Crystal and electronic structure manipulation of Laves intermetallics for boosting hydrogen evolution reaction.

Since the 1970s, Laves intermetallics (AB) have been widely used in hydrogen storage technology (e.g., nickel-metal hydride batteries) due to the abundant interstitial sites and moderate metal-hydrogen bond strength (E). They, however, have been rarely used in the hydrogen evolution reaction (HER) because of the same reason (i.e. moderate E), which results in poor HER efficiency. In this study, by applying lanthanide contraction and ligand effect, we have successfully lowered the E and substantially boosted the HER activity of Laves intermetallics (RECo and RERuCo (RE = Pr, Tb, Y and Er)) to outperform those of commercial Pt/C catalyst. Hydrogen overpotential decreases from ErCo (η = 169 mV) to PrCo (η = 113 mV) and then to PrRuCo (η = 29 mV). The expansion of lattice constants for PrCo may alleviate the obstacle of H atom diffusing through interstitial sites, while the inclusion of Ru element can raise the antibonding population of Co-Co/Ru bonds, which consequently lowers E and thus elevates HER activity according to the Sabatier principle. This outcome indicates that the manipulation of the crystal structure and electronic structure factor is an efficient strategy to boost the HER activity of Laves intermetallics.