Johnson Evan, Haussener Sophia
Laboratory of Renewable Energy Science and Engineering, École Polytechnique Fédérale de Lausanne, Station 9, 1015 Lausanne, Switzerland.
J Phys Chem C Nanomater Interfaces. 2024 Jun 14;128(25):10450-10464. doi: 10.1021/acs.jpcc.4c03469. eCollection 2024 Jun 27.
In the field of electrochemical CO reduction, both continuum models and molecular dynamics (MD) models have been used to understand the electric double layer (EDL). MD often focuses on the region within a few nm of the electrode, while continuum models can span up to the device level (cm). Still, both methods model the EDL, and for a cohesive picture of the CO electrolysis system, the two methods should agree in the regions where they overlap length scales. To this end, we make a direct comparison between state-of-the-art continuum models and classical MD simulations under the conditions of CO reduction on a Ag electrode. For continuum modeling, this includes the Poisson-Nernst-Planck formulation with steric (finite ion size) effects, and in MD the electrode is modeled with the constant potential method. The comparison yields numerous differences between the two modeling methods. MD shows cations forming two adsorbed layers, including a fully hydrated outer layer and a partial hydration layer closer to the electrode surface. The strength of the inner adsorbed layer increases with cation size (Li < Na < K < Cs) and with more negative applied potentials. Continuum models that include steric effects predict CO to be mostly excluded within 1 nm of the cathode due to tightly packed cations, yet we find little evidence to support these predictions from the MD results. In fact, MD shows that the concentration of CO increases within a few Å of the cathode surface due to interactions with the Ag electrode, a factor not included in continuum models. The EDL capacitance is computed from the MD results, showing values in the range of 7-9 μF cm, irrespective of the electrolyte concentration, cation identity, or applied potential. The direct comparison between the two modeling methods is meant to show the areas of agreement and disagreement between the two views of the EDL, so as to improve and better align these models.
在电化学CO还原领域，连续介质模型和分子动力学（MD）模型都已被用于理解双电层（EDL）。MD通常关注电极表面几纳米范围内的区域，而连续介质模型可以扩展到器件级别（厘米）。尽管如此，这两种方法都对双电层进行建模，为了全面了解CO电解系统，在长度尺度重叠的区域，这两种方法应该是一致的。为此，我们在Ag电极上CO还原的条件下，对先进的连续介质模型和经典MD模拟进行了直接比较。对于连续介质建模，这包括考虑空间位阻（有限离子尺寸）效应的泊松-能斯特-普朗克公式，在MD中，电极采用恒电位法建模。比较结果显示了这两种建模方法之间的许多差异。MD显示阳离子形成两个吸附层，包括一个完全水合的外层和一个更靠近电极表面的部分水合层。内层吸附层的强度随阳离子尺寸（Li < Na < K < Cs）和更负的外加电位而增加。考虑空间位阻效应的连续介质模型预测，由于阳离子紧密堆积，CO在阴极1 nm范围内大多被排除，但我们从MD结果中几乎找不到支持这些预测的证据。事实上，MD表明，由于与Ag电极的相互作用，CO在阴极表面几埃范围内的浓度增加，而这一因素在连续介质模型中并未考虑。根据MD结果计算出的双电层电容，显示其值在7 - 9 μF/cm范围内，与电解质浓度、阳离子种类或外加电位无关。这两种建模方法的直接比较旨在展示双电层两种观点之间的一致和不一致之处，以便改进和更好地校准这些模型。
