Chernyshova Irina V, Ponnurangam Sathish
Department of Earth and Environmental Engineering, Columbia University, New York, NY, USA.
Phys Chem Chem Phys. 2019 Apr 24;21(17):8797-8807. doi: 10.1039/c8cp07807f.
Carboxylate *CO2- has recently been identified as the first intermediate of the CO2 electroreduction independent of the reaction pathway. However, on the fundamental level, the structural and electronic properties of *CO2- remain poorly understood especially under the electrocatalytic conditions, which limits our capacity to rationally control the transformation of this reaction intermediate to CO or formate. To close this gap, we model using density functional theory (DFT) the interactions of *CO2- with the copper Cu(111) surface and a co-adsorbed sodium cation in the electric double layer (EDL), as well as the effects of electrode potential on these interactions. We demonstrate that *CO2- is activated by a co-adsorbed alkali cation most strongly when it forms with the cation a noncovalent bond (ion pair), where the cation is coordinated in the on-top position. The most stable structure of this ion pair with a sodium cation is hydration-shared. An external negative electric field not only enhances activation of *CO2- but also tilts it in the *CO2- plane, elongating the metal-C bond and contracting the metal-O bond. This tilting facilitates hydrogenation of the C atom and dissociation of the surface-coordinated C-O bond. Based on a detailed analysis of the projected density of states (pDOS), we interpret these findings in terms of electrostatic and chemical effects. The provided insights can help understand the relationship between properties of the catalytic system and its catalytic activity in the CO2 conversion to CO and formate, and hence help develop new CO2 electroreduction catalysts.
羧酸盐CO2-最近被确定为二氧化碳电还原的首个中间体，与反应路径无关。然而，在基础层面上，CO2-的结构和电子性质仍然了解甚少，尤其是在电催化条件下，这限制了我们合理控制该反应中间体转化为CO或甲酸盐的能力。为了填补这一空白，我们使用密度泛函理论（DFT）对CO2-与铜Cu(111)表面以及双电层（EDL）中共吸附的钠离子之间的相互作用，以及电极电位对这些相互作用的影响进行了建模。我们证明，当CO2-与阳离子形成非共价键（离子对）时，共吸附的碱金属阳离子对CO2-的活化作用最强，此时阳离子以顶位配位。这种与钠离子形成的离子对最稳定的结构是水合共享的。外部负电场不仅增强了CO2-的活化作用，还使其在*CO2-平面内倾斜，拉长了金属-C键并缩短了金属-O键。这种倾斜促进了C原子的氢化和表面配位的C-O键的解离。基于对投影态密度（pDOS）的详细分析，我们从静电和化学效应的角度解释了这些发现。所提供的见解有助于理解催化体系的性质与其在CO2转化为CO和甲酸盐过程中的催化活性之间的关系，从而有助于开发新型的CO2电还原催化剂。
