The porphyrin-based MOFs formed by combining Zr-6 clusters and porphyrin carboxylic acids with clear M-N-4 active centers show unique advantages in electrocatalytic reduction of CO2 (CO2RR). However, its conductivity is still the bottleneck that limits its catalytic activity due to the electrical insulation of the Zr cluster. Therefore, the porphyrin-based MOFs of PCN-222(M) (M = Mn, Co, Ni, Zn) with explicit M-N-4 coordination were combined with the highly conductive material carbon nanotube (CNT) for discussing the influence of metal centers on the CO2RR performance based on theoretical calculations and experimental observations. The results show that the PCN-222(Mn)/CNT, PCN-222(Co)/CNT, and PCN-222(Zn)/CNT all exhibit high selectivity to CO (FECO > 80%) in the range of -0.60 to -0.70 V vs. RHE. The FECOmax of PCN-222(Mn)/CNT (-0.60 V vs. RHE), PCN-222(Co)/CNT (-0.65 V vs. RHE), and PCN-222(Zn)/CNT (-0.70 V vs. RHE) are 88.5%, 89.3% and 92.5%, respectively. The high catalytic activity of PCN-222(Mn)/CNT and PCN-222(Co)/CNT comes from the excellent electron mobility of their porphyrin rings and their low Delta G(*COOH) (0.87 and 0.58 eV). It reveals that the strength of backbonding pi of the transition metal and its influence on the electron mobility in the porphyrin ring can affect its CO2RR activity.

中文翻译：

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阐明金属中心在 PCN-222(M) 卟啉基 MOF 中用于电化学还原 CO2 的作用

由 Zr-6 簇和卟啉羧酸结合形成的卟啉基 MOFs 具有清晰的 MN-4 活性中心，在电催化还原 CO2 (CO2RR) 方面显示出独特的优势。然而，由于Zr簇的电绝缘性，其导电性仍然是限制其催化活性的瓶颈。因此，将具有显式 MN-4 配位的 PCN-222(M) (M = Mn、Co、Ni、Zn) 卟啉基 MOF 与高导电材料碳纳米管 (CNT) 相结合，以讨论金属中心的影响基于理论计算和实验观察的 CO2RR 性能。结果表明，PCN-222(Mn)/CNT、PCN-222(Co)/CNT 和 PCN-222(Zn)/CNT 在-0.60 范围内均表现出对 CO 的高选择性（FECO > 80%）至 -0.70 V 与 RHE。PCN-222(Mn)/CNT 的 FECOmax（-0.60 V vs. RHE)、PCN-222(Co)/CNT（-0.65 V vs. RHE）和 PCN-222(Zn)/CNT（-0.70 V vs. RHE）分别为 88.5%、89.3% 和 92.5%。PCN-222(Mn)/CNT 和 PCN-222(Co)/CNT 的高催化活性来自于其卟啉环出色的电子迁移率和低 Delta G(*COOH)（0.87 和 0.58 eV）。结果表明，过渡金属的背键强度及其对卟啉环中电子迁移率的影响会影响其CO2RR活性。