Operando Studies Redirect Spatiotemporal Restructuration of Model Coordinated Oxides in Electrochemical Oxidation

Abstract

Tetrahedral, pyramidal, and octahedral metal-oxygen coordinated ligands are fundamental components in all metal-oxide structures. Understanding the impacts of their spatiotemporal behaviors during electrochemical oxidation is crucial for diverse applications, yet remains unsolved due to challenges in designing model oxides and conducting operando characterizations. Herein, combining a suite of advanced operando characterizations and systematic computations, a link between oxygen-evolving performance and operational structural properties is established on model oxides. Compared with tetrahedral and octahedral structures, pyramidal structure is more susceptible to OH^- attack due to its pristine unsaturated and asymmetric features and constant single-electron occupancy on the active z² orbital during reaction, leading to surface-to-bulk restructuration into active amorphous high-valence CoOOH_x with edge-sharing configurations. This is accompanied by ion leaching to create nanoscale space, following a leaching tendency of Sr²⁺ > Ba²⁺ > La³⁺ > Y³⁺. Operando soft X-ray absorption spectroscopy demonstrates a harder non-uniform dehydrogenation process over time (Co³⁺OOH → Co^3+/4+OOH_x → Co⁴⁺OO) because of the enhanced CoO covalency with higher energy barriers. Lattice oxygen participates in active CoOOH_x formation but sacrifices stability. To address this activity-stability trade-off, an ion-tuning strategy is proposed to simultaneously enhance both activity and stability in electrode and device.