Magnetic Insights Into Heterogeneous and Nonequilibrium Electrochemical Reactions

Electrochemical energy systems are governed by interfacial reactions that are spatially heterogeneous and far from equilibrium, causing deviations from ideal behavior and unexpected phenomena. Despite significant advances, conventional characterization techniques remain limited in resolving these complex mechanisms, guiding materials design, and optimizing performance. A key missing link is a diagnostic platform that is sensitive to local electronic- and spin-state evolution, nondestructive, sufficiently penetrative, and capable of time-resolved tracking under realistic operating conditions. In this Perspective, we highlight magnetic characterization as a spin-sensitive approach for deciphering heterogeneous and nonequilibrium electrochemical reactions. By monitoring magnetization, magnetic susceptibility, and resonance signals under operando or in situ conditions, magnetic characterization correlates magnetic signatures and electronic-configuration changes with mechanisms that remain difficult to access. We summarize recent advances in applying magnetic techniques to representative processes, including interfacial space-charge storage, metal deposition pathways, lattice-oxygen anionic redox reactions, and transient radical/reactive-intermediate chemistry. Finally, we outline future directions, including high-sensitivity operando magnetometry, standardized operando platforms, and synergistic integration with spectroscopy, microscopy, and data-driven methodologies, positioning magnetic characterization techniques as a practical toolkit for elucidating heterogeneous, nonequilibrium electrochemical interfacial reactions and informing the design of next-generation batteries and electrocatalysts.