Proton-Induced Disproportionation of Jahn–Teller-Active Transition-Metal Ions in Oxides Due to Electronically Driven Lattice Instability

The interfacial chemical reactivity of Jahn–Teller-active transition-metal oxides remains an enigmatic area, often leading to uncontrollable phase transformations in the oxide-based technological applications. In particular, the higher tendency of unwanted transition-metal-ion dissolution and side-reactions in Jahn–Teller-active oxides is accompanied by performance degradation in many electrochemical systems, for example, lithium-ion batteries. We show here that the fundamental electronic structure instability that leads to Jahn–Teller (lattice) distortion in an octahedral ligand field is the active chemical driving force for the spontaneous disproportionation, phase transformation, and metal-ion dissolution in transition-metal oxides upon exposure to protons. On the basis of electronic structure analyses and 18O isotope labeling, we present a mechanism comprising a coupled acid–base/redox reaction that leads to a proton-induced disproportionation of Jahn–Teller-active transition-metal ions, as exemplified by the broad classes of respective oxides.