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It has been brought to our attention that a mistake exists in the author list. The author “Johnson Goh” in the original article should be “Kuan Eng Johnson Goh”. His primary corresponding email is kejgoh@yahoo.com.

We present a combined experimental and theoretical study of monolayer vanadium ditelluride, VTe2, grown on highly oriented pyrolytic graphite by molecular-beam epitaxy. Using various in situ microscopic and spectroscopic techniques, including scanning tunneling microscopy/spectroscopy, synchrotron X-ray and angle-resolved photoemission, and X-ray absorption, together with theoretical analysis by density functional theory calculations, we demonstrate direct evidence of the metallic 1T phase and 3d1 electronic configuration in monolayer VTe2 that also features a (4 × 4) charge density wave order at low temperatures. In contrast to previous theoretical predictions, our element-specific characterization by X-ray magnetic circular dichroism rules out a ferromagnetic order intrinsic to the monolayer. Our findings provide essential knowledge necessary for understanding this interesting yet less explored metallic monolayer in the emerging family of van der Waals magnets.

An atomically dispersed structure is attractive for electrochemically converting carbon dioxide (CO 2 ) to fuels and feedstock due to its unique properties and activity. Most single-atom electrocatalysts are reported to reduce CO 2 to carbon monoxide (CO). Herein, we develop atomically dispersed indium (In) on a nitrogen-doped carbon skeleton (In-N-C) as an efficient catalyst to produce formic acid/formate in aqueous media, reaching a turnover frequency as high as 26771 h -1 at -0.99 V relative to a reversible hydrogen electrode (RHE). Electrochemical measurements show that trace amounts of In loaded on the carbon matrix significantly improve the electrocatalytic behavior for the CO 2 reduction reaction, outperforming conventional metallic In catalysts. Further experiments and density functional theory (DFT) calculations reveal that the formation of intermediate *OCHO on isolated In sites plays a pivotal role in the efficiency of the CO 2 -to-formate process, which has a lower energy barrier than that on metallic In.

Epitaxial Fe 3 O 4 thin films grown on single crystal MgO(001) present well-defined model systems to study fundamental multivalent ion diffusion and associated phase transition processes in transition-metal-oxide-based cathodes. In this work, we show at an atomic scale the Mg 2+ diffusion pathways, kinetics, and reaction products at the Fe 3 O 4 /MgO heterostructures under different oxygen partial pressures but with the same thermal annealing conditions. Combining microscopic, optical, and spectroscopic techniques, we demonstrate that an oxygen-rich environment promotes facile Mg 2+ incorporation into the Fe 2+ sites, leading to the formation of Mg 1- x Fe 2+ x O 4 spinel structures, where the corresponding portion of the Fe 2+ ions are oxidized to Fe 3+ . Conversely, annealing in vacuum results in the formation of a thin interfacial rocksalt layer (Mg 1- y Fe y O), which serves as a blocking layer leading to significantly reduced Mg 2+ diffusion to the bulk Fe 3 O 4 . The observed changes in transport and optical properties as a result of Mg diffusion are interpreted in light of the electronic structures determined by X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. Our results reveal the critical role of available anions in governing cation diffusion in the spinel structures and the need to prevent formation of unwanted reaction intermediates for the promotion of facile cation diffusion.

Enhancing catalytic activity by decorating noble metals in catalysts provides an opportunity for promoting the electrocatalytic hydrogen evolution reaction (HER) application. However, there are few systematic studies on regulating the structures of noble metals in catalytic materials and investigating their influence on HER. Herein, Pt catalysts with different structures including single atoms (SAs), clusters, and nanoparticles well-controllably anchored on VS 2 nanosheets through a cost-effective optothermal method are reported, and their HER performance is studied. The most efficient Pt-decorated VS 2 catalyst (with both Pt SAs and clusters) delivers an overpotential of 77 mV at 10 mA cm -2 , close to that of Pt/C (48 mV). However, the optimal mass activity of Pt (normalizing to Pt content) is obtained from only SA Pt-decorated VS 2 ( i.e. , 22.88 A mg Pt -1 at 200 mV) and is 12 times greater than that of the Pt/C (1.87 A mg Pt -1 ), attributed to the greatly enhanced Pt utilization. Additionally, the theoretical simulations reveal that Pt SA decoration makes the adsorption free energy of H* closer to the thermoneutral value and improves the charge-transfer kinetics, significantly enhancing HER activity. This work offers a pathway to prepare the desired catalyst based on synergy of Pt structures and VS 2 and reveals the intrinsic mechanism for enhancing catalytic activity, which is important for HER applications.

We present a combined experimental and theoretical study of monolayer vanadium ditelluride, VTe 2 , grown on highly oriented pyrolytic graphite by molecular-beam epitaxy. Using various in situ microscopic and spectroscopic techniques, including scanning tunneling microscopy/spectroscopy, synchrotron X-ray and angle-resolved photoemission, and X-ray absorption, together with theoretical analysis by density functional theory calculations, we demonstrate direct evidence of the metallic 1T phase and 3d 1 electronic configuration in monolayer VTe 2 that also features a (4 × 4) charge density wave order at low temperatures. In contrast to previous theoretical predictions, our element-specific characterization by X-ray magnetic circular dichroism rules out a ferromagnetic order intrinsic to the monolayer. Our findings provide essential knowledge necessary for understanding this interesting yet less explored metallic monolayer in the emerging family of van der Waals magnets.

Electrolyte gating is widely used to induce large carrier density modulation on solid surfaces to explore various properties. Most of past works have attributed the charge modulation to electrostatic field effect. However, some recent reports have argued that the electrolyte gating effect in VO 2 , TiO 2 , and SrTiO 3 originated from field-induced oxygen vacancy formation. This gives rise to a controversy about the gating mechanism, and it is therefore vital to reveal the relationship between the role of electrolyte gating and the intrinsic properties of materials. Here, we report entirely different mechanisms of electrolyte gating on two high-T c cuprates, NdBa 2 Cu 3 O 7-δ (NBCO) and Pr 2-x Ce x CuO 4 (PCCO), with different crystal structures. We show that field-induced oxygen vacancy formation in CuO chains of NBCO plays the dominant role, while it is mainly an electrostatic field effect in the case of PCCO. The possible reason is that NBCO has mobile oxygen in CuO chains, while PCCO does not. Our study helps clarify the controversy relating to the mechanism of electrolyte gating, leading to a better understanding of the role of oxygen electro migration which is very material specific.