Strain Modulation of Structural Stability and Oxygen Reduction Activity on Fe-Decorated Graphitic Carbon Nitride Nanosheets: An In-Depth DFT Analysis

Strain modulation optimizes catalytic reactivity by reconfiguring geometric and electronic structures at the nanoscale. Due to their mechanical flexibility, graphitic carbon nitride (g-C₃N₄) nanosheets serve as an ideal support for single-atom catalysts (SACs) in the oxygen reduction reaction (ORR). In this study, density functional theory (DFT) calculations are employed to systematically investigate the effects of biaxial and uniaxial strains on the structural stability and ORR activity of Fe-decorated g-C₃N₄. The nanostructured g-C₃N₄ substrate adopts a buckled geometry that dictates the electronic environment of the Fe–N_x active centers. Our results demonstrate that compressive strain regulates the Fe-site electronic configuration by enhancing π back-donation to O₂, which promotes initial activation but overstabilizes the *OH intermediate. This shifts the potential-determining step (PDS) to the *OH desorption, limiting the overall kinetics. In contrast, moderate tensile strain (+4%) optimizes the reaction energetics by moderately weakening the *OH binding, reducing the ORR overpotential by 0.2–0.3 V. These findings highlight the coupling between substrate deformation, electronic states, and catalytic intermediates, demonstrating that mechanical strain engineering is an effective approach for designing high-performance nonprecious metal nanomaterials for the ORR.