Anomalous Alloying Effect on Water–Rare-Earth Chemical Bonding

Abstract Conventional single-atom alloying (SAA) effect is generally regarded as a design strategy modulating the surface properties of an alloy system between those of its individual elemental components. For a long time, chemists have used this rule to make single-atom alloys (SAA) with desired catalytic performance. In this study, we have discovered an anomalous SAA effect on water–rare-earth chemical bonding, which is exemplified in the inert Cd(0001) surface doped with single rare-earth atoms (Sc, Y, and La). In contrast to the conventional expectation that the water–rare-earth coupling strength would fall between that of the pure rare-earth surfaces and that of the inert Cd(0001) surface, we have demonstrated that water–rare-earth couplings in the SAA break the rule of “in-between mixing” and synergistically strengthen the local water–rare-earth interactions, surpassing that of any pure individual surface. Mechanistic analysis shows that this anomalous enhancement of water–rare-earth bonding originates from the ability of alloying to further strengthen first-order and second-order quantum electrostatics and suppress remaining covalent components that exist only in the bonding channel of the 2a1 orbital overlapped with the atomic metal states. These findings highlight the importance of SAA-based mixing entropy in reconstructing the underlying mechanism of the anomalous SAA effect. Our investigations not only deepen our understanding of water–rare-earth interactions but also provide a new ground for controllable water activation and the design of rare-earth-based hydrogen evolution catalysts.