氧电化学还原过程中异质单原子催化剂的位间距离依赖性和磁转变效应
Unravelling Distance-Dependent Inter-Site Interactions and Magnetic Transition Effects of Heteronuclear Single Atom Catalysts on Electrochemical Oxygen Reduction
摘要：
在高负载范围内，单原子催化剂（SAC）之间的位点间相互作用对于调节催化性能至关重要。然而，对这种相互作用及其距离依赖效应的理解仍然是难以捉摸的，特别是对于异质性SAC。在这项研究中，我们揭示了距离依赖性的中心间相互作用的SAC的催化性能的影响。采用密度泛函理论，系统研究了氮掺杂石墨烯（FeN 4-C和CoN 4-C）负载的铁钴异质单原子的氧还原反应（ORR）.我们发现，随着Fe和Co SAC之间的距离减小，FeN 4-C表现出降低的催化活性，这可以通过轴向羟基配体的存在来减轻，而CoN 4-C的活性显示出火山式的演变，在中间距离处达到最佳。我们进一步揭示了ORR中间吸附物吸附后向高自旋态的转变是导致FeN 4-C和CoN 4-C在短的位点间距离下活性降低的原因。这种高自旋态的转变也被发现显着移动羟基（*OH）和氢过氧（*OOH）吸附物之间的线性关系。这些发现不仅揭示了异质性SAC之间的距离依赖性位点间相互作用的SAC特异性效应，而且为改变多电子化学反应中观察到的长期线性关系铺平了道路。
英文摘要：
Inter-site interactions between single atom catalysts (SACs) in the high loading regime are critical to tuning the catalytic performance. However, the understanding on such interactions and their distance dependent effects remains elusive, especially for the heteronuclear SACs. In this study, we reveal the effects of the distance-dependent inter-site interaction on the catalytic performance of SACs. Using the density functional theory calculations, we systematically investigate the heteronuclear iron and cobalt single atoms co-supported on the nitrogen-doped graphene (FeN4-C and CoN4-C) for oxygen reduction reaction (ORR). We find that as the distance between Fe and Co SACs decreases, FeN4-C exhibits a reduced catalytic activity, which can be mitigated by the presence of an axial hydroxyl ligand, whereas the activity of CoN4-C shows a volcano-like evolution with the optimum reached at the intermediate distance. We further unravel that the transition towards the high-spin state upon adsorption of ORR intermediate adsorbates is responsible for the decreased activity of both FeN4-C and CoN4-C at short inter-site distance. Such high-spin state transition is also found to significantly shift the linear relation between hydroxyl (*OH) and hydroperoxyl (*OOH) adsorbates. These findings not only shed light on the SAC-specific effect of the distance-dependent inter-site interaction between heteronuclear SACs, but also pave a way towards shifting the long-standing linear relations observed in multiple-electron chemical reactions.
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