Quantifying Hydrogen Chemical Diffusivity in NdNiO₃ Thin Films through <i>Operando</i> Multimodal Measurements

Nickelate oxides show unique properties that make them highly applicable in electrocatalysis, neuromorphic computing, and superconductors. Proton insertion, which effectively tunes their properties, is critical in advancing these applications. Its dynamics is governed by protonation kinetics, mainly controlled by hydrogen chemical diffusivity in nickelates. However, its precise quantification remains a significant knowledge gap, with reported values showing substantial discrepancies and a lack of comprehensive, rigorous methods. In this study, we propose a new quantitative approach that combines <i>operando</i> multimodal measurements. We provide the precise quantification of hydrogen chemical diffusivity in NdNiO₃ (NNO), a prototypical nickelate, using rigorous kinetic modeling and cross-validation across multiple data dimensions. Our results reveal that proton mobility in NNO is inherently limited, challenging the assumption of its rapid transport in nickelates. This finding is critical for optimizing proton-based devices and paves the way for further understandings ion dynamics in correlated oxides.