Effect Of Graphene-based Complexes On The Electrochemical Properties Of La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5

In this dissertation,La0.7Mg0.3(Ni0.9Co0.1)3.5 hydrogen storage alloys were prepared by magnetic levitation melting under argon atmosphere.Cr2O3@rGO,Pd@rGO,Ni/N-r-GO nanocomposites were prepared by the thermal method.The graphene-based nanocomposites were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),and energy dispersive spectroscopy(EDS).The results show that the composite of Cr2O3 based on graphene,Pd distributed on graphene,and nitrogen-doped graphene supported Ni were synthesized successfully.Finally,the composites as catalysts were mixed with hydrogen storage alloy powder in different ratio and then prepared rounded electrodes,and electrochemical performance of alloy electrodes were performed by Hantaisite and Gamry.The results show that the electrochemical performance of the alloy electrode fabricated by added Cr2O3@rGO,Pd@rGO,Ni/N-rGO has been significantly improved.When the 4.5 wt.%Cr2O3@rGO composite catalyst was added,the peak current density and limiting current density of the alloy electrode were improved.The charge transfer resistance Rct of alloy electrodes prepared by added 2.5wt.%and 4.5 wt.%Cr2O3@rGO composite respectively was obviously lower than the alloy electrode without catalyst added.The hydrogen diffusion coefficient of the alloy electrode without catalyst was 4.45 ×10-10 cm2/s.After added the catalyst,the hydrogen diffusion coefficient was improved,such as,the alloy electrode with the addition of 4.5wt.%Cr2O3@rGO reached 5.54×10cm2/s.These show that the alloy electrode with the addition of 4.5wt.%Cr2O3@rGO composite has the best kinetic performance,and the HRD values at a discharge current density of 1500 mA/g(HRD 1500)reached 73.2%.When Pd@rGO was applied as a catalyst for the hydrogen storage alloy electrode,the peak current density of the electrode with the addition of 2 wt.%Pd@rGO reached 1779.2 mA/g.The anode peak current densities of the alloy electrode with the addition of 2 wt.%rGO,1wt.%Pd@rGO and 3 wt.%Pd@rGO were 892.6 mA/g,1250.3 mA/g and 1670.4 mA/g,respectively.In addition,the limiting current density IL of the alloy electrode with 2 wt.%Pd@rGO was 1968.3 mA/g,and with the addition of 2 wt.%Pd@rGO,the hydrogen diffusion coefficient of hydrogen in the alloy was increased from 1.32×1 0-10 cm2/s to 1.63×10-10 cm2/s.The high rate discharge performance of the alloy electrode has been significantly improved after the addition of the catalyst such as GO and Pd@rGO.For example,the alloy electrode HRD 1500 of the AB3.5 alloy electrodes increased from 0 to 67.1%,54%,73.5%,and 56.6%with the addition of 2 wt.%rGO,1 wt.%Pd@rGO,2 wt.%Pd@rGO and 3 wt.%Pd@rGO,respectively.Ni/N-rGO catalyzed hydrogen storage alloy electrode,it had better catalytic activity than rGO,N-rGO and Ni/rGO.The peak current density of the Ni/N-rGO catalyzed electrode reached 2309.8 mA/g,while that of Ni/rGO,N-rGO and rGO was only 1032.2 mA/g,1405.4 mA/g and 1415.2 mA/g,respectively.In addition,the limiting current density IL of the alloy electrode was increased from 1485.7 mA/g to 2746.6 mA/g with added Ni/N-rGO.The charge transfer resistance was also significantly reduced relative to other catalysts,and the diffusion coefficient D of hydrogen in the alloy was increased from 3.93×10-10 cm2/s to 6.15×10-10 cm2/s,and the HRD values at a discharge current density of 1500 mA/g(HRD1500)reached 70.5%with the addition of 5 wt.%Ni/N-rGO.