Redox flow batteries (RFBs) are some of the most promising energy storage systems because of their design flexibility; however, their low energy density is a major drawback limiting widespread application. Most conventional approaches to increase the energy density have involved exploiting high-concentration electrolytes. However, this approach results in many technical issues, such as sluggish kinetics. We propose a strategy of boosting the energy density by exploiting a multi-redox phenazine molecule (5,10-dihydro-5,10-dimethyl phenazine [DMPZ]). DMPZ exhibits double-redox activity at −0.15 and 0.61 V versus Ag/Ag⁺ with remarkable kinetics and chemical stability. Coupled with 9-fluorenone (FL), the DMPZ/FL flow cell can provide the highest energy density per mole (≈85 W hr mol⁻¹) ever reported for RFBs. Furthermore, the marked color change of DMPZ enables the state of charge to be precisely visualized. This novel strategy for a multi-redox material can provide a potential pathway toward high-energy-density RFBs.

氧化还原液流电池（RFB）由于其设计灵活性而成为一些最有前途的储能系统。然而，它们的低能量密度是限制广泛应用的主要缺点。增加能量密度的大多数常规方法涉及开发高浓度电解质。但是，这种方法会导致许多技术问题，例如动力学迟缓。我们提出了一种通过利用多氧化还原吩嗪分子（5,10-二氢-5,10-二甲基吩嗪[DMPZ]）来提高能量密度的策略。DMPZ在相对于Ag / Ag ^+的−0.15和0.61 V电压下具有双重氧化还原活性，具有显着的动力学和化学稳定性。结合9-芴酮（FL），DMPZ / FL流通池可以提供最高的每摩尔能量密度（≈85 W hr mol ^-1）曾经报告过RFB。此外，DMPZ显着的颜色变化使电荷状态得以精确可视化。这种用于多氧化还原材料的新颖策略可以提供通往高能量密度RFB的潜在途径。