An Aqueous Redox Flow Battery (ARFB) has emerged as a sustainable option for large-scale energy storage systems due to its relatively low cost and abundant raw materials. However, there exists a pressing need to enhance its power density and energy efficiency by addressing limitations such as low stability and poor solubility of redox-active species. In this study, we present a systematic analysis of an asymmetric viologen-based negolyte named MMV (1-methyl-4,4′-bipyridinium iodide) and its detailed comparative study with N,N′-dimethyl-4,4′-bipyridinium diiodide (dimethyl viologen (DMV)). Following extensive electrochemical characterization, we constructed an alkaline MMV battery paired with the potassium ferro/ferricyanide posolyte at a higher concentration (0.8 M), yielding a cell voltage of 1.25 V, nearly equivalent to those of vanadium RFBs. Remarkably, long-term cycling with 97% coulombic efficiency (CE) and 71% energy efficiency (EE) was achieved at a current density of 60 mA cm⁻². Furthermore, we observed 99% capacity retention over 100 cycles and 75% capacity retention over 500 charge/discharge cycles. Additionally, we performed a detailed Density Functional Theory (DFT) analysis of MMV. This study underscores the importance of inhibiting dimer formation in viologen derivatives and positions MMV as a promising negolyte surpassing DMV.

中文翻译：

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单甲基紫精：一种有前途的碱性水氧化还原液流电池阳极电解液


水系氧化还原液流电池（ARFB）因其相对较低的成本和丰富的原材料而成为大规模储能系统的可持续选择。然而，迫切需要通过解决氧化还原活性物质稳定性低和溶解度差等限制来提高其功率密度和能源效率。在这项研究中，我们对一种名为MMV（1-甲基-4,4'-联吡啶碘化物）的不对称紫罗碱基电解液进行了系统分析，并对其与N , N'-二甲基-4,4'-联吡啶进行了详细的比较研究二碘化物（二甲基紫精（DMV））。经过广泛的电化学表征，我们构建了一种碱性 MMV 电池，与较高浓度 (0.8 M) 的铁氰化钾正电解质配对，产生 1.25 V 的电池电压，几乎相当于钒 RFB 的电池电压。值得注意的是，在60 mA cm ^-2的电流密度下实现了97%库仑效率（CE）和71%能量效率（EE）的长期循环。此外，我们观察到 100 次循环后容量保持率为 99%，500 次充电/放电循环后容量保持率为 75%。此外，我们对 MMV 进行了详细的密度泛函理论 (DFT) 分析。这项研究强调了抑制紫精衍生物中二聚体形成的重要性，并将 MMV 定位为超越 DMV 的有前途的溶剂。