Edge-doped substituents as an emerging atomic-level strategy for enhancing M-N4-C single-atom catalysts in electrocatalysis of the ORR, OER, and HER.

M-N₄-C single-atom catalysts (MN₄) have gained attention for their efficient use at the atomic level and adjustable properties in electrocatalytic reactions like the ORR, OER, and HER. Yet, understanding MN₄'s activity origin and enhancing its performance remains challenging. Edge-doped substituents profoundly affect MN₄'s activity, explored in this study by investigating their interaction with MN₄ metal centers in ORR/OER/HER catalysis (Sub@MN₄, Sub = B, N, O, S, CH₃, NO₂, NH₂, OCH₃, SO₄; M = Fe, Co, Ni, Cu). The results show overpotential variations (0 V to 1.82 V) based on Sub and metal centers. S and SO₄ groups optimize FeN₄ for peak ORR activity (overpotential at 0.48 V) and reduce OER overpotentials for NiN₄ (0.48 V and 0.44 V). N significantly reduces FeN₄'s HER overpotential (0.09 V). Correlation analysis highlights the metal center's key role, with ΔG_*H and ΔG_*OOH showing mutual predictability (R² = 0.92). E_g proves a reliable predictor for Sub@CoN₄ (ΔG_*OOH/ΔG_*H, R² = 0.96 and 0.72). Machine learning with the KNN model aids catalyst performance prediction (R² = 0.955 and 0.943 for ΔG_*OOH/ΔG_*H), emphasizing M-O/M-H and the d band center as crucial factors. This study elucidates edge-doped substituents' pivotal role in MN₄ activity modulation, offering insights for electrocatalyst design and optimization.