Water Bonding on Close-Packed Surfaces of Rare-Earth Metals (Sc, Y, La) Renews Existing Water-Metal Bonding Picture

Our knowledge of water bonding on metal surfaces is ruled by the coexistence of covalent and electrostatic nature in water-metal interactions, which leads to the well-known, preferred flat geometry on transition metal surfaces. Using density functional theory (DFT) calculations, herein we have shown that this picture has to be modified for water bonding on Sc(0001), Y(0001), and La(0001), where upright water orientation has been surprisingly found to preferentially coexist with the flat geometry on the rare-earth metal surfaces. Our investigations have proved that both water orientations on the rare-earth metal surfaces originate from unique bonding mechanisms that do not exist in water adsorption on any late transition metal surfaces. In this unique bonding picture, covalent components are evidently absent in the water-metal interactions, which are overwhelmingly dominated by the first-order quantum electrostatics featured by two nearly separated potential wells in the water-metal bonds and by the second-order quantum electrostatics featured by alternating charge depletion and accumulation regions in interference. The new picture not only advances our understanding of how water makes bonds with earlier transition metal surfaces but also lays a physical basis for improving catalytic performance of the rare-earth-metal-based green catalysts for clean energy.