二氧化碳减排模型中经常误用的表面电荷边界条件,The Journal of Physical Chemistry C

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二氧化碳减排模型中经常误用的表面电荷边界条件
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2023-09-08 , DOI: 10.1021/acs.jpcc.3c05364
Evan F. Johnson ₁ , Etienne Boutin ₁ , Sophia Haussener ₁

Affiliation

Poisson-Nernst-Planck 方程已用于模拟电化学 CO ₂还原中的物质传递，其中表面电荷边界条件解释了跨 Stern 层的电势降。对已发表模型的直接比较表明，Stern 层内的相对介电常数在整个文献中的应用不一致，其值范围为 6 到 80.1。事实上，大多数研究使用Stern层内的纯水或电解质介电常数值，这意味着Stern层电容在100–200 μF cm ^–2范围内。这远远高于双电层基础实验中测得的斯特恩层电容，通常在 20–25 μF cm ^{–2范围内}。使用如此高的电容会使扩散层中的电场增压，导致高估电解质阳离子浓度、极端 pH 和 pOH 值，并且（如果包括空间效应）大大低估反应平面上的 CO 2_浓度。这种差异可以追溯到表面电荷边界条件，这将在本文中详细解释。先前发布的使用如此高的斯特恩层电容或介电常数的CO ₂ R模型预计会高估双电层的影响。

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Surface Charge Boundary Condition Often Misused in CO2 Reduction Models

The Poisson–Nernst–Planck equations have been used to model species transport in electrochemical CO₂ reduction, where the surface charge boundary condition accounts for the potential drop across the Stern layer. A direct comparison of the published models reveals the relative permittivity inside the Stern layer has been applied inconsistently across the literature, with values ranging from 6 to 80.1. In fact, a majority of studies use the pure water or electrolyte permittivity value inside the Stern layer, implying a Stern layer capacitance in the range of 100–200 μF cm^–2. This is far higher than the Stern layer capacitances measured in fundamental experiments of the electric double layer, typically in the range of 20–25 μF cm^–2. Using such a high capacitance supercharges the electric field in the diffuse layer, leading to an overestimate of the electrolyte cation concentration, extreme pH and pOH values, and─if steric effects are included─a vast underestimation of the CO₂ concentration at the reaction plane. The discrepancy can be traced back to the surface charge boundary condition, which is explained in detail herein. Previously published CO₂R models that used such a high Stern layer capacitance or permittivity are expected to have overpredicted the effects of the electric double layer.

更新日期：2023-09-08

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