Effect Of Elemental Substitution And Graphe-based Complexes On The Electrochemical Properties Of?La,Mg?Ni_2.8Co_0.7 Metal Hydride Alloys

In this paper,La_1-xMg_xNi_2.7Co_0.8?x=0.15,0.2,0.25,0.3at%?hydrogen storage alloys were prepared by magnetic levitation melting under argon atmosphere.,NiCo@rGO,Ti02/N-rG0 nanocomposites were prepared by the thermal method.The effects of magnesium partial substitution of lanthanum,graphene-loaded bimetallic elements?nickel and cobalt?and graphene-loaded titanium oxide/nitrogen on the electrochemical hydrogen storage properties of La-Mg-Ni-based alloys were investigated.The results show that when the substitution amount of Mg to La is r=0.25,the discharge capacity of La1-xMgxNi2.7Co0.8?x=0.25at%?alloy electrode reaches the maximum value,and the discharge capacity is 380 mAh·g-1.In addition,x=0.25 corresponds to the alloy electrode showing good kinetic performance.For example,when the discharge current density is 1500 mA/g,the high-rate discharge performance HRD,500 of the La1-xMgxNi2.7Co0.8?x=0.25at%?alloy electrode is 50.5%,and the HRD1500 of the remaining magnesium-containing hydrogen storage alloy electrode is smaller than 32%.At the same time,the anodizing peak current density Ip,the exchange current density Ie of the alloy electrode and the hydrogen diffusion coefficient D in the alloy electrode reach a maximum value.Obviously,the alloy electrode corresponding to x=0.25 has the best electrochemical performance.Based on La_0.75Mg_0.25Ni_2.8Co_0.7,it showed good electrochemical performance.It was found that the modified graphene oxide-supported titanium oxide/nitrogen?TiO2/N-rG0?composite was used as a catalyst to modify it.When Ti02/N-rG0 with a mass fraction of 5 wt%was added to the alloy electrode,the maximum discharge capacity of the alloy electrode increased from 380 mAh·g-1 before addition to 414 mAh·g-1,and the high-rate discharge performance HRD1500 of the alloy electrode increased from 50.2%to 71%.The exchange current density of the La_0.75Mg_0.25Ni_2.8Co_0.7-TiO2/N-rGO alloy electrode is 211.1 mA/g,and the exchange current density of the electrode with no catalyst added and rgo,N/rgo,Ti02/rgo catalyst is added.They were 110.8 mA/g,135.4 mA/g,120.6 mA/g,and 115.7 mA/g,respectively.After the addition of TiO2/N-rG0 nanocomposites,the diffusion ability of hydrogen atoms in the alloy electrode and the exchange current density of the alloy electrode surface are better than that of rGO,N/rGO,Ti02/rG0 under the synergistic effect of Ti02 and N.When the NiCo@rGO composite is used as a catalyst for La-Mg-Ni based alloy electrodes,it had better catalytic activity than rGO,Ni/rGO and Co/rGO.The peak current density of the NiCo@rGO catalyzed electrode reached 2137 mA/g,while that of Ni/rGO,Co/rGO and rGO was only 1220 mA/g,1257mA/g and 1753mA/g respectively.In addition,the limiting current density IL of the alloy electrode was increased from 1450 mA/g to 2378.5 mA/g with added NiCo@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 4.89×10-10 cm2/s to 6.38×10-10 cm2/s,and the HRD values at a discharge current density of 1500 mA/g?HRD1500?reached 73.5%with the addition of 5wt.%NiCo@rGO.