Exploring highly active and cost-efficient single-atom catalysts (SACs) for oxygen reduction reaction (ORR) is critical for the large-scale application of Zn–air battery. Herein, density functional theory (DFT) calculations predict that the intrinsic ORR activity of the active metal of SACs follows the trend of Co > Fe > Ni ≈ Cu, in which Co SACs possess the best ORR activity due to its optimized spin density. Guided by DFT calculations, four kinds of transition metal single atoms embedded in 3D porous nitrogen-doped carbon nanosheets (MSAs@PNCN, M = Co, Ni, Fe, Cu) are synthesized via a facile NaCl-template assisted strategy. The resulting MSAs@PNCN displays ORR activity trend in lines with the theoretical predictions, and the Co SAs@PNCN exhibits the best ORR activity (E_1/2 = 0.851 V), being comparable to that of Pt/C under alkaline conditions. X-ray absorption fine structure (XAFS) spectra verify the atomically dispersed Co-N₄ sites are the catalytically active sites. The highly active CoN₄ sites and the unique 3D porous structure contribute to the outstanding ORR performance of Co SAs@PNCN. Furthermore, the Co SAs@PNCN catalyst is employed as cathode in Zn–air battery, which can deliver a large power density of 220 mW cm^–2 and maintain robust cycling stability over 530 cycles.

中文翻译：

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锚定在 3D 氮掺杂多孔碳纳米片上的过渡金属（Co、Ni、Fe、Cu）单原子催化剂作为锌空气电池的高效氧还原电催化剂

探索用于氧还原反应（ORR）的高活性且具有成本效益的单原子催化剂（SAC）对于锌空气电池的大规模应用至关重要。在此，密度泛函理论 (DFT) 计算预测 SACs 的活性金属的本征 ORR 活性遵循 Co > Fe > Ni ≈ Cu 的趋势，其中 Co SACs 由于其优化的自旋密度而具有最佳的 ORR 活性。在 DFT 计算的指导下，通过简便的 NaCl 模板辅助策略合成了嵌入 3D 多孔氮掺杂碳纳米片 (MSAs@PNCN, M = Co, Ni, Fe, Cu) 中的四种过渡金属单原子。得到的 MSAs@PNCN 显示出与理论预测一致的 ORR 活性趋势，Co SAs@PNCN 表现出最好的 ORR 活性 ( E _1/2 = 0.851 V)，与碱性条件下的 Pt/C 相当。X射线吸收精细结构（XAFS）光谱证实原子分散的Co-N ₄位点是催化活性位点。高活性的 CoN ₄位点和独特的 3D 多孔结构有助于 Co SAs@PNCN 出色的 ORR 性能。^{此外，Co SAs@PNCN 催化剂用作锌空气电池的阴极，可提供 220 mW cm -2}的大功率密度，并在 530 次循环后保持稳健的循环稳定性。