Abstract
Despite the recent surge in exploration of transition metal single-atom catalysts (SACs), rare earth (RE)-SACs remain relatively understudied. In this work, we consider two lighter RE-SACs (La and Ce) and two heavier RE-SACs (Sm, and Gd) supported on two-dimensional heptazine based graphitic carbon nitride (g-C3N4) monolayer. Known for its inherent photoactive properties, g-C3N4 monolayer turns out to be a suitable support to decorate RE single-atoms, maintaining high structural and thermal stability without forming metal clusters. Both flat and buckled configurations of the g-C3N4 and RE single-atom-decorated g-C3N4 surfaces are systematically investigated. The metal-support interactions in all the RE-SACs are characterized through electronic structure analyses. Heavier RE-SACs (Sm and Gd) exhibit stronger metal-support interactions due to substantial orbital overlap, resulting from the pronounced spin polarization of their 4f orbitals. Compared to pristine g-C3N4, RE single-atom-decorated surfaces exhibit enhanced photo-responsive characteristics across the IR-visible-UV light spectrum. Water molecule adsorption is weaker on heavier RE-SACs (Sm and Gd) than on lighter RE-SACs (La and Ce). However, heavier RE-SACs show more negative reaction energies and lower activation energy barriers, corroborating better thermodynamic and kinetic feasibility of the water molecule cleavage process. Free energy pathways for the hydrogen and oxygen evolution reactions (HER and OER) demonstrate significantly lower overpotentials for heavier RE-SACs compared to lighter RE-SACs. Overall, the stronger metal-support interactions in heavier RE-SACs correlate with their superior catalytic activity.
Published Version
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