Asymmetric electron occupation of transition metals for the oxygen evolution reaction via a ligand–metal synergistic strategy

Asymmetric electron occupation of transition metals for the oxygen evolution reaction via a ligand–metal synergistic strategy

Phys. Chem. Chem. Phys. 26, 27209-27215 (2024).

Pai Wang, Kunyu Li, Tongwei Wu, Wei Ji, and Yanning Zhang

The performance of two-dimensional transition-metal (oxy)hydroxides (TMOOHs) for the electrocatalytic oxygen evolution reaction (OER), as well as their large-scale practical applications, are severely limited by the sluggish kinetics of the four-electron OER process. Herein, using a symmetry-breaking strategy, we simulated a complex catalyst composed of a single Co atom and a 1,10-phenanthroline (phen) ligand on CoOOH through density functional theory studies, which exhibits excellent OER performance. The active site Co undergoes a valence oscillation between +2, +3 and even high valence +4 oxidation states during the catalytic process, resulting from the distorted coordination effect after the ligand modification. The induced asymmetry in the electronic states of surrounding nitrogen and oxygen atoms modulates the eg occupation of Co-3d orbitals, which should be of benefit to reduce the overpotential in the OER process. By studying similar catalytic systems, the prominent role of ligands in creating asymmetric electronic structures and in modulating the valence of the active site and the OER performance was reconfirmed. This study provides a new dimension for optimizing the electrocatalytic performance of various TM–ligand complexes.

Distance-dependent magnetization modulation induced by inter-superatomic interactions in Cr-doped Au6Te12Se8 dimers

Distance-dependent magnetization modulation induced by inter-superatomic interactions in Cr-doped Au6Te12Se8 dimers

Chin. Phys. B 33, 127502 (2024)

Yurou Guan (官雨柔), Nanshu Liu(刘南舒), Cong Wang(王聪), Fei Pang(庞斐), Zhihai Cheng(程志海), and Wei Ji(季威)*

Individual superatoms were assembled into more complicated nanostructures for diversify their physical properties. Magnetism of assembled superatoms remains, however, ambiguous, particularly in terms of its distance dependence. Here, we report density functional theory calculations on the distance-dependent magnetism of transition metal embedded Au6Te8Se12 (ATS) superatomic dimers. Among the four considered transition metals, which include V, Cr, Mn and Fe, the Cr-embedded Au6Te12Se8 (Cr@ATS) is identified as the most suitable for exploring the inter-superatomic distance-dependent magnetism. We thus focused on Cr@ATS superatomic dimers and found an inter-superatomic magnetization-distance oscillation where three transitions occur for magnetic ordering and/or anisotropy at different inter-superatomic distances. As the inter-superatomic distance elongates, a ferromagnetism (FM)-to-antiferromagnetic (AFM) transition and a sequential AFM-to-FM transition occur, ascribed to competitions among Pauli repulsion and kinetic-energy-gains in formed inter-superatomic Cr-Au-Au-Cr covalent bonds and Te-Te quasi-covalent bonds. For the third transition, in-plane electronic hybridization contributes to the stabilization of the AFM configuration. This work unveils two mechanisms for tuning magnetism through non-covalent interactions and provides a strategy for manipulating magnetism in superatomic assemblies.

Coexistence of ferroelectricity and antiferroelectricity in 2D van der Waals multiferroic

Coexistence of ferroelectricity and antiferroelectricity in 2D van der Waals multiferroic

Yangliu Wu, Zhaozhuo Zeng, Haipeng Lu, Xiaocang Han, Chendi Yang, Nanshu Liu, Xiaoxu Zhao, Liang Qiao, Wei Ji*, Renchao Che, Longjiang Deng*, Peng Yan* and Bo Peng*

Multiferroic materials have been intensively pursued to achieve the mutual control of electric and magnetic properties. The breakthrough progress in 2D magnets and ferroelectrics encourages the exploration of low-dimensional multiferroics, which holds the promise of understanding inscrutable magnetoelectric coupling and inventing advanced spintronic devices. However, confirming ferroelectricity with optical techniques is challenging in 2D materials, particularly in conjunction with antiferromagnetic orders in single- and few-layer multiferroics. Here, we report the discovery of 2D vdW multiferroic with out-of plane ferroelectric polarization in trilayer NiI2 device, as revealed by scanning reflective magnetic circular dichroism microscopy and ferroelectric hysteresis loops. The evolution between ferroelectric and antiferroelectric phases has been unambiguously observed. Moreover, the magnetoelectric interaction is directly probed by magnetic control of the multiferroic domain switching. This work opens up opportunities for exploring new multiferroic orders and multiferroic physics at the limit of single or few atomic layers, and for creating advanced magnetoelectronic devices.

Real-space topology-engineering of skyrmionic spin textures in a van der Waals ferromagnet Fe3GaTe2

Real-space topology-engineering of skyrmionic spin textures in a van der Waals ferromagnet Fe3GaTe2

Nano Letters 24, 13094–13102 (2024) / arXiv:2407.16924

Shuo Mi, Jianfeng Guo, Guojing Hu, Guangcheng Wang, Songyang Li, Zizhao Gong, Shuaizhao Jin, Rui Xu, Fei Pang, Wei Ji, Weiqiang Yu, Xiaolei Wang*, Xueyun Wang*, Haitao Yang*, Zhihai Cheng*

Realizing magnetic skyrmions in two-dimensional (2D) van der Waals (vdW) ferromagnets offers unparalleled prospects for future spintronic applications. The room-temperature ferromagnet Fe3GaTe2 provides an ideal platform for tailoring these magnetic solitons. Here, skyrmions of distinct topological charges are artificially introduced and spatially engineered using magnetic force microscopy (MFM). The skyrmion lattice is realized by specific field-cooling process, and can be further controllably erased and painted via delicate manipulation of tip stray field. The skyrmion lattice with opposite topological charges (S = +1 or -1) can be tailored at the target regions to form topological skyrmion junctions (TSJs) with specific configurations. The delicate interplay of TSJs and spin-polarized device current were finally investigated via the in-situ transport measurements, alongside the topological stability of TSJs. Our results demonstrate that Fe3GaTe2 not only serves as a potential building block for room-temperature skyrmion-based spintronic devices, but also presents promising prospects for Fe3GaTe2-based heterostructures with the engineered topological spin textures.

Layer-by-layer growth of bilayer graphene single-crystals enabled by proximity catalytic activity

Layer-by-layer growth of bilayer graphene single-crystals enabled by proximity catalytic activity

NanoToday 59, 102482 (2024)

Zhihong Zhang, Linwei Zhou, Zhaoxi Chen* , Antonín Jaroš, Miroslav Kolíbal, Petr Bábor, Quanzhen Zhang, Changlin Yan, Ruixi Qiao, Qing Zhang, Teng Zhang, Wei Wei, Yi Cui, Jingsi Qiao, Liwei Liu, Lihong Bao, Haitao Yang, Zhihai Cheng, Yeliang Wang, Enge Wang, Zhi Liu, Marc Willinger, Hong-Jun Gao, Kaihui Liu*, Wei Ji*, and Zhu-Jun Wang*

Direct growth of large-area vertically stacked two-dimensional (2D) van der Waal (vdW) materials is a prerequisite for their high-end applications in integrated electronics, optoelectronics and photovoltaics. Currently, centimetre- to even metre-scale monolayers of single-crystal graphene (MLG) and hexagonal boron nitride (h-BN) have been achieved by epitaxial growth on various single-crystalline substrates. However, in principle, this success in monolayer epitaxy seems extremely difficult to be replicated to bi- or few-layer growth, as the full coverage of the first layer was believed to terminate the reactivity of those adopting catalytic metal surfaces. Here, we report an exceptional layer-by-layer chemical vapour deposition (CVD) growth of large size bi-layer graphene single-crystals, enabled by proximity catalytic activity from platinum (Pt) surfaces to the outermost graphene layers. In-situ growth and real-time surveillance experiments, under well-controlled environments, unambiguously verify that the growth does follow the layer-by-layer mode on open surfaces of MLG/Pt(111). First-principles calculations indicate that the transmittal of catalytic activity is allowed by an appreciable electronic hybridisation between graphene overlayers and Pt surfaces, enabling catalytic dissociation of hydrocarbons and subsequently direct graphitisation of their radicals on the outermost sp2 carbon surface. This proximity catalytic activity is also proven to be robust for tube-furnace CVD in fabricating single-crystalline graphene bi-, tri- and tetra-layers, as well as h-BN few-layers. Our findings offer an exceptional strategy for potential controllable, layer-by-layer and wafer-scale growth of vertically stacked few-layered 2D single crystals.

Correlated electrons in the flat band in the charge density wave state of 4Hb−TaSexS2−x

Correlated electrons in the flat band in the charge density wave state of 4Hb−TaSexS2−x

Yanyan Geng#, Jianfeng Guo#, Fanyu Meng#, Manyu Wang, Shuo Mi, Li Huang, Rui Xu, Fei Pang, Kai Liu, Shancai Wang, Hong-Jun Gao, Weichang Zhou, Wei Ji*, Hechang Lei*, and Zhihai Cheng*

Many intriguing quantum states of matter, such as unconventional superconductivity, magnetic phases, and fractional quantum Hall physics, emerge from the spatially correlated localized electrons in the flat bands of solid materials. By using scanning tunneling microscopy and spectroscopy (STM/STS), we report on the real-space investigation of correlated electrons in the flat band of superlattice 4⁢𝐻𝑏⁡−TaS⁢e𝑥⁢S2−𝑥. In contrast with the pristine 4⁢𝐻𝑏⁡−Ta⁢S2, the selenium (Se) substitutions significantly affect the interfacial transfer of correlated electrons between the charge density wave (CDW) states of 1⁢𝑇- and 1⁢𝐻⁡−Ta⁢S2 layers and contribute the real-space fractional electron-filling configurations with the distributed electron-filled and void Star of David (SoD) clusters of the 1⁢𝑇 layer. The site-specific STS spectra directly reveal their respective prominent spectra weight above 𝐸F and symmetric Mott-like spectra. In addition, the spatial distributions of these electron-filled SoDs in the 1⁢𝑇 layer of 4⁢𝐻𝑏⁡−TaS⁢e0.7⁢S1.3 demonstrate different local short-range order, clearly indicating the complex neighboring interactions among the localized electrons in the flat band of the 1⁢𝑇 layer. Our results not only provide in-depth insight into correlated electrons in the flat CDW band but also provide a simple platform to manipulate the electron-correlation-related quantum states.