The electrochemical reduction of carbon dioxide (CO₂) generating value-added chemicals or fuels using renewable energy resources represents a promising approach to mitigate the greenhouse gases present in the atmosphere. However, a critical challenge to this approach is to develop highly efficient catalysts with minimum energy input and maximum conversion efficiency. Stable and strong electrocatalysts, which can promote the electroreduction of CO₂ beyond the two-electron process to produce various useful products, are highly desirable. Herein, we studied mononuclear and dinuclear complexes of Cr, Mn, Fe, Co and Ni with macrocyclic Schiff-base calixpyrrole ligands, often referred to as Pacman ligands, for their activity towards catalysing the reduction of CO₂ to methane (CH₄) or methanol (CH₃OH). In the case of mononuclear complexes, only one N₄ cavity is occupied by the transition metal. In contrast, in the case of dinuclear complexes, the transition metal is placed in each of the two N₄ cavities of the macrocyclic ligand. Our DFT calculations have shown that the iron-containing mononuclear complex displayed the highest activity and selectivity for the transformation of CO₂ to CH₄ with a very low negative value of limiting potential of −0.24 V. However, in the case of dinuclear complexes, the lowest negative limiting potential was found to be −0.45 V. This work offers a technique for developing electrocatalysts that have great potential for CO₂ reduction reactions.

中文翻译：

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单核和双核Pacman配合物电催化还原CO2的首要原理研究

使用可再生能源对生成增值化学品或燃料的二氧化碳（CO ₂）进行电化学还原，是减轻大气中温室气体排放的一种有前途的方法。然而，该方法的关键挑战是开发具有最小能量输入和最大转化效率的高效催化剂。非常需要稳定且强壮的电催化剂，其可以促进CO ₂的电还原超过双电子过程以产生各种有用的产物。在本文中，我们研究了Cr，Mn，Fe，Co和Ni与大环席夫碱杯with吡咯配体（通常称为Pacman配体）的单核和双核配合物对催化CO ₂还原的活性。生成甲烷（CH ₄）或甲醇（CH ₃ OH）。在单核络合物的情况下，过渡金属仅占据一个N ₄腔。相反，在双核络合物的情况下，过渡金属被置于大环配体的两个N ₄空穴的每一个中。我们的DFT计算表明，含铁单核络合物显示出最高的活性和选择性，可将CO ₂转化为CH ₄具有极低的-0.24 V极限电势负值。但是，在双核络合物的情况下，发现最低的负极限电势为-0.45V。这项工作为开发具有很大CO潜力的电催化剂提供了一种技术。_2个还原反应。