Operando Exploration of CoAl-LDH: Transformations Driving Alkaline Oxygen Evolution Reaction.

This work reports a comprehensive study on the morphology, composition, and electronic structure of CoAl layered double hydroxide (CoAl-LDH) during the oxygen evolution reaction (OER). To capture electrochemically induced transformations, operando spectroscopic and microscopic methods are combined. The complementary data provided by operando near-edge X-ray absorption fine structure (NEXAFS), supported by density functional theory (DFT) calculations, and electrochemical atomic force microscopy (AFM), reveal that under OER conditions, CoAl-LDH is fragmented into smaller particles due to Al leaching. This process forms a "resting" phase with an average Co oxidation state of 2.5+, which readily transforms into the OER-active β-CoOOH phase upon further potential increase. This work exemplifies how operando methods enable precise tracking of oxidation state changes, element dissolution, and structural transformations at the nanoscale while the electrocatalyst is active. This approach contrasts with conventional pre- and post-mortem characterization, which would instead suggest CoO formation. These findings extend beyond the specific example of CoAl-LDH, emphasizing the crucial importance of selective cation leaching, recrystallization, and morphological restructuring, since these processes play a key role not only in designing advanced multi-element materials but also in understanding the complex nanoscale mechanisms that govern the activation and durability of practical electrocatalysts.