Preparation Of Phosphatized Alloy/core-shell Structure Catalyst And Electrocatalytic Hydrazine Oxidation

Direct hydrazine fuel cell?DHFC?is one of the future clean energy technologies,which has been widely concerned by people due to the advantages of high specific energy,convenient use and low pollution.Catalyst is an important part of direct hydrazine fuel cell and plays a crucial role in performance,however,its development is limited by high prices.Therefore,it is urgent to develop low-cost catalysts with high catalytic performance.Nonmetallic phosphorus not only has abundant valence electron structure,but also can affect the electronic state of metallic elements.In recent years,adding nonmetallic phosphorus into metal catalysts not only reduces the cost of catalysts,but also exert good synergistic effect between phosphorus and metals,greatly improving the catalytic performance.Accordingly,the corresponding investigations of non-metallic phosphorus have become focus of researchers.Therefore,a phosphatized alloy and core-shell catalyst was developed and its application in hydrazine oxidation system was studied.The purpose of this thesis is to prepare low cost and high activity hydrazine fuel cell anodic catalyst.As the starting point:reducing the cost of the catalyst with the advantages of nonmetallic phosphorus.To develop a phosphatized alloy/core-shell structure catalyst suitable for hydrazine electrocatalytic oxidation as the final purpose.Firstly,we prepared phosphatized CuNi alloy nanoparticles and used for investigating hydrazine electrocatalytic oxidation.Subsequently,the prepared phosphatized Fe@Cu/C electrocatalyst was used for hydrazine oxidation.Finally,a phosphatized core-shell Ni@Pt/C loaded carbon electrocatalyst was studied on hydrazine electrocatalytic oxidation.The phosphatized alloy and non-noble/low metal core-shell were successfully extended to the study of catalytic oxidation of hydrazine.In these three parts,physical characterization were used to characterize the structure of the prepared catalysts.Meanwhile,electrochemical measurements were used for investigating their electrochemical properties.The specific research contents are as follows:Part I:The preparation of phosphatized carbon loaded CuNi nanoparticles and study on hydrazine electrocatalytic oxidationCombining the advantages of alloy and non-metallic phosphorus,nanoparticles of CuNi alloy with different carbon loading ratios(n_Cu:n_Ni=1:1,1:2,2:1)were prepared by polyol reduction method,and then the prepared CuNi alloy catalyst was calcined with NaH₂PO₂ at1100 ^oC.The electrocatalytic oxidation of hydrazine in alkaline medium was investigated.The results showed that P-Cu₂Ni/C has excellent electrochemical performance in electrocatalytic hydrazine oxidation under the same conditions.Compared with P-CuNi₂/C,P-CuNi/C,Cu/C,Ni/C,Cu₂Ni/C,P-Cu₂Ni/C has higher oxidation peak current(0.111 A mg^-1_CuNi)and good stability?80.2%?.Thermodynamic studies show that the P-Cu₂Ni/C catalyst has a low Tafel slope and a low activation energy at a high electric potential,which means that the hydrazine oxidation process of P-Cu₂Ni/C at a high potential consumes less energy and is more conducive to the reaction.This excellent performance is due to the synergistic effect between Cu,Ni and P.In addition,the presence of Cu,Ni and P has been demonstrated by XPS spectrum and EDX analysis.In this chapter,the study of phosphatized CuNi nanoparticles has considerable reference value in improving the electrochemical properties of single and bimetallic catalysts.Part II:The preparation of phosphatized core-shell Fe@Cu/C carbon loaded electrocatalyst and study on hydrazine electrocatalytic oxidationFe@Cu/C electrocatalyst was prepared by combining replacement with polyol reduction,finally,electrocatalyst was obtained by phosphatization and successfully applied to hydrazine electrocatalytic oxidation.By regulating the temperature of phosphatization,it was found that the core-shell catalyst had superior hydrazine oxidation catalytic activity(45 mA·mg^-1_FeCu)and long-term stability?93.5%?when the phosphatized process at 300 ^oC,compared with other catalysts.In addition,different scan speed test found that Fe@Cu-P/C on the hydrazine oxidation is an irreversible diffusion control process.The satisfactory results are attributed to Fe@Cu-P/C electric special performance as well as the join of nonmetal phosphorus,that makes good synergistic effect between phosphatized metal shell and metal core at the same time.Through XPS,HADDF-STEM and EDS test,it shows the prepared core-shell electrocatalyst contains Cu?Fe and P elements.To sum up,the phosphatized core-shell Fe@Cu-P/C electrocatalysts laid a good foundation for the development of better catalysts in the future.Part III:The preparation of phosphatized Ni@Pt/C carbon loaded electrocatalyst and study on hydrazine electrocatalytic oxidationOn the basis of phosphatized non-noble metal core-shell catalyst,the Ni@Pt/C catalyst was developed for the electrocatalytic oxidation of hydrazine.Using the same method as the experiment in the second part,the phosphatized temperature?300 ^oC,400 ^oC and 500 ^oC?was further regulated.It was found that the electrocatalyst Ni@Pt-P/C-400 showed better catalytic performance and better stability compared with Pt/C,when the phosphating temperature was400 ^oC.Thermodynamic study showed that the Ni@Pt-P/C-400(12.60 KJ mol^-1)catalyst had lower activation energy than Pt/C(13.42 KJ mol^-1).The reasons for the significant electrochemical performance of the Ni@Pt-P/C-400 catalyst are as follows:on the one hand,the internal electronic effect of nickel leads to the exposure of more active sites in the electrocatalyst;on the other hand,the increase of the d orbital vacancy of Pt in the Ni@Pt-P/C-400 further improves the catalytic performance of the catalyst.The preparation of Ni@Pt/C-P core-shell electrocatalyst not only reduced the amount of precious metal,but also greatly improved the utilization rate of the metal,it provides the feasibility for the application of low-content precious metal catalyst in hydrazine fuel cells in the future.