A bottom-up, multi-scale theory for transient mass transport of redox-active species through porous electrodes beyond the pseudo-steady limit
A bottom-up, multi-scale theory for transient mass transport of redox-active species through porous electrodes beyond the pseudo-steady limit
复制标题
自下而上的多尺度理论，用于氧化还原活性物质通过多孔电极超越伪稳态极限的瞬态质量传递
DOI：
10.1016/j.jpowsour.2023.232756
复制
发表时间：
2023
影响因子：
9.2
通讯作者：
Smith, Kyle C.
中科院分区：
文献类型：
--
作者：
Hamid, Md Abdul;Smith, Kyle C.
提出了氧化还原活性电解质在随时间变化的施加电流下流经多孔电极的动态响应的新理论。这是通过引入某些结合了孔隙尺度传输物理学的频率相关传递函数（TF）来完成的。一个 TF（称为光谱舍伍德数）将薄膜传质定律 (FLoMT) 扩展到瞬态条件。另一个 TF 捕获由孔隙尺度速度/浓度梯度引起的溶质平流的加速/抑制。显示了横流中实心圆柱体的频率相关 TF 的数值结果，以代表液流电池 (FB) 中常用的多孔电极。可以观察到随着频率的增加，从无滞后响应到半无限 Warburg 响应的转变发生的频谱区域。还将这些 TF 嵌入到放大模型中，以获得 FB 的时域响应。尽管传统 FLoMT 模型存在系统性过度预测，但在没有可调参数的情况下，该模型预测的极化与瞬态 FB 实验一致。浓差极化和反应物浓度的分析也用于构建操作空间的无量纲图。这些预测表明，即使电流超过时不变 FLoMT 预期的极限电流（没有溶质平流抑制/加速），快速电流波动也会持续，这还表明对电化学转换和分离装置的影响。
New theory is presented for the dynamic response of redox-active electrolyte flowing through porous electrodes under time-dependent applied current. This is done by introducing certain frequency-dependent transfer functions (TFs) that incorporate pore-scale transport physics. One TF – dubbed the spectral Sherwood number – extends the film law of mass transfer (FLoMT) to transient conditions. Another TF captures the acceleration/suppression of solute advection that results from pore-scale velocity/concentration gradients. Numerical results are shown for the frequency-dependent TFs of solid cylinders in crossflow to represent porous electrodes commonly used in flow batteries (FBs). Spectral regions are observed where a transition from lagless response to semi-infinite Warburg response occurs with increasing frequency. The embedding of these TFs into an up-scaled model is also formulated to obtain the time-domain response of FBs. Without adjustable parameters this model predicts polarization in agreement with transient FB experiments, despite systematic overprediction by the conventional FLoMT model. Analysis of concentration polarization and reactant concentration is also used to construct non-dimensional maps of operational space. These predictions show that fast current fluctuations are sustained even when current exceeds the limiting current expected from the time-invariant FLoMT without solute advection suppression/acceleration, suggesting implications for electrochemical conversion and separations devices in addition.