The general synthesis and control of the coordination environment of single-atom catalysts (SACs) remains a great challenge. Herein, a general host-guest cooperative protection strategy has been developed to construct SACs by introducing polypyrrole (PPy) into a bimetallic metal-organic framework. As an example, the introduction of Mg2+ in MgNi-MOF-74 extends the distance between adjacent Ni atoms; the PPy guests serve as N source to stabilize the isolated Ni atoms during pyrolysis. As a result, a series of single-atom Ni catalysts (named NiSA -Nx -C) with different N coordination numbers have been fabricated by controlling the pyrolysis temperature. Significantly, the NiSA -N2 -C catalyst, with the lowest N coordination number, achieves high CO Faradaic efficiency (98 %) and turnover frequency (1622 h-1 ), far superior to those of NiSA -N3 -C and NiSA -N4 -C, in electrocatalytic CO2 reduction. Theoretical calculations reveal that the low N coordination number of single-atom Ni sites in NiSA -N2 -C is favorable to the formation of COOH* intermediate and thus accounts for its superior activity.

中文翻译：

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调节MOF模板化单原子镍电催化剂的配位环境以促进CO2还原。

单原子催化剂（SAC）配位环境的一般合成和控制仍然是一个巨大的挑战。在此，已经开发了通过将聚吡咯（PPy）引入双金属金属-有机框架来构建SAC的通用的主客合作保护策略。例如，在MgNi-MOF-74中引入Mg2 +可以延长相邻Ni原子之间的距离。PPy客体充当N源，以在热解过程中稳定分离出的Ni原子。结果，通过控制热解温度，已经制造了一系列具有不同N配位数的单原子Ni催化剂（称为NiSA-Nx-C）。值得注意的是，具有最低N配位数的NiSA -N2-C催化剂可实现高的CO法拉第效率（98％）和周转频率（1622 h-1），在电催化CO2还原方面，远远优于NiSA -N3-C和NiSA -N4-C。理论计算表明，NiSA -N2-C中单原子Ni位的低N配位数有利于COOH *中间体的形成，因此具有较高的活性。