Unlocking Deep Carbonation in γ‐C ₂ S by Iron Dopant: Suppressing Surface Reaction to Promote Dissolution–Precipitation

The rational design of cementitious materials for enhanced CO 2 sequestration hinges on atomic‐level control of reaction pathways. While doping is a promising strategy, its precise mechanistic role remains largely uncharted. Herein, we unravel the atomistic mechanism by which iron (Fe) doping fundamentally steers the carbonation process of γ‐dicalcium silicate (γ‐C 2 S). Through well‐defined ab initio calculations with on‐the‐fly probability enhanced sampling, we demonstrate that Fe preferentially substitutes for surface Si site, forming stable [FeO 4 ] tetrahedra. This substitution induces a localized charge redistribution that enhances surface oxygen electrophilicity, establishing a dual pathway for water hydroxylation that dramatically accelerates hydration and Ca 2 + dissolution. Paradoxically, while the Fe sites activate CO 2 , they instigate a competitive adsorption at the reactive centers, where the strongly bound H 2 O molecules raise the energy barrier for direct surface carbonation. This effectively suppresses the kinetically limited route and promotes the thermodynamically favored dissolution‐precipitation pathway, leading to a higher overall carbonation degree. This work provides a foundational principle for the targeted design of high‐performance carbon‐capture materials through electronic structure modulation.