Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
Department of Chemical Engineering, University of Illinois at Chicago, Chicago, IL 60607.
Proc Natl Acad Sci U S A. 2017 Oct 17;114(42):E8812-E8821. doi: 10.1073/pnas.1713164114. Epub 2017 Oct 2.
Electrochemical reduction of CO using renewable sources of electrical energy holds promise for converting CO to fuels and chemicals. Since this process is complex and involves a large number of species and physical phenomena, a comprehensive understanding of the factors controlling product distribution is required. While the most plausible reaction pathway is usually identified from quantum-chemical calculation of the lowest free-energy pathway, this approach can be misleading when coverages of adsorbed species determined for alternative mechanism differ significantly, since elementary reaction rates depend on the product of the rate coefficient and the coverage of species involved in the reaction. Moreover, cathode polarization can influence the kinetics of CO reduction. Here, we present a multiscale framework for ab initio simulation of the electrochemical reduction of CO over an Ag(110) surface. A continuum model for species transport is combined with a microkinetic model for the cathode reaction dynamics. Free energies of activation for all elementary reactions are determined from density functional theory calculations. Using this approach, three alternative mechanisms for CO reduction were examined. The rate-limiting step in each mechanism is **COOH formation at higher negative potentials. However, only via the multiscale simulation was it possible to identify the mechanism that leads to a dependence of the rate of CO formation on the partial pressure of CO that is consistent with experiments. Simulations based on this mechanism also describe the dependence of the H and CO current densities on cathode voltage that are in strikingly good agreement with experimental observation.
使用可再生电能电化学还原 CO 有望将 CO 转化为燃料和化学品。由于这个过程很复杂，涉及到大量的物种和物理现象，因此需要全面了解控制产物分布的因素。虽然最合理的反应途径通常是从量子化学计算最低自由能途径来确定的，但当替代机制中吸附物种的覆盖率有很大差异时，这种方法可能会产生误导，因为基本反应速率取决于参与反应的物种的速率系数和覆盖率的乘积。此外，阴极极化会影响 CO 还原的动力学。在这里，我们提出了一个用于在 Ag(110)表面上进行电化学还原 CO 的从头算模拟的多尺度框架。物种传输的连续体模型与阴极反应动力学的微观动力学模型相结合。所有基本反应的活化自由能都是从密度泛函理论计算中确定的。使用这种方法，研究了 CO 还原的三种替代机制。每个机制的速率限制步骤都是在更高的负电势下形成 **COOH。然而，只有通过多尺度模拟，才有可能确定导致 CO 形成速率与 CO 分压相关的机制，这与实验结果一致。基于该机制的模拟还描述了 H 和 CO 电流密度随阴极电压的变化，与实验观察结果非常吻合。
