The construction of artificial solar fuel generating systems requires the heterogenization of large quantities of catalytically active sites on electrodes. In that sense, metal–organic frameworks (MOFs) have been utilized to assemble unpreceded concentration of electrochemically active molecular catalysts to drive energy-conversion electrocatalytic reactions. However, despite recent advances in MOF-based electrocatalysis, so far no attempt has been made to exploit their unique chemical modularity in order to tailor the electrocatalytic function of MOF-anchored active sites at the molecular level. Here, we show that the axial coordination of electron-donating ligands to active MOF-installed Fe-porphyrins dramatically alters their electronic properties, accelerating the rates of both redox-based MOF conductivity and the electrocatalytic oxygen reduction reaction (ORR). Additionally, electrochemical characterizations show that in multiple proton-coupled electron transfer reactions MOF-based redox hopping is not the only factor that limits the overall electrocatalytic rate. Hence, future efforts to enhance the efficiency of electrocatalytic MOFs should also consider other important kinetic parameters such as the rate of proton-associated chemical steps as well as mass-transport rates of counterions, protons, and reactants toward catalytically active sites.

中文翻译：

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通过配体轴向配位在铁卟啉基金属有机骨架中的活性位点调制：加速电催化和电荷传输动力学

人造太阳能燃料发电系统的构建需要电极上大量催化活性位点的异质化。从这个意义上说，金属有机骨架（MOF）已被用于组装前所未有的电化学活性分子催化剂浓度，以驱动能量转换电催化反应。然而，尽管基于 MOF 的电催化取得了最新进展，但迄今为止还没有尝试利用其独特的化学模块性来在分子水平上定制 MOF 锚定活性位点的电催化功能。在这里，我们表明给电子配体与活性 MOF 安装的 Fe-卟啉的轴向配位显着改变了它们的电子特性，加快基于氧化还原的 MOF 电导率和电催化氧还原反应 (ORR) 的速率。此外，电化学表征表明，在多个质子耦合电子转移反应中，基于 MOF 的氧化还原跳跃并不是限制整体电催化速率的唯一因素。因此，未来提高电催化 MOF 效率的努力还应考虑其他重要的动力学参数，例如质子相关化学步骤的速率以及反离子、质子和反应物向催化活性位点的传质速率。