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

Fuel cell is an energy conversion device which can directly converts the chemical energy into electrical energy,and is known as the fourth type of power generation technology after hydropower,thermal power,and nuclear energy.Compared with other energy storage/conversion technologies,fuel cells have technical advantages such as high energy conversion efficiency,environmental friendly,high reliability,and therefore will play an indispensable and important role in the future energy economic architecture.Direct hydrazine fuel cell?DHFC?use high energy density and lower cost hydrazine hydrate?N₂H₄?H₂O?as fuel.Owing to the high theoretical potential,low operating temperature,product environment-friendly and no need the usage of precious metal anode catalyst,DHFC have great potential for invehicle/portable power applications.At present,one of the key problems restricting the commercial application of DHFC is the lack of anode electrocatalysts that can efficiently catalyze the oxidation of hydrazine.The feasible way to solve this problem is to deeply analyze the catalytic mechanism of the electrochemical oxidation reaction of hydrazine,and obtain the correlation between the phase,structure and performance of the hydrazine oxidation catalyst so as to guide the composition,structure design and controlled synthesis of the catalyst.This article takes nickel-based hydrazine oxidation electrocatalyst as the research object,focusing on the design and preparation of high-efficiency and low-cost DHFC anode catalyst,and the relationship between the catalyst phase composition-structure-performance and other issues.The main progress has been made as follows:?1?A 3D hierarchical nanostructured Ni₃N/Ni/NF electrocatalyst was prepared by hydrothermal method combined with nitriding treatment,in which Ni₃N nanoparticles was dispersed on the surface of the Ni nanosheets,while the Ni nanosheets with porous structure were randomly oriented Growing on the surface of nickel foam.First-principles theoretical calculations show that Ni₃N is metallic,and its intrinsic activity of catalyzing the oxidation of hydrazine is superior to that of metal Ni;constructing a hierarchical nanoporous structure helps increase the number of active sites and improve their accessibility.Based on the above reasons,the onset potential of hydrazine oxidation of Ni₃N/Ni/NF catalyst is as low as-0.06 V?vs.RHE?,and the current density at the potential of+0.30 V?vs.RHE?reaches 623 m A?cm^–2.The catalytic activity of the 12-hour constant current test showed no obvious decline,and the comprehensive catalytic performance was at the top level of similar catalysts.?2?The Ni-Co/Ni-Co-O/NF nanocomposite electrocatalyst with a urchin-like nanostructure was prepared by hydrothermal method combined with a reducing hydrogen atmosphere heat treatment method.The hydrazine oxidation activity of the catalyst under alkaline conditions is closely related to the reduction heat treatment temperature.The samples with 300?C reduction heat treatment exihibits the best catalytic activity,and lowering or increasing the temperature leads to different degrees of activity reduction.The phase/microstructure/chemical state analysis shows that the change in the activity of Ni-Co/Ni-Co-O/NF catalyst may be due to the change of the number of active sites and the conductivity.The above research work has designed and synthesized two supported nickel-based hydrazine oxidation electrocatalysts by combining various modification strategies and simple preparation methods.While improving the performance of DHFC anode catalysts,it enriched/deepened the phase composition-structure-performance correlation of nickel-based hydrazine oxidation catalysts,and provided experimental and theoretical basis for the development of efficient and low-cost DHFC anode catalysts.