Hydrogen absorption–desorption features and degradation mechanism of ErNi3 compound

• ErNi3 has a better structural stability than other RNi3 compounds during hydriding.
• Two plateaus of PCT curves at 273 K corresponds to ErNi3H∼1.3 and ErNi3H∼4.
• Cycling performance of ErNi3 is far worse than that of LaNi5.

The hydrogen absorption–desorption features and degradation mechanism of ErNi3 compound are investigated in detail. It is fount that two plateaus exist in the P–C isotherms where the lower one corresponds to ErNi3H∼1.3 and the higher one to ErNi3H∼4. Their enthalpy changes are −27.42 and−23.51 kJ/mol H2, respectively, in hydriding process. During hydrogen absorption–desorption cycles, however, ErNi3 shows a bad cycling performance which is attributed to partial decomposition of ErNi3 into ErNi2 and ErNi5 as well as increase of host-lattice strain due to the remained H atoms.