Jiuxiang Dai

Quasi-paired Pt atoms, distinguished by closely-neighboring and yet non-contiguous Pt single atoms acting in synergy, are stabilized on a mesoporous Mo₂C support. The Pt_quasi/Mo₂C exhibits much superior selectivity and mass activity toward four-electron oxygen reduction pathway as compared to both isolated Pt single atoms and Pt nanoparticles, owing to the unique O─O activation mechanism enabled by the quasi-paired Pt atoms.

Abstract

Atomically dispersed Pt species are advocated as a promising electrocatalyst for the oxygen reduction reaction (ORR) to boost noble metal utilization efficiency. However, when assembled on various substrates, isolated Pt single atoms are often demonstrated to proceed through the two-electron ORR pathway due to the unfavorable O─O bond cleavage thermodynamics in the absence of catalytic ensemble sites. In addition, although their distinct local coordination environments at the exact single active sites are intensively explored, the interactions and synergy between closely neighboring single atom sites remain elusive. Herein, atomically dispersed Pt monomers strongly interacting on a Mo₂C support is demonstrated as a model catalyst in the four-electron ORR, and the beneficial interactions between two closely neighboring and yet non-contiguous Pt single atom sites (named as quasi-paired Pt single atoms) are shown. Compared to isolated Pt single atom sites, the quasi-paired Pt single atoms deliver a superior mass activity of 0.224 A mg⁻¹ _Pt and near-100% selectivity toward four-electron ORR due to the synergistic interaction from the two quasi-paired Pt atom sites in modulating the binding mode of reaction intermediates. Our first-principles calculations reveal a unique mechanism of such quasi-paired configuration for promoting four-electron ORR.

The Computational 2D Materials Database (C2DB) is a highly curated open database organising a wealth of computed properties for more than 4000 atomically thin two-dimensional (2D) materials. Here we report on new materials and properties that were added to the database since its first release in 2018. The set of new materials comprise several hundred monolayers exfoliated from experimentally known layered bulk materials, (homo)bilayers in various stacking configurations, native point defects in semiconducting monolayers, and chalcogen/halogen Janus monolayers. The new properties include exfoliation energies, Bader charges, spontaneous polarisations, Born charges, infrared polarisabilities, piezoelectric tensors, band topology invariants, exchange couplings, Raman spectra and second harmonic generation spectra. We also describe refinements of the employed material classification schemes, upgrades of the computational methodologies used for property evaluations, as well as signifi...

An all-around-type player in the field of photoinduced phosphorescence material is presented, whose room-temperature phosphorescence (RTP) efficiency can increase from near 0% to 22% after continuous UV irradiation. The high RTP efficiency and good photostability make these materials exhibit an attractive prospect for potential applications in many fields, including leak tests, microcrack detection, programmable information storage, and encryption.

Abstract

The research of purely organic room-temperature phosphorescence (RTP) materials with stimulus response characteristic has drawn increasing attention for their broad application prospects. However, these kinds of materials are really scarce now, especially for those with efficient RTP emissions, which have largely limited their practical applications. Here, an all-around-type player in the field of photoinduced phosphorescence material appears, whose RTP efficiency can increase from near 0 to 22% after continuous UV irradiation. Correspondingly, the UV-written patterns based on them can be clearly observed by the naked eye in daytime or even under sunlight. Moreover, these materials are found to show excellent photostability, and the strong RTP emission can still be observed after repeated activation for more than 50 times. The high RTP efficiency and good photostability make these photoinduced RTP materials exhibit an attractive prospect for potential applications in many fields, including leak test, microcrack detection, programmable information storage, and encryption.

A photothermoelectric effect in 2D material PdSe₂ with high anisotropy is revealed through scanning photocurrent microscopy measurement at zero bias. Performance parameters based on the photothermoelectric effect are investigated experimentally, including response speed, air-stability, broadband spectrum response, reasonable responsivity, and polarization-resolved optical response. An ultrafast response speed (≈4 µs) and anisotropic photoresponse with a ratio up to ≈1.3 are observed.

Abstract

PdSe₂, a star photosensitive functional material, has been successfully used in photodetectors based on sensing mechanisms of photogating, photoconductive, and photovoltaic effects. Here, a photothermoelectric (PTE) effect is observed in photodetectors based on PdSe₂ flakes grown by chemical vapor deposition. The unique photoresponse arises from an electron temperature gradient instead of electron–hole separation. Direct evidence of the PTE effect is confirmed by a nonlocal photoresponse under zero bias. Moreover, the PdSe₂ photodetector shows high performance in terms of ultrafast response speed (4 µs), high air-stability, broadband spectrum photodetection, reasonable responsivity, and anisotropic optical response. This study paves a new way for developing high-performance photodetectors based on PdSe₂ layered materials.

A highly transparent, efficient, and stable 2D (〈n〉 = 2, according to the precursor stoichiometry) perovskite semitransparent photovoltaic (ST-PV) is demonstrated for application in building-integrated photovoltaics. By fully expanding the phase distribution and enhancing the out-of-plane orientation, the first average 〈n〉 = 2 2D ST-PV is realized with an average visible transmittance over 40% and power conversion efficiency of 7.52%.

Abstract

The application of low average layer-number (〈n〉 ≤ 2) 2D perovskites in semitransparent photovoltaics (ST-PVs) has been hindered by their strong exciton binding energy and high electrical anisotropy. Here, the phase distribution is expanded fully and orderly to enable efficient charge transport in 2D (NMA)₂(MA)Pb₂I₇ (NMA: 1-naphthylmethylammonium, MA: CH₃NH₃ ⁺) perovskite films by regulating the sedimentation dynamics of organic cation-based colloids. Ammonium chloride is synergistically introduced to enhance the phase separation further and construct a favorable out-of-plane orientation. The wide and graded phase distribution well aligns the energy level to facilitate charge transfer. As a result, the first application of an average 〈n〉 = 2 2D perovskite is implemented in ST-PVs with visible power conversion efficiency (PCE) of 7.52% and high average visible transmittance (AVT) of 40.5%. This study offers a new candidate and an effective strategy for efficient and stable ST-PVs and is relevant to other perovskite optoelectronic devices.

This article reviews the current understanding of the structure–property–function relationship of the graphitic carbon nitride family of materials, covering their historical developments, characterization methodologies, chemical and opto–electronic properties, carrier dynamics, and catalytic reactivity. The focus is on the materials’ structures across three dimensions as the origin of these properties, highlighting topics on which there is a consensus, and those still contentious for future research.

Abstract

Despite the explosion in the number of publications on the graphitic carbon nitride family of materials, much still remains unknown about their structure and the underlying properties responsible for their various applications. This critical review covers the state-of-the-art in the understanding of their structure–property–photocatalysis relationship, from their molecular constituents to stacking as a (quasi) two-dimensional structure, highlighting the areas in which there is wide agreement and those still unresolved. This review first recounts how the structural understanding of these materials has evolved since the 19th century, followed by a commentary on the best practice for unambiguously characterizing their molecular structure and two-dimensional stacking arrangements. The recent literature is then examined to elucidate how individual molecular moieties affect their various material properties, particularly their chemical and opto–electronic properties, carrier dynamics, and catalytic reactivity, and how their use for energy applications can be impacted by the structural features across each dimension. Lastly, the translation of the aforementioned fundamental insights to rational molecular design is demonstrated, highlighting the synthesis of heptazine-based materials for order-of-magnitude improvement in photocatalytic reactivity, as well as the unusual phenomenon of stabilization of light-induced electrons, an effect currently exploited for a new paradigm in solar energy storage.

The nanoporous carbon derived from 6FDA-based polyimide reveals confined pore structure sized suitable for the separation of liquid hydrocarbons. Rigid ultramicropores in 6FDA−DAM carbon molecular sieve (CMS) hollow fiber membranes enable molecular discrimination of hexane isomers based on size and shape difference via ‘organic solvent forward osmosis (OSFO)’ without pressurization at room temperature.

Abstract

Liquid-phase chemical separations from complex mixtures of hydrocarbon molecules into singular components are large-scale and energy-intensive processes. Membranes with molecular specificity that efficiently separate molecules of similar size and shape can avoid phase changes, thereby reducing the energy intensity of the process. Here, forward osmosis molecular differentiation of hexane isomers through a combination of size- and shape-based separation of molecules is demonstrated. An ultramicroporous carbon membrane produced with 6FDA-polyimides realized the separation of isomers for different shapes of di-branched, mono-branched, and linear molecules. The draw solvents provide the driving force for fractionation of hexane isomers with a sub-0.1 nm size difference at room temperature without liquid-phase pressurization. Such membranes could perform bulk chemical separations of organic liquids to achieve major reductions in the energy intensity of the separation processes.

Plasmonic ultrathin PtAg nanosheets are discovered to have strong broadband photothermal and photoacoustic effect for photothermal therapy (PTT) and photoacoustic imaging (PAI) of tumors in both the first near-infrared (NIR-I) and second near-infrared (NIR-II) biowindows.

Abstract

Broadband near-infrared (NIR) photothermal and photoacoustic agents covering from the first NIR (NIR-I) to the second NIR (NIR-II) biowindow are of great significance for imaging and therapy of cancers. In this work, ultrathin two-dimensional plasmonic PtAg nanosheets are discovered with strong broadband light absorption from NIR-I to NIR-II biowindow, which exhibit outstanding photothermal and photoacoustic effects under both 785 and 1064 nm lasers. Photothermal conversion efficiencies (PCEs) of PtAg nanosheets reach 19.2% under 785 nm laser and 45.7% under 1064 nm laser. The PCE under 1064 nm laser is higher than those of most reported inorganic NIR-II photothermal nanoagents. After functionalization with folic acid modified thiol-poly(ethylene glycol) (SH-PEG-FA), PtAg nanosheets endowed with good biocompatibility and 4T1 tumor-targeted function give high performances for photoacoustic imaging (PAI) and photothermal therapy (PTT) in vivo under both 785 and 1064 nm lasers. The effective ablation of tumors in mice can be realized without side effects and tumor metastasis by PAI-guided PTT of PtAg nanosheets under 785 or 1064 nm laser. The results demonstrate that the prepared PtAg nanosheets with ultrathin thickness and small size can serve as a promising phototheranostic nanoplatform for PAI-guided PTT of tumors in both NIR-I and NIR-II biowindows.

S-decorated porous Ti₃C₂ MXene is used as effective selenium host, giving high capacity, rate capability, and long lifespan of Na–Se batteries. The S-decorated interfaces combined with in situ forming Cu₂Se facilitate the immobilization and transformation of polyselenides and thus lead to efficient surface-dominated capacitive behavior.

Given natural abundance of Na and superior kinetics of Se, Na–Se batteries have attracted much attention but still face the problem of shuttling effect of soluble intermediates. The first-principle calculations reveal the S-decorated Ti₃C₂ exhibits increased binding energy to sodium polyselenides, suggesting a better capture and restriction on intermediates. The obtained Se@S-decorated porous Ti₃C₂ (Se@S-P-Ti₃C₂) exhibits a high reversible capacity of 765 mAh g⁻¹ at 0.1 A g⁻¹ (calculated based on Se), ≈1.2, 1.3, and 1.7 times of Se@porous Ti₃C₂ (Se@P-Ti₃C₂), Se@Ti₃C₂, and Se, respectively. It gives considerable capacity of 664 mAh g⁻¹ at 20 A g⁻¹ and impressive cycling stability over 2300 cycles with an ultralow capacity decay of 0.003% per cycle. The excellent electrochemical performance can be ascribed to the S-modified porous Ti₃C₂, which provides effective immobilization toward polyselenides, makes full use of nanosized Se, and alleviates volume expansion during sodiation/desodiation. Additionally, in situ forming Cu₂Se can generate Cu nanoparticles through discharge process and then transform polyselenides into solid-phase Cu₂Se, further suppressing the shuttling effect. This work provides a practical strategy to immobilize and transform sodium polyselenides for high-capacity and long-life Na–Se batteries.

npj 2D Materials and Applications, Published online: 09 July 2021; doi:10.1038/s41699-021-00245-w

Two dimensional V₂O₃ and its experimental feasibility as robust room-temperature magnetic Chern insulator

2D metal chalcogenide heterostructures (2DMCHs) are a current research hotspot due to their unique properties. The review highlights research advances in controllable chemical vapor deposition growth of 2DMCHs, focusing on additives-assisted process, substrate engineering, and mass transfer process. The novel applications and physical phenomenon of 2DMCHs in memory, infrared photodetector, and moiré superlattice are also considered.

Abstract

There has been a renewed interest in 2D metal chalcogenide heterostructures (2DMCHs) in the context of their exceptional optoelectronic properties and potential for a wide variety of practical applications. However, the controllable synthesis of 2DMCHs remains a huge challenge. Recently, chemical vapor deposition (CVD) has been proposed to be an efficient way to realize high-quality, large-scale, and layer-controllable 2D materials and has also shown high feasibility in 2DMCHs. Here, the latest controllable CVD growth strategies of 2DMCHs are introduced. The designed growth techniques mainly focus on three vital factors in CVD: source supply, mass transport, and substrate engineering. Then, the emerging novel applications of 2DMCHs are also systematically reviewed with particular attention to memory, infrared photodetector, and moiré superlattice, which have demonstrated significant progress in recent years. Finally, future opportunities and remaining challenges concerning the developments of 2DMCHs are presented.

This work develops an in situ investigation system to study the growth and self-assembly of graphene on liquid copper in real-time. The translation and rotation behavior of graphene are captured for the first time, which is attributed to the fluidity of liquid copper surface. The self-assembly mechanism is further revealed, enabling the precise synthesis of various assembly structures.

Abstract

The in situ investigation of the dynamic growth process and novel assembly phenomena of graphene on liquid copper (Cu) is of great significance to deeply understand the special behavior of graphene and self-assembly mechanism. Here, the direct observation of the graphene growth and motion behavior on liquid Cu via in situ imaging is reported. Evidence of graphene movement on liquid Cu is offered and it is demonstrated that the translation and rotation behaviors of graphene are affected by the surface condition of liquid Cu. The self-assembly process of graphene array is also revealed by capturing the dynamic changes of graphene in real-time. Further analysis highlights the importance of surface energy of liquid Cu and the interaction between graphene building blocks during the self-assembling process. The growth parameters are also investigated to flexibly control the assembly configuration of graphene arrays. This work provides an insight into the mechanism of graphene motion and assembly behavior that can be used to guide the controllable manipulation of 2D materials and on-demand fabrication assembly structures with desired properties.

This study reports large anomalous Hall and Nernst effects in high Curie-temperature Iron-based Heusler compounds. The positive effect of anti-site disorder on the anomalous Hall transport is revealed. Considering the very high Curie temperature (nearly 1000 K), larger Nernst thermopowers at high temperatures are expected in the studied compounds owing to the existing magnetic order and the intrinsic Berry curvature.

Abstract

The interplay between topology and magnetism has recently sparked the frontier studies of magnetic topological materials that exhibit intriguing anomalous Hall and Nernst effects owning to the large intrinsic Berry curvature (BC). To better understand the anomalous quantum transport properties of these materials and their implications for future applications such as electronic and thermoelectric devices, it is crucial to discover more novel material platforms for performing anomalous transverse transport studies. Here, it is experimentally demonstrated that low-cost Fe-based Heusler compounds exhibit large anomalous Hall and Nernst effects. An anomalous Hall conductivity of 250–750 S cm⁻¹ and Nernst thermopower of above 2 µV K⁻¹ are observed near room temperature. The positive effect of anti-site disorder on the anomalous Hall transport is revealed. Considering the very high Curie temperature (nearly 1000 K), larger Nernst thermopowers at high temperatures are expected owing to the existing magnetic order and the intrinsic BC. This work provides a background for developing low-cost Fe-based Heusler compounds as a new material platform for anomalous transport studies and applications, in particular, near and above room temperature.

Nature Electronics, Published online: 09 July 2021; doi:10.1038/s41928-021-00621-w

Author Correction: Resonant tunnelling diodes based on twisted black phosphorus homostructures

2D ferroelectric field-effect transistors devices are fabricated by epitaxial growth of Bi₂O₂Se on Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃. The devices exhibit ferroelectric polarization-dependent photoresponse upon visible light (λ = 405 nm) and infrared light (IR, λ = 980 nm) illumination. Combining optical stimuli with ferroelectric gating, the devices show not only nonvolatile memory and optoelectronic response, but also coincidence detection of visible and infrared light.

Abstract

Information processing with optoelectronic devices provides an alternative way to efficiently process hybrid optical and electronic signals. Ferroelectric field-effect transistors (FeFETs) can effectively respond to external optical and electrical stimuli by modulating their polarization states. Here, a 2D FeFET is demonstrated by the epitaxial growth of high-quality 2D bismuth layered oxyselenide (Bi₂O₂Se) films on PMN-PT(001) ferroelectric single-crystal substrates. Upon switching the polarization direction of PMN-PT, the authors realize in situ, reversible, and nonvolatile manipulation of the resistance of Bi₂O₂Se thin film (≈877%). The device simultaneously exhibits a polarization-dependent photoresponse through visible light (λ = 405 nm) and infrared light (IR, λ = 980 nm) illumination. Combining optical stimuli with ferroelectric gating, it is demonstrated that the devices not only show nonvolatile memory and optoelectronic responses, but also show coincidence detection of visible and IR light. This work holds great potential in constructing new multiresponse and multifunction 2D-FeFETs.