JACS：阳离子特异性吸附增强CO2电还原C-C偶联

研究背景

电化学二氧化碳还原（eCO₂RR）作为一种可持续的方法，在减少碳排放和生产有价值的化学原料方面具有巨大的前景。在所有的eCO₂RR产品中，多碳（C₂₊）产品，如乙醇、乙烯和丙醇，由于其作为化学原料用途而引起了人们极大的兴趣。尽管Cu能够催化eCO₂RR生成C₂₊产物，但Cu电催化剂的选择性有限仍然是一个主要问题。通过引入某些碱性阳离子来调整电极-电解质界面（EEI）的微环境已成为解决这一挑战的有效策略。据报道，在大多数反应条件下，EEI上的Cs⁺和K⁺等大阳离子可以有效地提高C₂₊产物的选择性，而对于Na⁺和Li⁺等小阳离子，需要适当调节反应环境，如在电解质中引入非质子溶剂，以选择性地获得理想的C₂₊产物。此外，在一定条件下，如果没有额外的碱性阳离子，eCO₂RR就不能发生。因此，在eCO₂RR的所有反应条件下，简单地向电解质中加入碱性阳离子通常不会显著改变C₂₊产物选择性，重要的是利用不同调控策略量身定制反应条件，以最大限度地提高产量。为了有效地设计这些调控方法，有必要对其机制进行更深入的解析。    

本文要点

1. 通过恒电位AIMD模拟，研究了C-C偶联过程中界面K⁺离子在Cu表面上的动态行为以及阳离子效应的起源。

2. 研究发现，K⁺很容易在Cu表面与*CO中间体相邻位置发生特异性吸附。在*CO-*CO偶联过程中，K⁺的特异性吸附比非特异性吸附更能提高偶联动力学，由于在K⁺，*CO和Cu位点之间发生了电荷重分布，使偶联能垒降低约0.20 eV。

2. 实验结果表明，使用表面活性剂十六烷基三甲基溴化铵（CTAB）抑制表面K⁺特异性吸附可显著降低C₂产物的法拉第效率，从41.1%降至4.3%，与计算结果一致。

图文内容

Figure 1. (a) Representative snapshot of the constructed EEI model. H, C, O, K, and Cu atoms are shown in white, gray, red, purple, and orange, respectively. (b) Grand free energy profile of K⁺-specific adsorption on Cu(100) and (c) Cu(111) surfaces at −1.5 V_SHE calculated by the “slow-growth” approach. (d) Illustration of the specific adsorption process of the partially dehydrated K⁺ ion. H, C, O, K, and Cu atoms are shown in green, gray, red, purple, and orange, respectively.

Figure 2. Without K⁺ ions in the electrolyte, the grand free energy profile of *CO–*CO coupling on (a) Cu(100) and (b) Cu(111) surfaces at −1.5 V_SHE calculated by the “slow-growth” approach. With K⁺ ions in the electrolyte, the grand free energy profile of *CO–*CO coupling on (c) Cu(100) and (d) Cu(111) surfaces at −1.5 V_SHE. The CV is defined as the distance between the two involved C atoms. (e) Illustration of the K⁺-specific adsorption-assisted *CO–*CO coupling process.

Figure 3. (a) Grand free energy profiles of *CO–*CO coupling on Cu(100) with different K⁺ distributions at −1.5 V_SHE calculated by the “slow-growth” approach. (b) Charge distribution differences between the specifically/quasi-specifically absorbed K⁺ and the reaction environment in the transition state. (c) With specific/quasi-specific adsorption of K⁺, the projected crystal orbital Hamilton population (pCOHP) results of the overlap states between the *C atom and the supporting Cu atom in the transition state. (d) With specific/quasi-specific adsorption of K⁺, the pCOHP results of the overlap states between the *C atom and the K⁺ ion in the transition state.

（图片来源：J. Am. Chem. Soc.）

Figure 5. (a) Nyquist plots of Cu catalyst. (b) Bode plots and the (c) electrochemical double-layer capacitance. (d) Linear scanning voltammetry curves. (e) FEs of different products at −1.0 V vs RHE tested in a three-electrode flow cell system with CuO-derived Cu as the catalyst in a 1.0 M KHCO₃ electrolyte at different concentrations of CTAB. (f) Corresponding partial current densities of C₂H₄ at different concentrations of CTAB.

（图片来源：J. Am. Chem. Soc.）

文献信息

Yanyang Qin, Bao Yu Xia*, Yaqiong Su* et al. Specific Adsorption of Alkaline Cations Enhances CO–CO Coupling in CO₂ Electroreduction. J. Am. Chem. Soc. 2024.

DOI：10.1021/jacs.4c10455

https://doi.org/10.1021/jacs.4c10455

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