Design,Synthesis And Study Of Catalytic Properties Of Nickel-based Anode Electrocatalysts For Direct Hydrazine Fuel Cell

Fuel cell is a clean and efficient energy conversion technology,which is expected to play an important role in the future clean energy system.Among various types of FCs,the direct hydrazine fuel cell（DHFC）stands out and has attracted extensive attention due to its advantages such as high energy density,strong environment affinity and use of cheap metal catalysts.Searching for high-performance and low-cost anode catalysts for N₂H₄ electrooxidation is a core task in the DHFC research,which requires a judicious selection of intrinsically highly active materials and smart structure engineering of electrodes to maximize active site density and to construct electronically conductive network.Over the past decades,a series of non-noble alloy or compound which can efficiently catalyze electrochemical oxidation of hydrazine have been developed by using of a variety of material modification strategies.However,in general,the electrocatalytic activity and durability of existing catalysts still fall far short of the requirements for commercial application.The reason is that the experimental and inefficient exploration mode formed due to the lack of rational design under the guidance of mechanism understanding has seriously delayed the catalyst research and development process.Based on that current research status,this thesis aims to develop DHFC anode electrocatalysts with high activity and good stability,and selects the transition metal phosphides（Ni₂P）and nitrides（Ni₃N）as main research objects,focusing on the design and preparation of catalysts and the correlation between phase composition-microstructure-electrocatalytic performance of catalysts.The research progress are as follows:（1）The NF-supported Ni@Ni₂P core-shell nanotube arrays catalyst（Ni@Ni₂P NTA/NF）is fabricated by combined using electrodeposition,sacrificial template method followed by phosphatization treatment.The Ni₂P shell exhibits high intrinsic activity towards hydrazine electrooxidation and possesses good conductivity.Meanwhile,the constructed porous hierarchically nanotube arrays structure efficiently increases the number of active sites and improves the reactant accessibility.On the basis of above reasons,the Ni@Ni₂P NTA/NF catalyst prepared under the optimized conditions exhibited exceptionally high activity,good stability and nearly 100%selectivity for the complete N₂H₄ electrooxidation following the four-electron pathway,outperforming existing anode electrocatalysts of DHFC.（2）The NF-supported Ni@Ni₃N core-shell nanotube arrays catalyst（Ni@Ni₃N NTA/NF）is fabricated by combined using electrodeposition,sacrificial template method followed by nitriding treatment.It is found that the nitriding time is an important factor influencing phase structure and catalytic performance of the target catalyst.The catalyst prepared when the nitriding time is 1.5 h shows the best performance,and its onset potential is at-0.07 V vs.RHE,the current density obtained at potential of 0.3 V vs.RHE reaches 1011 m A×cm^-2,which is higher than most reported DHFC anode electrocatalysts.The reason for the excellent catalytic performance of Ni@Ni₃N NTA/NF catalyst should be attributed to the combination of high intrinsic activity,abundant active sites and good conductivity.The above research works follow the electrocatalyst design concept of simultaneous optimization of intrinsic activity,the number of active sites and the conductivity,design and synthesize two types of core-shell nanotube arrays catalysts.In addition to enhancing the catalytic performance of DHFC anode catalysts,it has deepened the understanding of the correlation between phase composition-microstructure-electrocatalytic performance of catalysts,which has important reference value for the development of high-performance and low-cost DHFC anode electrocatalysts.