Probing Redox Properties of Extreme Concentrations Relevant for Nonaqueous Redox-Flow Batteries
Probing Redox Properties of Extreme Concentrations Relevant for Nonaqueous Redox-Flow Batteries
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DOI：
10.1021/acsaem.2c03712
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发表时间：
2023-03
影响因子：
6.4
通讯作者：
Nathan C Stumme;A. Perera;A. Horvath;Sashen Ruhunage;Darby H. Duffy;Elise M. Koltonowski;Jackson Tupper;Chad Dzierba;Alie D. McEndaffer;Craig M. Teague;C. Risko;S. Shaw
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文献类型：
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作者：
Nathan C Stumme;A. Perera;A. Horvath;Sashen Ruhunage;Darby H. Duffy;Elise M. Koltonowski;Jackson Tupper;Chad Dzierba;Alie D. McEndaffer;Craig M. Teague;C. Risko;S. Shaw
氧化还原液流电池是一种新兴的储能技术，可以与间歇性可再生能源技术配对。然而，仍然需要了解组成阴极液和阳极液的溶剂、电解盐和氧化还原活性分子之间的物理化学关系。为了检验这种关系，我们详细地进行了一项系统的研究，其中氧化还原活性分子2，2，6，6-四甲基哌啶1-氧基(TEMPO)和TBAPF6电解盐的浓度在乙腈中的浓度从1 mM到超过1000 mM不等。研究了三个系列：(1)在保持TBAPF6浓度不变的情况下改变TEMPO的浓度；(2)在保持TEMPO浓度不变的情况下改变TBAPF6的浓度；(3)在TBAPF6：TEMPO的比例为5：1的情况下同时改变TEMPO和TBAPF6的浓度。来自宏微电极的循环伏安数据被用来量化扩散系数和非均相电子转移速率，并将这些度量与电导率和粘度联系起来，以在整个浓度范围内显示出明确的趋势。通过振动光谱和分子动力学(MD)模拟，揭示了导致物理性质变化的基本化学作用。体系的电导率和粘度的趋势与扩散系数和非均相电子转移速率的趋势成反比。直观地，TEMPO浓度越低，TBAPF6浓度越高，扩散和电子转移速度越快，大多数条件都落在文献值的大致附近(k0=0.10.5 cm/S，D≈(2.04.0)×10-5cm2/S)。在最高的TBAPF6浓度下，振动光谱和分子动力学模拟表明分子间的相互作用更加细微，溶剂化和离子配对效应开始影响电化学和物理性质。这种功能方法包括电化学和物理表征，结合分子动力学模拟，为系统地研究氧化还原液流电池应用系统提供了模板。
Redox-flow batteries are an emerging energy storage technology that can pair with intermittent renewable energy technologies. There remains a need, however, to understand physicochemical relationships among the solvent, electrolyte salt, and redox-active molecules that comprise catholyte and anolyte solutions. To examine this relationship, we detail a systematic study wherein the concentrations of the redox-active molecule 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and TBAPF6electrolyte salts are varied over concentrations of 1 mM to over 1000 mM in acetonitrile. Three series were investigated: (1) varying the concentration of TEMPO while holding the concentration of TBAPF6constant, (2) varying the concentration of TBAPF6while holding the concentration of TEMPO constant, and (3) varying both the concentration of TEMPO and TBAPF6with a 5:1 TBAPF6:TEMPO ratio. Cyclic voltammetry data from macro- and microelectrodes were used to quantify diffusion coefficients and heterogeneous electron transfer rates, and these metrics were connected to the conductivity and viscosity to develop clear trends over the entire concentration range. Fundamental chemical interactions that lead to changes in physical properties were implicated via vibrational spectroscopy and molecular dynamics (MD) simulations. Trends in conductivity and viscosity for systems were inversely related and correlated to trends in diffusion coefficients and heterogeneous electron transfer rates. Intuitively, faster diffusion and electron-transfer rates occurred with lower TEMPO concentrations and higher TBAPF6concentrations, with the majority of conditions falling in the general proximity of literature values (k0= 0.1–0.5 cm/s,D≈ (2.0–4.0) × 10–5cm2/s). At the highest TBAPF6concentrations, vibrational spectroscopy and MD simulations show that intermolecular interactions were more nuanced, and solvation and ion-pairing effects begin to influence electrochemical and physical properties. This functional approach including electrochemical and physical characterization paired with MD simulations provides a template for methodically studying systems for redox flow battery applications.