Study On Preparation And Properties Of Nickel–based Anode Catalyst For Direct Hydrazine Fuel Cell

In recent years,the direct hydrazine fuel cell?DHFC?gradually get the attention of people mainly because of the following advantages:high theoretical electromotive force of+1.56 V,high energy density(5.42 Wh·g^-1),pollution–free electrochemical reaction product?N₂ and H₂O?,moderate operation temperatures?40–80 ^oC?and could use the infrastructure of existing gas stations to store and transport fuel.In contrast to other fuel cells,the most prominent feature of DHFC is the use of cheap non–precious metals as electric catalysts.The performance of DHFC mainly depends on the electrode catalyst,especially the anode catalyst.After several decades of development,the study found that the performance of Ni base binary and three–element anode catalyst is much better than that of other single metal catalysts.Although the development of these anode catalysts has made remarkable progress,there is still considerable room for improvement.In this paper,the preparation and electrocatalytic properties of DHFC anode catalysts were studied,and Ni–Zn and Pd–Ni binary anode catalysts were prepared.The structure and properties of the catalysts were studied.The catalyst has demonstrated excellent catalytic performance and operational stability for hydrazine electrooxidation reaction,and the results of the study have laid the experimental and theoretical foundation for the practical application of DHFC.The main contents of this thesis are as follows:?1?A nickel foam–supported Ni–Zn alloy catalyst is synthesized by the electrodeposition and anodic dissolution methods.The developed catalyst with an open nanowall network structure and robust adhesion exhibits high activity and good durability for electrooxidation of hydrazine in alkaline medium.For example,a current density of 300 mA·cm^-2 at 0.40 V and an onset potential of-0.15 V vs.reversible hydrogen electrode?RHE?are achieved in a 0.10 M hydrazine and 1.0 M NaOH solution at 30°C.XRD,SEM and XPS were used to study the composition,surface morphology and the valence state of the constituent elements,and the reasons for the excellent electrochemical properties of the catalyst were analyzed.Its performance increase can be attributed to two points:?1?chemical etching Zn,which causes the catalyst to have the three–dimension layer structure of the open hole,increase the electrochemical specific surface area of the catalyst and the number of catalyst active sites;?2?Zn in the Ni–Zn alloy catalyst changed the electronic structure of the active phase Ni,which enhanced the intrinsic activity of the catalyst.?2?A Pd–modified porous Ni electrocatalyst with nanotube–like structure was successfully prepared using a combination of the dealloying and galvanic replacement methods.The resultant Pd–Ni/Ni foam showed extremely catalytic activity and excellent cycling stability towards the hydrazine electrooxidation.For example,a current density of 760 mA·cm^-2 at0.60V vs.RHE can be achieved in 0.10 M N₂H₄·H₂O and 1.0 M NaOH solution at 30°C.The developed electrode with the enhanced electrocatalytic property should be primarily attributed to its porous structure and incorporation of Pd element,hence enhancing the number of active sites and intrinsic activity of each site.This result provides a good guideline for design and synthesis of the high–performance electrocatalyst.