在CO2还原反应(CO2RR)应中,单原子催化剂被认为是很有前途的电催化剂.Co-N4活性位点因其优异的CO选择性和活性而受到广泛关注.然而,Co位点的局部配位环境与CO2RR途径之间的相关性尚不明确.本文采用密度泛函理论(DFT)计算,研究了含1,10-菲咯啉基底的N4-大环配体(Co-N4-CPY)负载的CoN4位点上的CO2RR路径.该模型的平面空间构型使其具有高度离域的π电子轨道,可以通过π-π相互作用更好地与底物相互作用.在相对可逆氢电极(RHE)为-0.70 V时,最大CO的法拉第效率为96％,CO的转换频率为9.59 s1.众所周知,单原子位点的局部配位环境可以进一步优化电催化性能.因此,本文还研究了N被O(Co-N3O-CPY)和C(Co-N3C-CPY)取代的单原子Co位点的局部配位环境.计算结果表明,Co-N4,Co-N3O和Co-N3C位点的键长相差不大,而且其结合能都较大,意味着它们具有良好的稳定性.Co-N3C-CPY,Co-N3O-CPY和Co-N4-CPY的投影态密度(PDOS)、电荷密度差分和晶体轨道哈密顿布居(COHP)显示,C和O配位均打破了初始CoN4配体场的对称性,并诱发了Co原子的电荷再分布.Co原子与配位原子间的相互作用由强到弱依次为Co-C键、Co-N键和Co-O键,这与电负性O＞N＞C相反.通过分析CO2RR过程的吉布斯自由能变化,确定了Co-N4-CPY的主要产物为CO.当Co-N4位点的局部配位环境改变后,Co-N3O位点上有利于*COOH的形成,而Co-N3C位点对碳氢化合物(CH3OH或CH4)有更高的选择性.这是由于CO2在Co-N3O位点上更容易质子化形成*OCHO,从而有利于HCOOH的形成.而在Co-N3C位点上时,由于*CO难以脱附,*CO将进一步质子化,最终形成CH3OH或CH4.CO2质子化形成*COOH或*OCHO的PDOS显示,在Co位上吸附之前,*OCHO的自旋密度是对称的,而*COOH的自旋密度是不对称的.对于催化剂而言,只有Co-N3O-CPY的自旋密度是对称的,因此容易形成*OCHO中间体.Co-3d轨道与*COOH的C-2p轨道和*OCHO的O-2p轨道的相互作用也体现了这一关系.本工作为单原子位点的局部配位环境与CO2RR途径之间的关系提供了一个新的视角.“,”Single-atom catalysts have been proposed as promising electrocatalysts for CO2 reduction reactions(CO2RR).Co-N4 active sites have attracted wide attention owing to their excellent CO selectivity and activity.However,the effect of the local coordination environment of Co sites on CO2 reduction reaction pathways is still unclear.In this study,we investigated the CO2 reduction reaction path-ways on Co-N4 sites supported on conjugated N4-macrocyclic ligands with 1,10-phenanthroline subunits (Co-N4-CPY) by density functional theory calculations.The local coordination environment of single-atom Co sites with N substituted by O (Co-N3O-CPY) and C (Co-N3C-CPY) was studied for comparison.The calculation results revealed that both C and O coordination break the symmetry of the primary CoN4 ligand field and induce charge redistribution of the Co atom.For Co-N4-CPY,CO was confirmed to be the main product of CO2RR.HCOOH is the primary product of Co-N3O-CPY because of the greatly increased energy barrier of CO2 to *COOH.Although the energy barrier of CO2 to *COOH is reduced on Co-N3C-CPY,the desorption process of*CO becomes more difficult.CH3OH(or CH4) are obtained by further *CO hydrogenation reduction when using Co-N3C-CPY.This work provides new insight into the effect of the local coordination environment of single-atom sites on CO2 reduction reaction pathways.