The Fuel Cell Anode Performance And Biodegradable Behaviors Of Three Magnesium Alloys

As the anode material of magnesium fuel cell,magnesium has the advantages of high energy density,low cost and stable discharge voltage,magnesium has good application prospects in the field of marine energy development.At the same time,magnesium is also known as "green material in the 21 st century".It has good biocompatibility and biodegradability,magnesium has a good application prospect in the field of orthopedics and cardiovascular implants.In order to solve the problem of hydrogen evolution and uncontrollable degradation rate of magnesium in long-term use,three different magnesium alloy materials（AZ31,AZ91 and LZ91）were prepared by adding lithium,aluminum,zinc and other metal elements to pure magnesium.The fuel cell anode performance and biodegradable behaviors as implantable materials of these three magnesium alloys were investigated.First,the electrochemical performance of pure magnesium and three magnesium alloys in 3.5% Na Cl solution were investigated by electrochemical methods（Open circuit potential,Tafel polarization curve method,Linear voltammetry method,Electrochemical impedance spectroscopy,Constant potential current time method）.The effects of adding different elements and different proportions of adding elements on the electrochemical performance of magnesium alloy anode materials were investigated.The result showed that the order of electrochemical activity of the four metals from large to small was LZ91>Mg>AZ91>AZ31,and the order of corrosion resistance from large to small was AZ31>AZ91>Mg>LZ91.At the constant potential,the order of discharge current density from large to small was LZ91>AZ31>AZ91>Mg.It was shown that the adding of Li element improved the electrochemical activity of magnesium,reduced corrosion resistance and increased discharge current density.Adding Al element reduced the electrochemical activity of magnesium,improved corrosion resistance,and made the discharge current more stable.With the Al content in the Mg-Al alloy decreasing,the electrochemical activity decreased,the corrosion resistance increased,and the discharge current density increased.The morphology and surface products of the magnesium alloys after discharging were characterized by scanning electron microscopy,energy spectrum and X-ray diffraction.The result showed that the discharge products of LZ and AZ magnesium alloys were less than pure magnesium’s,the surface of LZ91 had deeper cracks,and the surface of AZ91 and AZ31 had smaller cracks.The discharge products of magnesium and AZ magnesium were composed of Mg（OH）₂,and the LZ91 discharge products were composed of Mg（OH）₂ and Li₂O₂.Secondly,the effects of long-term hydrogen evolution on the electrochemical behavior of four metals were investigated by long-term Tafel polarization curve experiments,electrochemical impedance spectroscopy experiments,hydrogen evolution experiments and weight loss experiments.The result showed that with the increasing of the immersing time,the activation potential of LZ91 gradually changed negatively and the corrosion resistance decreased,the activation potential of AZ91 gradually changed positively and the corrosion resistance increased.The activation potential of AZ31 at each moment was positive than AZ91’s,and the corrosion resistance of AZ31 was stronger than AZ91.The order of hydrogen evolution rate from large to small was Mg>LZ91>AZ91>AZ31.It was shown that adding Li element and Al element reduced the hydrogen evolution rate,and the addition of Al element was better than the addition of Li element.Finally,the long-term degradation rate of pure magnesium,AZ91 and LZ91 magnesium alloy in Hank’s simulated body fluid was investigated by hydrogen evolution experiment,weight loss experiment and solution p H experiment.Degradation performance of magnesium alloy in Hank’s simulated body fluid was investigated by electrochemical method（Tafel polarization curve method,Electrochemical impedance spectroscopy）.The surface of the degraded magnesium alloy was characterized by scanning electron microscopy,energy spectroscopy and X-ray diffraction.The result showed that the order of the hydrogen evolution rate and weight loss rate of the three metals from large to small was Mg>LZ91>AZ91.After 48 hours degradation,the order of the solution p H from large to small was Mg（8.5）>LZ91（8.29）>AZ91（8.1）.It was shown that the degradation rate of pure magnesium in Hank’s simulated body fluid was the largest.Adding Li element and Al element reduced the degradation rate of magnesium alloy in Hank’s simulated body fluid.The effect of inhibiting degradation of magnesium alloy by adding Al element was better than the adding Li element.The order of activation potential from negative to positive was LZ91>Mg>AZ91.With the increase of time,the activation potential of LZ91 slowly changed positively,and the activation current decreased slowly.The activation potential of AZ91 slowly changed negatively,and the activation current remained basically unchanged.The order of impedance from large to small was AZ91>LZ91>Mg.With the increase of time,the impedance of the three alloys increased.Scanning electron microscopy after degrading showed that the surface of pure magnesium had more cracks and white degradation products.The surface of AZ91 had fewer cracks,and some of the surface remained smooth and intact.The surface of LZ91 had obvious cracks.The magnesium and AZ91 degradation products were composed of Mg（OH）2 and the LZ91 degradation products were composed of Mg（OH）₂,Li₂O₂ and LiOH.