First-Principles\nInsights into Tungsten Semicarbide-Based\nSingle-Atom Catalysts: Single-Atom Migration and Mechanisms in Oxygen\nReduction

Abstract

Understanding the structural evolution of single-atom\ncatalysts\n(SACs) in catalytic reactions is crucial for unraveling their catalytic\nmechanisms. In this study, we utilize density functional theory calculations\nto delve into the active phase evolution and the oxygen reduction\nreaction (ORR) mechanism of tungsten semicarbide-based transition\nmetal SACs (TM₁/W₂C). The stable crystal phases\nand optimal surface exposures of W₂C are identified by\nusing <i>ab initio</i> atomistic thermodynamics simulations.\nFocusing on the W-terminated (001) surface, we screen 13 stable TM₁/W₂C variants, ultimately selecting Pt₁/W₂C(001) as our primary model. The surface Pourbaix diagram,\nmapped for this model under ORR conditions, reveals dynamic Pt₁ migration on the surface, triggered by surface oxidation.\nThis discovery suggests a novel single-atom evolution pathway. Remarkably,\nthis single-atom migration behavior is also discerned in seven other\ngroup VIII SACs, enhancing both their catalytic activity and their\nstability. Our findings offer insights into the evolution of active\nphases in SACs, considering substrate structural arrangement, single-atom\nincorporation, and self-optimization of catalysts under various conditions.