?)Cu? cathodes showed(111)preferred orientation,contributing to improving the stability of the Ti(100-?)Cu? cathodes.However,when the value of ? was 5.65,the crystallization of elemental Cu would be restrained so that the stability of the coating would be decreased because of the existence of those excessive copper.In addition,the Tafel curve also showed that an appropriate amount of copper could make the corrosion resistance of the Ti(100-?)Cu? cathodes obviously higher than that of Cu cathode.But excessive copper would make the Ti(100-?)Cu? cathodes present the characteristics of poor corrosion resistance inherent in Cu cathode.At the same time,the results of other electrochemical characterizations and the degradation experiments of liquid nitrate showed that,on one hand,the active component Cu could increase the number of active sites on the surface of electrode,so as to improve the adsorption activity,the reductive activity and reaction rate on NO3-of the Ti(100-?)Cu? cathodes,which could increase the nitrate removal ultimately,and the strength of this positive effect enhanced with the increase of the amount of copper.On the other hand,the existence of the active component Cu would weaken the adsorption activity on NO2-while strengthen the reduction activity on which of the Ti(100-?)Cu? cathodes.And the degree of the enhancement of the reduction activity also enhanced with the increase of the amount of copper,leading to no obvious NO2-accumulation during the progress of nitrate reduction,finally advancing the selectivity of N2,realizing the deep degradation of NO3-.Furthermore,excessive copper could increase the adsorption activity on NO2-of the Ti(100-?)Cu? cathodes though,but it could also decrease the stability of the coating,thereby reducing the selectivity of N2.(3)The analysis of SEM,XRD and XPS on Ti-Sn O2 cathodes and Ti(100-?)Cu? cathodes showed that these two kinds of non-precious metal cathodes were both attached with active components.Besides the Ti(100-?)Cu? cathodes were covered with more active components with no crack,which indicates that the active component Cu was preferably combined with Ti,optimizing the stability of the Ti(100-?)Cu? cathodes.Meanwhile,the analysis on the Tafel curve of these two kinds of cathodes showed that the corrosion resistance of which would be reduced once the active component Sn O2 or Cu was added comparing to Ti cathode,yet the corrosion resistance of the Ti(100-?)Cu? cathodes had a slight advantage between both of which.In the meantime,the results of other electrochemical characterizations and the degradation experiments of liquid nitrate showed that,on one hand,the volt ampere power of the Ti(100-?)Cu? cathodes were far less than that of the Ti-Sn O2 cathodes,also the potential of nitrate reduction peak of which was slightly larger than that of the Ti-Sn O2 cathodes;But the current of nitrate reduction peak and the reaction rate constant was far greater than that of the Ti-Sn O2 cathodes.So overall,the reduction activity on NO3-of the Ti(100-?)Cu? cathodes was much higher than that of the Ti-Sn O2 cathodes,therefore the nitrate removal efficiency of which had obvious advantages.On the other hand,compared with Ti cathode,the potential of nitrite peak of the Ti-Sn O2 cathodes was smaller,while that of the Ti(100-?)Cu? cathodes was greater.But at the same time,the current of nitrite peak of the Ti(100-?)Cu? cathodes was significantly greater.Hence although the adsorption activity on NO2-of the Ti(100-?)Cu? cathodes was weaker than that of the Ti-Sn O2 cathodes,but the reduction activity on NO2-of which was stronger.Consequently,the yield of generated ideal products N2,reduced from nitrite,of these two types of cathodes was almost the same. |
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