An Investigation On The Eelectrochemical Performance And Gaseous Hydrogen Storage Performance Of RE-Mg Based LaMgNi₄-type Hydrogen Storage Alloy

With the development of social economy, environment problem is becoming more serious.Many parts of the country are influenced by haze which is harm profoundly to people’s healthsince the winter of2012. The main source of leading to haze phenomena is cars, which emit alarge amount of waste gases into the air. Although the growth in auto market of China droppingslightly but, analysts think, there still is a hunger for cars. To solve the above-mentionedproblem, accelerating the development of new energy vehicles which are expected to substitutetraditional vehicles has become a popular topic. National has implemented numerous policies tobooste the development of new energy vehicles market. Now, Nickel-metal-hydride batteries（Ni/MH） are widely used for different brands and models of new energy vehicles. However, thecore components of Ni/MH batteries, AB5-type hydrogen storage alloys are obviously difficultto meet the market demand due to the limite of lower capacity. The theoretical capacity ofAB2-type LaMgNi₄hydrogen storage alloys can reach to480mAh/g, is1.3-1.4times as muchas LaNi₅-type alloy in the discharge capacity, which raised comprehensive attentions around theworld.The article employs induction melting method to prepare RE-Mg based AB2-typeLaMgNi₄hydrogen storage alloys. To curb the volatilization of Mg and RE,0.04MPa helium isfilled in the vacuum intermediate frequency induction furnace. Besides, we added extra10%Mg and5%RE to make up for the volatilization and melting loss inthe process of melting. Theelectrochemical characters of alloy electrodes are tested on LAND analog programmablebattery tester, including discharge capacity, cycle stability and high rate discharge performance,etc. The charge transfer resistance Rct, exchange current density I0, limiting current densityILand hydrogen diffusion coefficient D are obtained by the results which are tested onPARSTAT2273type electrochemical workstation.Through studies of the electrochemical character of alloys, it was revealed that all of themhave excellent activation properties and can achieve the maximum discharge capacity in one or two charge-discharge cycles, however, the maximum discharge capacity drops in differentdegree after substituting La with Ce, Pr, Nd, Sm. The maximum discharge capacity achieves to313.7mAh/g of the basis alloy. That compares to81.4,274.5,269.9,233.8mAh/g for Ce_0.4,Pr_0.4, Nd_0.4, Sm_0.4alloys, respectively. The cycle stability is improved to different degrees. Forexample, the cycle time n is41when the discharge capacity drops to less than60%of themaximum diacharge capacity, however, the n values increase to668,125,287,236for Ce_0.4,Pr_0.4, Nd_0.4, Sm_0.4alloys. The effect of element substitution on high rate discharge performanceis complex, which is relations with the the charge transfer resistance between the surface ofthe electrode and electrolyte interface and the diffusion of hydrogen atomic in the alloys.The hydrogen storage capacity and hydriding rates of these alloys should be different fordifferent substitutable elements. For instance, the hydrogen storage capacity drops with theincrease of Ce content and the hydriding rate is the opposite. The hydrogen storage capacityincreased at first but decreased finally which achieves the maximum vaule at Sm0.3alloy. Themicrostructure and the hydrogen storage capacity of containing Pr alloys are investigated, theresults show that elements substitute is helpful to suppress the hydrogen inducing amorphizationtend.