Guangwen Zhou

Metal oxidation is traditionally described as a dichotomy: oxide scales grow either outward via cation diffusion or inward via anion diffusion, with the dominant pathway determined by the prevailing point defects in the oxide lattice. Here, we demonstrate that these two modes are not mutually exclusive but intrinsically coupled within a single oxidation process. Using in situ environmental transmission electron microscopy to monitor the oxidation of copper—a canonical cationic system—we directly visualize simultaneous oxide propagation at both the O ₂ /Cu ₂ O surface interface and the buried Cu ₂ O/Cu interface. Complementary simulations reveal the mechanistic origin of this behavior. Outward cation transport during surface oxide growth injects a sustained flux of vacancies into the underlying metal lattice, which facilitates inward oxygen incorporation and drives oxide growth at the buried interface. This vacancy-mediated feedback couples cationic and anionic transport process, providing a unified framework in which surface cationic growth directly enables inward anionic-driven growth. By identifying vacancy injection as a key mediator of interfacial mass transport, this work provides a mechanistic basis for predicting oxidation kinetics and defect-regulated solid-state transformation pathways in reactive environments.

The atomistic pathways linking oxygen adsorption, surface reconstruction, and oxide nucleation during metal oxidation remain incompletely understood. Here, we investigate the initial oxidation of Cu(111) using a correlative low-energy electron microscopy (LEEM) and scanning tunneling microscopy (STM) approach that bridges mesoscale surface evolution with atomic-scale structural characterization. In situ LEEM reveals that oxidation initiates preferentially at step edges and subsequently propagates across terraces through the growth and coalescence of oxygen-induced domains. Increasing temperature significantly accelerates oxidation kinetics, suppresses terrace nucleation, and promotes dynamic surface reconstruction. Complementary STM observations directly visualize the nucleation and lateral growth of Cu–O structures from step edges and reveal the formation of reconstructed oxide terraces, Cu–O islands, and locally ordered oxide domains. Fourier-transform analysis indicates that the oxidized surface is dominated by short-range ordered Cu–O precursor phases rather than long-range ordered oxide structures. Together, these results establish a temperature-dependent oxidation mechanism governed by step-edge-mediated oxygen incorporation, surface diffusion-driven domain growth, and dynamic surface reconstruction. The findings provide direct multiscale insight into the early stages of Cu(111) oxidation and the fundamental processes controlling oxide nucleation and growth on metal surfaces.

Autoencoder-transformer model applicable to both simulated and experimental XAS spectra is developed to predict the oxidation state of copper.

Chemical segregation governs the structural evolution and properties of nanoalloys and, under vacuum or reducing conditions, typically leads to core–shell structures that minimize surface free energy. Here, we show that surface oxidation fundamentally alters this behavior in Cu–Au nanoalloys by suppressing conventional surface segregation and driving twin‐boundary (TB)‐mediated chemical separation within the particle interior. Combining in situ electron microscopy, ambient‐pressure X‐ray photoelectron spectroscopy, and density functional theory, we reveal that oxidation redirects Au transport from the surface to internal TBs through uphill diffusion from Au‐poor to Au‐rich regions, producing alternating Au‐rich and Cu‐rich lamellae with local Au enrichment of up to ∼50 at.%. This behavior is driven by the negative Cu–Au mixing enthalpy, which favors heteroatomic bonding, while the CuO _x overlayer inhibits Au surface segregation that would otherwise dominate. Consequently, surface oxidation acts as a chemical pump, redirecting atomic flux into the particle interior, where defect‐mediated segregation lowers the free energy by maximizing Cu–Au bonding. These findings demonstrate how surface chemistry, alloy thermodynamics, and lattice defects collectively govern mass transport and internal chemical patterning, providing atomistic insight into the structural evolution and stability of nanoalloys under reactive environments.

Noble metals such as platinum and gold are widely regarded as resistant to oxidation under ambient conditions. We show that interfacing these metals with a reducible oxide alters their redox behavior through dynamic metal–support interactions. Using in situ environmental transmission electron microscopy, we visualize reversible room‐temperature redox cycling of Pt and Au nanoparticles on CeO ₂ under alternating O ₂ and vacuum. Oxygen vacancies in the partially reduced support dissociate O ₂ into reactive atomic oxygen, which spills over to oxidize the supported metal, driving complete conversion of Pt to crystalline Pt ₃ O ₄ , and the formation of ordered oxide species on Au. For Pt/CeO ₂ , redox cycling also induces a reversible wetting–dewetting restructuring in which oxidation promotes dewetting into three‐dimensional oxide islands, whereas reduction drives wetting of metallic Pt into atomically thin rafts, progressively increasing metal dispersion. In contrast, Au/CeO ₂ exhibits self‐limiting surface oxidation, highlighting the role of metal identity in governing restructuring pathways. Density functional theory modeling shows that this process is sustained by a Cabrera–Mott‐type field‐assisted oxidation mechanism enabled by the CeO ₂ support. These results establish reducible oxides as active redox partners rather than passive supports, providing a mechanistic framework for designing low‐temperature oxidation catalysts through support‐driven dynamic chemistry.

Calcium-ion batteries (CIBs) are promising for next-generation energy storage systems. However, many reported Ca-ion storage mechanisms lack direct structural evidence, raising concerns that the observed electrochemistry may instead originate from proton insertion. Herein, we investigate the electrochemical cycling of a VOPO4 electrode in an aprotic Ca electrolyte with trace water to clarify the charge storage mechanism. While electrochemistry, elemental analysis, and X-ray absorption spectroscopy seem to support Ca-ion intercalation in the VOPO4 electrode, X-ray diffraction and electron microscopy unequivocally show proton insertion as the predominant charge storage mechanism. The apparent variation of Ca content in the electrode with the state of charge is attributed to the formation and dissolution of Ca-containing precipitates on the surface of VOPO4 particles. Our work demonstrates the propensity of proton participation in the intercalation reaction in Ca-ion batteries and the necessity of structural evidence in understanding reactions in multivalent electrochemical systems.

Iron oxidation is a fundamental chemical transformation underpinning planetary evolution and technologies ranging from steel metallurgy and corrosion to catalysis and magnetic storage. Despite decades of surface-science research elucidating oxidation kinetics and surface dynamics, the atomic-scale transformations occurring beneath the surface during the incipient stages of oxidation have remained largely inaccessible. Here we directly visualize the atomic genesis of iron oxidation using in situ environmental scanning/transmission electron microscopy (ETEM/ESTEM). We reveal that oxidation begins with the nucleation of an epitaxial FeO layer on metallic iron. Once the FeO film reaches a critical thickness, a lattice-template-driven phase transformation is triggered at the buried FeO/Fe interface, rather than at the gas-exposed surface, leading to the formation of the higher-valence oxide phase Fe₃O₄. This interfacial transformation drives a concerted outward flux of iron cations, continuously regenerating a ∼two-monolayer FeO skin atop a thickening Fe₃O₄ underlayer. This process results in a persistent, self-regulating FeO/Fe₃O₄/Fe trilayer architecture that directly contradicts the prevailing assumption that oxidation states monotonically increase toward the gas-solid interface. By identifying this counterintuitive, interface-driven mechanism, our results provide the missing atomic-scale link for understanding oxide stability and phase evolution in reactive environments.