Single-atom Fe–N–C catalysts have attracted significant attention in the NO_x reduction reaction (NO_xRR). However, the origin of their selectivity in the NO_xRR remains unclear, impeding further advancements in application. Herein, we investigate the potential-driven competitive mechanism for NH₃ and NH₂OH production in the NO_xRR over single-atom pyridinic-FeN₄ and pyrrolic-FeN₄ sites using constant-potential density functional theory calculations. The origin of selectivity in the NO_xRR is linked to the switching of Fe 3d orbitals as they interact with intermediates. The selectivity between NH₃ and NH₂OH is determined by the applied potentials. The pyridinic-FeN₄ predominantly generates NH₃ at higher reduction potentials (−0.6 to −1.2 V, vs SHE), while NH₂OH is favored at lower reduction potentials (0.6 to −0.6 V). The pyrrolic-FeN₄ shows a similar potential-dependent product distribution, with a crossover potential of −1.0 V. The selectivity-determining intermediates (SDIs) in the NO_xRR are *NH₂OH and *NH₂ + *OH. The potential-dependent selectivity is governed by the switching of Fe 3d orbitals interacting with SDIs, from dumbbell-shaped Fe 3dz² to four-leaf clover-like Fe 3dxz, 3dyz, and 3dx²-y², which plays a crucial role in controlling product distribution based on applied potentials. These findings offer new insights into the product selectivity of single-atom catalysts for the NO_xRR.

中文翻译：

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单原子 Fe–N–C 催化剂电化学 NOx 还原选择性的理论见解


单原子 Fe-N-C 催化剂在 NO_x 还原反应 （NO_xRR） 中引起了极大的关注。然而，它们在 NO_xRR 中的选择性来源仍不清楚，阻碍了应用的进一步进展。在此，我们使用恒电位密度泛函理论计算研究了单原子吡啶-FeN₄ 和吡咯-FeN₄ 位点上 NO_xRR 中产生 NH₃ 和 NH₂OH 的电位驱动竞争机制。NO_xRR 中选择性的来源与 Fe 3d 轨道在与中间体相互作用时的切换有关。NH₃ 和 NH₂OH 之间的选择性由施加的电位决定。吡啶-FeN₄ 主要在较高的还原电位（-0.6 至 -1.2 V，与 SHE 相比）下产生 NH₃，而 NH₂OH 在较低的还原电位（0.6 至 -0.6 V）下更受欢迎。吡咯酸 FeN₄ 显示出类似的电位依赖性产物分布，交越电位为 −1.0 V。NO_xRR 中的选择性决定中间体 （SDI） 为 *NH₂OH 和 *NH₂ + *OH。电位依赖性选择性由与 SDI 相互作用的 Fe 3d 轨道的切换控制，从哑铃形 Fe 3dz² 到四叶草状 Fe 3dxz、3dyz 和 3dx^{2-y 2}，这在控制基于施加电位的产物分布中起着至关重要的作用。 这些发现为单原子催化剂对 NO_xRR 的产物选择性提供了新的见解。