2026.01.05《Unlocking Full State-of-Charge of Polyoxometalate for High-Energy-Density Redox Flow Batteries via Concerted Proton-Electron Transfer》

全球向可再生能源的加速转型对大规模储能技术提出了现实需求，液流电池（RFBs）因其本征安全性、可扩展性、长循环寿命等特性成为大规模储能应用中最具有前景的解决方案之一。传统RFBs的氧化还原电对主要依赖于单/双电子转移，能量密度长期处于在较低水平。多金属氧酸盐（POMs），特别是Keggin构型（[XM12O40]ⁿ⁻）和Dawson构型（[X2M18O62]ⁿ⁻）团簇，具有超过12个电子的转移能力，是下一代高能量密度RFBs的理想候选材料。但长期以来，POM实际电解液利用率（此处用充电状态SoC表示）却被限制在理论水平的33.3%以下。究其原因，在于未充分认识POM深度还原条件下的氧化还原机理，以及缺乏能够在高SoC下可逆充放电的POM电解质调控策略。

在发表于《Angewandte Chemie International Edition》的研究中，通过协同质子-电子转移（CPET）机理阐明、高质子活性电解质工程以及稳定可逆氧化还原液流电池验证的综合方法，解决了POM电解质无法实现高SoC可逆充放电循环这一长期存在的挑战。具体而言，该研究通过应用Marcus理论、第一性原理密度泛函理论（DFT）计算和从头算分子动力学（AIMD）模拟，建立了[P2W18O62]6−（{P2W18}）团簇的质子耦合电子转移（PCET）框架，证明了{P2W18}团簇的端氧和桥氧位点的质子化通过区域选择性CPET过程稳定了该团簇的还原态钨位点。原位拉曼光谱与原位pH监测进一步证实了{P2W18}氧化还原过程中质子耦合的可逆性。基于这些机理见解的指导，该研究设计了系列高质子活性的H6{P2W18}负极电解液，并开发了逐步充放电协议，以突破{P2W18}在高SoC下稳定性和可逆性差的瓶颈。组装的氧化还原液流电池在H6{P2W18}负极电解液高SoC下表现出优异的循环性能：在0.3M H6{P2W18}负极电解液66.7% SoC下采用直接充放电协议循环600圈（超过1020小时）后放电容量无明显衰减（95.04 Ah L⁻1）；在0.3M H6{P2W18}负极电解液100% SoC下采用逐步充放电协议实现了141.75 Ah L⁻1的优异放电容量；以及在0.5M H6{P2W18}负极电解液100% SoC下实现创纪录的236.03 Ah L⁻1放电容量和239.02 Wh L⁻1能量密度。这项工作通过精准调控质子与电子的协同行为，彻底释放了POM的全部储能潜力，打破了人们对多酸储能应用的固有认知局限，提供了一套从协同质子-电子转移机理阐释到实际应用的完整创新范式，为构建多电子转移高能量密度氧化还原液流电池提供了全新的思路。

 第一作者：中南大学23级博士研究生韩明君；通讯作者：张晨阳教授和李洁教授

The accelerated global transition to renewable energy has put forward a practical demand for large-scale energy storage technologies, and flow batteries (RFBs) have become one of the most promising solutions for large-scale energy storage applications due to their inherent safety, scalability, and long cycle life. The redox charge of traditional RFBs mainly relies on single/double electron transfer, and the energy density remains at a low level for a long time. Polyoxometalates (POMs), especially Keggin ([XM12O40] ⁿ⁻) and Dawson ([X2M18O62] ⁿ⁻) clusters, have the ability to transfer over 12 electrons and are ideal candidate materials for the next generation of high-energy density RFBs. However, for a long time, the actual electrolyte utilization rate of POM (represented by the state of charge SoC) has been limited to below 33.3% of the theoretical level. The reason lies in the insufficient understanding of the redox mechanism under deep reduction conditions of POM, as well as the lack of POM electrolyte regulation strategies that can reversibly charge and discharge at high SoC.

In the study published in Angewandte Chemie International Edition, a comprehensive approach was employed to elucidate the synergistic proton electron transfer (CPET) mechanism, engineering high proton active electrolytes, and validating stable reversible redox flow batteries, addressing the long-standing challenge of POM electrolytes being unable to achieve high SoC reversible charge discharge cycles. Specifically, this study established a proton coupled electron transfer (PCET) framework for the [P2W18O62] 6 − ({P2W18}) cluster by applying Marcus theory, first principles density functional theory (DFT) calculations, and ab initio molecular dynamics (AIMD) simulations. It was demonstrated that the protonation of the terminal and bridging oxygen sites of the {P2W18} cluster stabilized the reduced tungsten sites of the cluster through a region selective CPET process. In situ Raman spectroscopy and pH monitoring further confirmed the reversibility of proton coupling in the oxidation-reduction process of {P2W18}. Based on these mechanistic insights, this study designed a series of high proton activity H6 {P2W18} negative electrode electrolytes and developed a stepwise charge discharge protocol to overcome the bottleneck of poor stability and reversibility of {P2W18} under high SoC. The assembled redox flow battery exhibits excellent cycling performance under high SoC of H6 {P2W18} negative electrode electrolyte: after 600 cycles (over 1020 hours) using a direct charge discharge protocol at 66.7% SoC of 0.3M H6 {P2W18} negative electrode electrolyte, there is no significant decrease in discharge capacity (95.04 Ah L ⁻ 1); An excellent discharge capacity of 141.75 Ah L ⁻ 1 was achieved using a stepwise charge discharge protocol in a 0.3M H6 {P2W18} negative electrode electrolyte with 100% SoC; And achieved a record breaking 236.03 Ah L ⁻ 1 discharge capacity and 239.02 Wh L ⁻ 1 energy density at 100% SoC of 0.5M H6 {P2W18} negative electrode electrolyte. This work precisely regulates the synergistic behavior of protons and electrons, completely unleashing the full energy storage potential of POM, breaking the inherent cognitive limitations of multi acid energy storage applications, and providing a complete innovative model from the explanation of the synergistic proton electron transfer mechanism to practical applications, providing a new idea for building multi electron transfer high-energy density redox flow batteries.

First Author：Mingjun Han；

Corresponding Authors：Chenyang Zhang & Jie Li

Unlocking Full State-of-Charge of Polyoxometalate for High-Energy-Density Redox Flow Batteries via Concerted Proton-Electron Transfer