High-Voltage Symmetric Nonaqueous Redox Flow Battery Based on Modularly Tunable [Ru₂M(μ₃-O)(CH₃CO₂)₆(py)₃] (M = Ru, Mn, Co, Ni, Zn) Cluster Compounds with Multielectron Storage Capability

Redox flow batteries (RFBs) provide an attractive solution for large-scale energy buffering and storage. This report describes the development of nonaqueous RFBs based on trimetallic coordination cluster compounds: [Ru2M(μ3-O)(CH3CO2)6(py)3] (M = Ru, Mn, Co, Ni, Zn). The all-ruthenium complex exhibited stable battery cycles in anolyte–catholyte symmetric operation, with rarely observed multielectron storage in a single molecule. Moreover, the complex holds modularly tunable synthetic handles for systematic improvements in solubility and redox potentials. An optimized battery stack containing [Ru3(μ3-O)(CH3CO2)6(py)3]+ anolyte and [Ru2Co(μ3-O)(CH3CO2)6(py)3] catholyte yielded stable cycles with a discharge voltage of 2.4 V, comparable to the state-of-the-art nonaqueous RFBs. Explanation for the exceptional stability of the charged states and prediction of systematic tunability of the redox potentials of the cluster compounds were assisted by DFT calculations.