Molecular O2 Dimers and Lattice Instability in a Perovskite Electrocatalyst

Structural degradation of oxide electrodes during electrocatalytic oxygen evolution reaction (OER) is a major challenge in water electrolysis. Although the OER is known to induce changes in the surface layer, little is understood about its effect on the bulk of the electrocatalyst and the overall phase stability. Here, we show that under OER conditions a highly active SrCoO3-x electrocatalyst develops bulk lattice instability, which results in the formation of molecular O2 dimers in the bulk and nanoscale amorphization induced via chemo-mechanical coupling. Using high-resolution resonant inelastic X-ray scattering (RIXS) and first principles calculations, we unveil the potential-dependent evolution of lattice oxygen inside the perovskite and demonstrate that O2 dimers are stable in a densely packed crystal lattice, thus challenging the assumption that O2 dimers require sufficient inter-atomic spacing. We also show that SrCoO3-x develops unusual amorphous bands under intercalation-induced stress that indicates the lattice requires a remarkably low energy to undergo the order-disorder transition. As a result, we propose the amorphization energy as a descriptor of the electrocatalyst stability that can be calculated from the first principles. Our study demonstrates that extreme oxidation of electrocatalysts under OER can intrinsically destabilize the lattice and result in bulk anion redox and disorder, suggesting why some oxide materials are unstable and develop a thick amorphous layer under water electrolysis conditions.