Effect of Co substitution on hydrogenation behavior of GdNi3-xCox (x = 0, 0.2, 1.0) and crystal structure of its hydride phases

Abstract The effect of substituting Co for Ni in GdNi3 on the hydrogenation properties and phase transformation during the hydrogen absorption–desorption process of GdNi3-xCox (x = 0, 0.2, 1.0) was investigated using P–C isotherms and X-ray diffraction analysis (XRD). GdNi3 showed a residual hydrogen content of 0.6 H/M after the first desorption process. The maximum hydrogen capacity of GdNi3 was 1.0 H/M, while the reversible hydrogen capacity decreased to 0.4 H/M because of the residual hydrogen. The reversible hydrogen capacity was improved to 1.0 H/M in GdNi2.0Co1.0, and two plateaus were observed in the absorption–desorption process. The crystal structures of the full hydride phases GdNi3H3.8 and GdNi2.8Co0.2H3.8 could not be determined because of the heavy peak broadening in the XRD pattern, while the PuNi3-type structure of the original alloy was retained in the full hydride phase GdNi2.0Co1.0H3.6. The retention rates of GdNi3 and GdNi2.0Co1.0 at 100 cycles were 75% and 92%, respectively. The cyclic properties of GdNi2.0Co1.0, up to 100 cycles, favorably compared with those of LaNi5, which was found to be related to the small lattice strain formed during the first hydrogen absorption process.