Too Much of a Good Thing? Assessing Performance Tradeoffs of Two-Electron Compounds for Redox Flow Batteries
Too Much of a Good Thing? Assessing Performance Tradeoffs of Two-Electron Compounds for Redox Flow Batteries
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DOI：
10.1149/1945-7111/abeea3
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发表时间：
2021-01
影响因子：
3.9
通讯作者：
Bertrand J. Neyhouse;Alexis M. Fenton;F. Brushett
中科院分区：
文献类型：
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作者：
Bertrand J. Neyhouse;Alexis M. Fenton;F. Brushett
工程氧化还原活性化合物支持稳定的多电子转移是提高氧化还原液流电池（rfb）能量密度和降低成本的新兴策略。然而，当在不同的氧化还原电位下发生顺序电子转移时，电解质容量的增加伴随着光伏效率的降低，限制了可行的设计空间。为了更好地理解双电子化合物的性能权衡，我们应用理论模型来研究电子转移机制和氧化还原活性物质性质对恒流过程的影响。首先，我们在平面电极上模拟时间电位测定，以了解电化学响应和相关浓度分布如何依赖于热力学、动力学和质量传递因素。其次，使用零维恒流充放电模型，我们评估了这些关键描述符对单个半电池性能的影响。具体来说，我们研究了不同的性质（即两个氧化还原电位的平均值、两个氧化还原电位之间的差值、充电速率、传质速率和比例速率）如何影响电极极化和光伏效率。最后，我们将恒流模型扩展到包括两个半电池中的双电子化合物，展示了整个电池的复合电压损失。这些结果表明多电子化合物的适用性存在局限性，因此，我们提出了分子和系统工程的新方向，可能会改善这些材料在rfb中的前景。
Engineering redox-active compounds to support stable multi-electron transfer is an emerging strategy for enhancing the energy density and reducing the cost of redox flow batteries (RFBs). However, when sequential electron transfers occur at disparate redox potentials, increases in electrolyte capacity are accompanied by decreases in voltaic efficiency, restricting the viable design space. To understand these performance tradeoffs for two-electron compounds specifically, we apply theoretical models to investigate the influence of the electron transfer mechanism and redox-active species properties on galvanostatic processes. First, we model chronopotentiometry at a planar electrode to understand how the electrochemical response and associated concentration distributions depend on thermodynamic, kinetic, and mass transport factors. Second, using a zero-dimensional galvanostatic charge / discharge model, we assess the effects of these key descriptors on performance for a single half-cell. Specifically, we examine how different properties (i.e., average of the two redox potentials, difference between the two redox potentials, charging rate, mass transfer rate, and comproportionation rate) affect the electrode polarization and voltaic efficiency. Finally, we extend the galvanostatic model to include two-electron compounds in both half-cells, demonstrating compounding voltage losses for a full cell. These results evince limitations to the applicability of multi-electron compounds—as such, we suggest new directions for molecular and systems engineering that may improve the prospects of these materials within RFBs.