arXiv subjects

Wencai Ren

Publications and source records attributed to Wencai Ren.

10 recordsLinked to original sources

arXiv2026

Large-scale Integration of Experimental and Computational Data for 2D Materials

The past decade has seen rapid growth in the number of experimentally realized two-dimensional (2D) materials with diverse chemical and physical properties. However, information on their crystal structure, synthesis routes, and measured or predicted properties, remains scattered across thousands of publications. Here we consolidate this fragmented knowledge by establishing X2DB - an open infrastructure that integrates experimental and computational data on 2D materials. Using extensive literature mining and direct community uploads, we identify 370 unique 2D materials that have been realized in monolayer or few-layer form, and link them to their digital counterparts in computational databases, enabling consistent ab initio characterization of their properties across monolayer, bilayer and bulk forms. We describe the structure and content of the database highlighting its support for community uploads, illustrate how it can be used to generate new scientific insight and introduce a hierarchical classification of the known set of 2D materials. Our work provides a foundation for the integration and cross-fertilization of experimental and theoretical knowledge, opening new avenues for data-driven, predictive synthesis of novel 2D materials.

cond-mat.mtrl-sci↗

arXiv2025

The 2D Materials Roadmap

Over the past two decades, 2D materials have rapidly evolved into a diverse and expanding family of material platforms. Many members of this materials class have demonstrated their potential to deliver transformative impact on fundamental research and technological applications across different fields. In this roadmap, we provide an overview of the key aspects of 2D material research and development, spanning synthesis, properties and commercial applications. We specifically present roadmaps for high impact 2D materials, including graphene and its derivatives, transition metal dichalcogenides, MXenes as well as their heterostructures and moiré systems. The discussions are organized into thematic sections covering emerging research areas (e.g., twisted electronics, moiré nano-optoelectronics, polaritronics, quantum photonics, and neuromorphic computing), breakthrough applications in key technologies (e.g., 2D transistors, energy storage, electrocatalysis, filtration and separation, thermal management, flexible electronics, sensing, electromagnetic interference shielding, and composites) and other important topics (computational discovery of novel materials, commercialization and standardization). This roadmap focuses on the current research landscape, future challenges and scientific and technological advances required to address, with the intent to provide useful references for promoting the development of 2D materials.

cond-mat.mtrl-sci↗

arXiv2025

A two-dimensional semiconductor-semimetal drag hybrid

Lateral charge transport of a two-dimensional (2D) electronic system can be much influenced by feeding a current into another closely spaced 2D conductor, known as the Coulomb drag phenomenon -- a powerful probe of electron-electron interactions and collective excitations. Yet the materials compatible for such investigations remain limited to date. Especially, gapped 2D semiconductors with inherently large correlations over a broad gate range have been rarely accessible at low temperatures. Here, we show the emergence of a large drag response (drag resistance $R_{\text{drag}}$ at the order of k$Ω$, with a passive-to-active drag ratio up to $\sim$ 0.6) in a semiconductor-semimetal hybrid, realized in a graphene-MoS$_{2}$ heterostructure isolated by an ultrathin 3 nm hexagonal boron nitride (h-BN) dielectric. We observe a crossover of $T$ to $T^{2}$ dependence of $R_{\text{drag}}$, separated by a characteristic temperature $T_{d} \sim E_{F}/k_{F}d$ ($d$ being the interlayer distance), in echo with the presence of a metal-insulator transition in the semiconducting MoS$_{2}$. Interestingly, the current nanostructure allows the decoupling of intralayer interaction-driven drag response by varying density in one layer with that in the other layer kept constant. A large Wigner-Seitz radius $r_{s}$ ($>$ 10 within the density range of 1 to $4 \times 10^{12}~\mathrm{cm}^{-2}$) in the massive Schrödinger carriers in MoS$_{2}$ is thus identified to dominate the quadratic dependence of total carriers in the drag system, while the massless Dirac carriers in graphene induce negligible drag responses as a function of carrier density. Our findings establish semiconductor-semimetal hybrid as a platform for studying unique interaction physics in Coulomb drag systems.

cond-mat.mes-hall↗

arXiv2022

A Ta-TaS2 monolithic catalyst with robust and metallic interface for superior hydrogen evolution

The use of highly active and robust catalysts is crucial for producing green hydrogen by water electrolysis as we strive to achieve global carbon neutrality. Noble metals like platinum are currently used in industry for the hydrogen evolution reaction (HER), but suffer from scarcity, high price and unsatisfied performance and stability at large current density, restricting their large scale implementations. Here we report the synthesis of a new type of monolithic catalyst (MC) consisting of a metal disulfide (e.g., TaS2) catalyst vertically bonded to a conductive substrate of the same metal by strong covalent bonds. These features give the MC a mechanically robust and electrically near zero resistance interface, leading to an outstanding HER performance including rapid charge transfer and excellent durability, together with a low overpotential of 398 mV to achieve a current density of 2,000 mA cm-2 as required by industry. The Ta TaS2 MC has a negligible performance decay after 200 h operation at large current densities. In light of its unique interface and the various choice of metal elements giving the same structure, such monolithic materials may have broad uses besides catalysis.

cond-mat.mtrl-sci↗

arXiv2021

A durable and efficient electrocatalyst for saline water splitting with current density exceeding 2000 mA cm -2

Water electrolysis is promising for industrial hydrogen production to achieve a sustainable and green hydrogen economy, but the high cost of the technology limits its market share. Developing efficient yet economic electrocatalysts is crucial to decrease the cost of electricity and electrolytic cell. Meanwhile, electrolysis in seawater electrolyte can further reduce feedstock cost. Here we synthesize a type of electrocatalyst where trace precious metals are strongly anchored on corrosion-resistive matrix. As an example, the produced Pt/Ni-Mo electrocatalyst only needs an overpotential of 113 mV to reach an ultrahigh current density of 2000 mA cm-2 in saline-alkaline electrolyte, standing as the best performance so far. It shows high activity and long durability in various electrolytes and under harsh conditions, including strong alkaline and simulated seawater electrolytes, and under elevated temperatures up to 80 degree Celsius). This electrocatalyst is produced on a large scale at low cost and shows good performance in a commercial membrane electrode assembly stack, demonstrating its feasibility for practical water electrolysis

physics.chem-ph↗

arXiv2021

Stabilized Hydroxide Mediated Nickel-Based Electrocatalysts for High Current Density Hydrogen Evolution in Alkaline Media

Large scale production of hydrogen by electrochemical water splitting is considered as a promising technology to address critical energy challenges caused by the extensive use of fossil fuels. Although nonprecious nickel-based catalysts work well at low current densities, they need large overpotentials at high current densities that hinders their potential applications in practical industry. Here we report a hydroxide-mediated nickel based electrocatalyst for high current density hydrogen evolution, which delivers a current density of 1000 mA cm-2 at an overpotential of 98 mV. Combined X-ray absorption spectroscopy and high resolution X-ray photoelectron spectroscopy results show charge redistribution of nickel sites caused by Mo and surface FeOx clusters, which can stabilize the surface nickel hydroxide at high current densities for promoting water dissociation step. Such catalyst is synthesized at the metre scale and shows a current density of 500 mA cm-2 at 1.56 V in the overall water splitting, which demonstrate its potential for practical use. This work highlights a charge-engineering strategy for rational design of catalysts that work well at high current densities.

physics.chem-ph↗

arXiv2021

Coexistence of intrinsic piezoelectricity, ferromagnetism and nontrivial band topology in Li-decorated Janus monolayer $\mathrm{Fe_2SSe}$ with high Curie temperature

Recently, the quantum anomalous Hall (QAH) insulators are predicted in Lithium-decorated iron-based superconductor monolayer materials (LiFeX (X=S, Se and Te)) with very high Curie temperature (\textcolor[rgb]{0.00,0.00,1.00}{PRL 125, 086401 (2020)}), which combines the topological and ferromagnetic (FM) orders. It is interesting and useful to achieve coexistence of intrinsic piezoelectricity, ferromagnetism and nontrivial band topology in single two-dimensional (2D) material, namely 2D piezoelectric quantum anomalous hall insulator (PQAHI). In this work, 2D Janus monolayer $\mathrm{Li_2Fe_2SSe}$ is predict to be a room-temperature PQAHI, which possesses dynamic, mechanical and thermal stabilities. It is predicted to be a half Dirac semimetal without spin-orbit coupling (SOC). It is found that the inclusion of SOC opens up a large nontrivial gap, which means the nontrivial bulk topology (QAH insulator), confirmed by the calculation of Berry curvature and the presence of two chiral edge states (Chern number C=2). Calculated results show that monolayer $\mathrm{Li_2Fe_2SSe}$ possesses robust QAH states against biaxial strain and electronic correlations. Compared to LiFeX, the glide mirror $G_z$ of $\mathrm{Li_2Fe_2SSe}$ disappears, which will induce only out-of-plane piezoelectric response. The calculated out-of-plane $d_{31}$ of monolayer $\mathrm{Li_2Fe_2SSe}$ is -0.238 pm/V comparable with ones of other 2D known materials. Moreover, very high Curie temperature (about 1000 K) is predicted by using Monte Carlo (MC) simulations, which means that the QAH effect can be achieved at room temperature in Janus monolayer $\mathrm{Li_2Fe_2SSe}$. Similar to monolayer $\mathrm{Li_2Fe_2SSe}$, the PQAHI can also be realized in the Janus monolayer $\mathrm{Li_2Fe_2SeTe}$.

cond-mat.mtrl-sci↗

arXiv2020

Structure-driven intercalated architecture of septuple-atomic-layer $MA_2Z_4$ family with diverse properties from semiconductor to topological insulator to Ising superconductor

Motivated by the fact that septuple-atomic-layer MnBi$_2$Te$_4$ can be structurally viewed as the combination of double-atomic-layer MnTe intercalating into quintuple-atomic-layer Bi$_2$Te$_3$, we present a general approach of constructing twelve septuple-atomic-layer $α_i$- and $β_i$-$MA_2Z_4$ monolayer family (\emph{i} = 1 to 6) by intercalating MoS$_2$-type $MZ$$_2$ monolayer into InSe-type A$_2$Z$_2$ monolayer. Besides reproducing the experimentally synthesized $α_1$-MoSi$_2$N$_4$, $α_1$-WSi$_2$N$_4$ and $β_5$-MnBi$_2$Te$_4$ monolayer materials, another 66 thermodynamically and dynamically stable $MA_2Z_4$ were predicted, which span a wide range of properties upon the number of valence electrons (VEC). $MA_2Z_4$ with the rules of 32 or 34 VEC are mostly semiconductors with direct or indirect band gap and, however, with 33 VEC are generally metal, half-metal ferromagnetism, or spin-gapless semiconductor upon whether or not an unpaired electron is spin polarized. Moreover, we propose $α_2$-WSi$_2$P$_4$ for the spin-valley polarization, $α_1$-TaSi$_2$N$_4$ for Ising superconductor and $β_2$-SrGa$_2$Se$_4$ for topological insulator.

cond-mat.mtrl-sci↗

arXiv2020

Proton and Li-Ion Permeation through Graphene with Eight-Atom-Ring Defects

Defect-free graphene is impermeable to gases and liquids but highly permeable to thermal protons. Atomic-scale defects such as vacancies, grain boundaries and Stone-Wales defects are predicted to enhance graphene's proton permeability and may even allow small ions through, whereas larger species such as gas molecules should remain blocked. These expectations have so far remained untested in experiment. Here we show that atomically thin carbon films with a high density of atomic-scale defects continue blocking all molecular transport, but their proton permeability becomes ~1,000 times higher than that of defect-free graphene. Lithium ions can also permeate through such disordered graphene. The enhanced proton and ion permeability is attributed to a high density of 8-carbon-atom rings. The latter pose approximately twice lower energy barriers for incoming protons compared to the 6-atom rings of graphene and a relatively low barrier of ~0.6 eV for Li ions. Our findings suggest that disordered graphene could be of interest as membranes and protective barriers in various Li-ion and hydrogen technologies.

cond-mat.mtrl-sci↗

arXiv2016

Direct Observation of Layer-Dependent Electronic Structure in Phosphorene

Phosphorene, a single atomic layer of black phosphorus, has recently emerged as a new twodimensional (2D) material that holds promise for electronic and photonic technology. Here we experimentally demonstrate that the electronic structure of few-layer phosphorene varies significantly with the number of layers, in good agreement with theoretical predictions. The interband optical transitions cover a wide, technologically important spectrum range from visible to mid-infrared. In addition, we observe strong photoluminescence in few-layer phosphorene at energies that match well with the absorption edge, indicating they are direct bandgap semiconductors. The strongly layer-dependent electronic structure of phosphorene, in combination with its high electrical mobility, gives it distinct advantages over other twodimensional materials in electronic and opto-electronic applications.

cond-mat.mtrl-sci↗