Study Of Synthesis And Catalytic Properties Of Nickel-Based Anode Electrocatalysts For Direct Hydrazine Fuel Cell

Direct hydrazine fuel cell(DHFC),which uses hydrazine(N2H4)as a fuel,has attracted considerable attention owing to its many advantages.First,the reulting nitrogen and water from N2H4 electrooxidation is environmental friendly.Second,DHFC yields a theoretical cell voltage of+1.56 V and high theoretical energy density(5.42 Wh·g-1).Last,DHFC can be operated at near-ambient temperature.However,the sluggish kinetics of N2H4 electrooxidation is critical to DHFC.As a result,seeking anode catalysts with superb electrocatalytic performance is paramount to the development of DHFC applications.In this paper,cost-effective supported Ni-based catalysts with extraordinary electrocatalytic performance were synthesized,using X-ray diffraction(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM)and X-ray photoelectron spectroscopy(XPS)to characterize the phase structure and surface morphology,and measuring various electrocatalytic performances using linear sweep voltammetry,cyclic voltammetry,electrochemical impedance spectroscopy and chronoampermetry methods,and did some research on the relationship between the structure and electrocatalytic performance,the research results lay foundation to the development of DHFC.This paper includes the following chapters:1.One-step synthesis of NixP electrocatalyst using nickel foam(NF)as substrate and NaH2PO2 as P source.XRD revealed the formation of two Ni phosphides Ni12P5 and Ni2P.SEM results showed that poorly defined shapes of nanorods with lengths ranging from 200 to 400 nm were vertically aligned on the NF substrate.Thus-synthesized electrocatalyst exhibited exceptionally high activity and excellent durability.For example,at+0.30 V vs.reversible hydrogen electrode,the current density reached up to 580 mA·cm-2,which is among the top level of the electrocatalysts reported up to date.By experimental characterizations and theoretical calculations,we gain insight into the high electrocatalytic activity should stem from:(1)electrochemical impedance spectroscopy suggested the good electric conductivity;(2)the nanorod morphology ensured the exposing of more active sites;(3)first-principles calculations revealed that Ni2P exhibited higher intrinsic activity than metallic Ni.2.The nickel molybdenum oxide was synthesized using a hydrothermal method with the NF as substrate,following the annealing treatment under H2 atmosphere to achieve the hierarchically nanostructured electrocatalyst.Thus-prepared catalyst exhibited exceptionally high activity towards N2H4 electrooxidation,but meanwhile showed high activity towards non-faradaic N2H4 decomposition.The problematic decomposition decreases the fuel efficiency and somehow enfluence the voltage.In an effort to alleviate this problem,together with the understanding of the electrocatalysts from last work,we conducted controlled surface phosphorization process.By adjusting the amount of NaH2PO2 and the annealing temperature,the non-faradaic decomposition reaction was effectively suppressed without decreasing the electrocatalytic activity.