The Effect Of Surface Modification On The Electrochemical Characteristics Of Lamgni_3.7co_0.3 Hydrogen Storage Alloy

In this thesis, previous research works on AB2 type hydrogen storage alloy of La-Mg-Ni system and development status of the surface modifications of hydrogen storage alloys have been extensively reviewed. On this basis, the LaMgNi3.7Co0.3 hydrogen storage alloy were selected as the subject, then the effect of modification of the additives which added to the electrode and electrolyte, nickel coated and copper coated by surface electroless plating on electrochemical properties of LaMgNi3.7Co0.3 hydrogen storage alloy was studied. The phase structure and electrochemical properties of alloy electrodes was studied by means of XRD, SEM and XPS.First, effects of the different plating on the structure and the electrochemical properties of the LaMgNi3.7Coo.3 hydrogen storage alloys were systemically studied by changing plating condition, which included the ion concentration of Cu2+ or Ni2+ in the plating solution, the pH value and the reaction temperature. Experiment results showed that the optimal conditions of copper-coated was pH 3.0, the concentration of Cu2+ is 1.2g/L, reaction temperature is 30℃and reaction time was 2min; the optimal conditions of nickel-coated is pH 8.0, the concentration of Ni2+ is 40g/L, reaction temperature is 50℃and reaction time is 30min. After surface electroless plating, the maximum discharge capacity and cyclic stability of the alloy electrodes were great improved. The results of linear polarization and impedance spectroscopy show that hydrogen storage alloys coated could increase exchange current density I0, reduce electrochemical reaction resistance, so the electrode kinetics performance was successfully improved.In addition, the effect of modification of the additives on electrochemical properties of LaMgNi3.7Coo.3 AB2-tpye alloy was studied also. the electrochemical properties and cyclic stability of the alloy electrodes were improved greatly after the additives of metal powders and rare earth oxide. The discharge capacity was improved by using La2O3 and V2O5 additive in the electrode, the maximum discharge capacity was increased from 294mAh/g to 351mAh/g and 342mAh/g respectively, Discharge capacity decline rate was reduced from 46.6% to 16.1% and 17.1% respectively. The maximum discharge capacity was increased by 15.9% after the additives of ZnO were added to the electrolyte.Study on the degradation mechanism of LaMgNi3.7Co0.3 alloys shows that serious corrosion of La and Mg is the main reason to the degradation, the corrosion substance forms a inhibitory coated layer at the surface of alloy particles, decreasing the kinetics, lowering the electrochemical properties.