For steady electroconversion to value-added chemical products with high efficiency, electrocatalyst reconstruction during electrochemical reactions is a critical issue in catalyst design strategies. Here, we report a reconstruction-immunized catalyst system in which Cu nanoparticles are protected by a quasi-graphitic C shell. This C shell epitaxially grew on Cu with quasi-graphitic bonding via a gas–solid reaction governed by the CO (g) - CO2 (g) - C (s) equilibrium. The quasi-graphitic C shell-coated Cu was stable during the CO2 reduction reaction and provided a platform for rational material design. C2+ product selectivity could be additionally improved by doping p-block elements. These elements modulated the electronic structure of the Cu surface and its binding properties, which can affect the intermediate binding and CO dimerization barrier. B-modified Cu attained a 68.1% Faradaic efficiency for C2H4 at −0.55 V (vs RHE) and a C2H4 cathodic power conversion efficiency of 44.0%. In the case of N-modified Cu, an improved C2+ selectivity of 82.3% at a partial current density of 329.2 mA/cm2 was acquired. Quasi-graphitic C shells, which enable surface stabilization and inner element doping, can realize stable CO2-to-C2H4 conversion over 180 h and allow practical application of electrocatalysts for renewable energy conversion.

With the combination of first principle calculations and thermodynamics, a predictive fabrication to modify structure and phase was developed.

Controlled phase conversion in polymorphic transition metal dichalcogenides (TMDs) provides a new synthetic route for realizing tunable nanomaterials. Most conversion methods from the stable 2H to metastable 1T phase are limited to kinetically slow cation insertion into atomically thin layered TMDs for charge transfer from intercalated ions. Here, we report that anion extraction by the selective reaction between carbon monoxide (CO) and chalcogen atoms enables predictive and scalable TMD polymorph control. Sulfur vacancy, induced by anion extraction, is a key factor in molybdenum disulfide (MoS2) polymorph conversion without cation insertion. Thermodynamic MoS2–CO–CO2 ternary phase diagram offers a processing window for efficient sulfur vacancy formation with precisely controlled MoS2 structures from single layer to multilayer. To utilize our efficient phase conversion, we synthesize vertically stacked 1T-MoS2 layers in carbon nanofibers, which exhibit highly efficient hydrogen evolution reaction catalytic activity. Anion extraction induces the polymorph conversion of tungsten disulfide (WS2) from 2H to 1T. This reveals that our method can be utilized as a general polymorph control platform. The versatility of the gas–solid reaction-based polymorphic control will enable the engineering of metastable phases in 2D TMDs for further applications.

Oxide-based memristive devices have recently been proposed for various applications, such as next-generation memory and neuromorphic devices. Microstructural alterations depending on the oxygen ion concentration, such as the formation of conductive filaments and interface reactions, have been posited as the operating mechanism. Accordingly, it is important to explore the role of oxygen ion mobility in the behavior of memristive devices. In this study, memristive devices fabricated with brownmillerite SrFeO2.5 in the (111) and (001) orientations were studied via high-resolution transmission electron microscopy and in situ current–voltage measurements. The resistance of the devices was changed by a reversible topotactic phase change between the insulating brownmillerite SrFeO2.5 and the conductive perovskite SrFeO3−δ. Importantly, the oxygen vacancy channel was designed so that the phase change occurred across the electrodes in (111), where the channel was directly connected to both electrodes, whereas in (001) the channel is ordered along the in-plane direction and a phase change occurs only near the electrode. This work provides direct evidence of a brownmillerite-based mechanism of resistance change and a better understanding of routes to performance improvement.

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