Lanthanide contraction regulates the HER activity of iron triad intermetallics in alkaline media.

In this work, we have systematically investigated the HER activity of the RECo (RE = Y, Pr, Gd, Tb, Ho and Er) series and revealed that their HER activities are highly correlated with the averaged Co-Co bond length of each compound. The HER performance follows the order of GdCo > TbCo > PrCo > YCo > HoCo > ErCo. This suggests that the unique feature of rare-earth metals, lanthanide contraction, can effectively alter the interatomic spacing and impact the corresponding HER activity. Additionally, GdFe and GdNi with different d electron density in the system were synthesized and comparison of their HER efficiencies is also discussed. GdNi demonstrates the highest HER efficiency among all samples, and it only requires an overpotential (η) of 44 mV to acquire a current density of 10 mA cm. The theoretical calculation offers a clue that the H adsorption energy (GH) for H atoms on Ni is lower than that on Co and Fe due to the high electron population in the antibonding state of the Ni atom. This well explains the origin of the synergistic effect for the high electrocatalytic HER of these iron triad intermetallics.