Ternary LaNi4.75M0.25 hydrogen storage alloys: Surface segregation, hydrogen sorption and thermodynamic stability

Abstract Modification of compounds like LaNi 5 toward ternary compositions change alloy hydrogen storage properties and influence resistance to hydrogen contamination. Below thermodynamic properties of ternary alloys LaNi 4.75 M 0.25 are investigated with ab initio methods and synthesized in order to select the composition with hydrogen sorption properties not worse than LaNi 5 . The specific volume change, surface segregation energy and change of the hydride formation enthalpy are calculated for 34 elements (M: Ag, Al, Au, B, Bi, Ca, Cd, Cu, Cr, Fe, Ga, Ge, In, Ir, K, Mg, Mn, Mo, Nb, Pb, Pd, Pt, Rh, Ru, Sb, Sn, Ti, V, W, Y, Zn, Zr) substituting Ni. Five ternary compounds are synthesized and analyzed with respect to crystal structure and hydrogen sorption properties. Compounds like LaNi 4.75 Ag 0.25 . and LaNi 4.75 Pb 0.25 show favorable stability and H 2 sorption thermodynamics. The substituting elements segregating toward the surface are expected to be catalytically active for hydrogen contamination gasses.