The Study On Electrochemical Performances Of Magnesium Batteries Electrode Materials

Metal fuel cell (MFC) uses active metals such as zinc, aluminum and magnesium as naegtive electrode instead of hydrogen in H/O fuel cell. MFC is greatly concerned because of its low price, nontoxicity, steady discharge potential plateau, high energy density, plenty of resources, reproducible, etc. Currently, zinc and aluminum is leading in MFC, but magnesium and other metals get little attention.On the other hand, electrolytic manganese dioxide (EMD) has got wide use in primary battery as cathodic material, studying and improving the rechargeability of EMD accords with the request of building environment-friendly society.In this paper, we investigate first the electrochemical properties of AZ31 and AZ61 alloys by means of weight loss, linear sweep voltammetry, chronopotentiometry, Tafel Plot, A.C. impedance. The corrosion inhibiting ability of sodium dodecyl benzene sulfonate (SDBS) and hexamethylenetetramine (HMTA) as additives are also studied. Results indicate that magnesium alloys are inert and difficult to discharge in KOH solution, so KOH solution isn't adopted as electrolyte of magnesium batteries, but in neutral MgSO4 solution, magnesium alloys have small corrosion rates and better active performances. On the basis of LSV, the electrochemical performance of AZ31 in MgSO4 solution is better than AZ61's, by contraries, the results of CP indicate AZ61 is more excellent than AZ31 including discharge current efficiency, electrode potential, potential lag, etc. The phenomena can be explained by difference of Al content in two alloys and the Al participating in the electrochemical discharge reaction. While discharging, there is severe negative difference effect (NDE) which reduces discharge current efficiency. Increasing ebullition of H2 and dropping of granules are intuitionistic causes of NDE. In studied range of concentration, two additives have same"anti-S"shape rule to the inhibiting of AZ31, but in the same range, there are both no effect on AZ61. There is closing relation between inhibiting ability and concentration of additive, surface micrograph of alloys.The rechargeability of EMD in MgSO4 solution is also studied by cyclic voltammetry, chronopotentiometry, XRD and microelectrode technology in this paper. The results have shown that the process of charge/discharge of EMD is the process of insertion/extraction of H+, and the diffusion of H+ in electrode is rate-determining-step. After first cycle of discharge, the capacity of subsequent charge/discharge drops largely, but the capacity can keep stable. XRD patterns reveal that the discharge product of EMD includes two kind of material, one has electrochemical activity, and the other is inert and related to the dropping of capacity. CVs of EMD by microelectrode indicate the same rule about capacity dropping as CP, and there is new reversible material appeared, which is consistent to XRD patterns. Microelectrode technology can well reveal electrochemical properties of EMD.