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.

We provide a simple and systematic computational model to study ion channel permeability using density functional theory. While existing permeability models with a hard-wall steric hindrance factor work reasonably well for large ions, they severely inhibit the permeation of small ions through channel pores.Here, by introducing a steric hindrance factor that allows pore expansion due to intrinsically soft ion transfer channel walls, the new permeability model accurately describes the effect of steric hindrance stemming from the soft and flexible ion channel wall. Most importantly, the soft-wall ion transfer channel model works for a wide range of ionic radii from fluoride to gluconate. In addition, we show that strong local electrostatic interaction between densely charged ions such as fluoride and bicarbonate and ion channels with ion binding sites significantly promotes the permeation processes. K E Y W O R D S density functional theory (DFT), ion channel permeability, soft-wall ion transfer channel (SWITCH)

Reversible conversion over multimillion times in bond types between metavalent and covalent bonds becomes one of the most promising bases for universal memory. As the conversions have been found in metastable states, an extended category of crystal structures from stable states via redistribution of vacancies, research on kinetic behavior of the vacancies is highly in demand. However, it remains lacking due to difficulties with experimental analysis. Herein, the direct observation of the evolution of chemical states of vacancies clarifies the behavior by combining analysis on charge density distribution, electrical conductivity, and crystal structures. Site-switching of vacancies of Sb 2 Te 3 gradually occurs with diverged energy barriers owing to their own activation code: the accumulation of vacancies triggers spontaneous gliding along atomic planes to relieve electrostatic repulsion. Studies on the behavior can be further applied to multiphase superlattices composed of Sb 2 Te 3 (2D) and GeTe (3D) sublayers, which represent superior memory performances, but their operating mechanisms were still under debate due to their complexity. The site-switching is favorable (suppressed) when Te−Te bonds are formed as physisorption (chemisorption) over the interface between Sb 2 Te 3 (2D) and GeTe (3D) sublayers driven by configurational entropic gain (electrostatic enthalpic loss). Depending on the type of interfaces between sublayers, phases of the superlattices are classified into metastable and stable states, where the conversion could only be achieved in the metastable state. From this comprehensive understanding on the operating mechanism via kinetic behaviors of vacancies and the metastability, further studies toward vacancy engineering are expected in versatile materials.