Study On The Electronic Structures And Electrochemical Properties Of Ab-Type Hydrogen Storage Alloys

In this paper, the relationship between the electronic structures and the hydrogen storage performance of TiM (M=Fe, Co, Ni), TiFexM1-x(M=Cr, Mn, Ni, Co, Al) and their hydrides are studied by using the SCC-DV-Xa method. By means of pattern recognition, the effect of the content of TixZryNiz alloys on the discharge capacity is investigated. Based on the artificial neural network (ANN) method, the discharge capacity of TixZryNiz alloys and the equilibrium plateau pressure of TixFeyMnz alloys are also predicted. The electrochemical properties of TiFe alloy prepared by high frequency introduction melting and mechanical alloying (MA) have been discussed. The results are shown in the following:1. For the TiM (M=Fe, Co, Ni) hydrides, the bond formed between H and M is weak, the hydrides can absorb/desorb hydrogen reversibly on certain condition. As far as TiFe hydride is concerned, the delocalized chemical bond between Fe and Ti atom is strengthened, which causes a resistance to pulverization during repeated absorbing and desorbing hydrogen.The stability of TiFexM1-x(M=Cr,Mn,Ni,Co,Fe) hydrides decreases with transferred atomic charge increasing in M4s orbital. The bond formed between H and Al is very weak in TiFexAl1-x hydride as comparing to that in TiFexM1-x(M=Cr,Mn,Co,Ni), thus TiFexAl 1-x alloy shows a clear drop of hydrogen storage capacity.2. For TixZryNiz alloys, the influence of Ti content on discharge capacityis opposite to that of Zr content, increasing Ti content and reducing Zr content is beneficial to the discharge capacity.By ANN method, the prediction values of the discharge capacity of TixZryNiz alloys and the equilibrium plateau pressure of TixFeyMnz alloys are in good agreement with experimental results.3. TiFe alloys prepared by high frequency introduction melting are difficult to activate compared with those prepared by MA. The maximum discharge capacity is obtained after 31 cycles (17.15mAh/g) or at the first cycle (34.37mAh/g) for the melting alloys and the ball-milling alloys, respectively.