A fingerprint-like supramolecular-assembled Ag3PO4/polydopamine/g-C3N4 heterojunction nanocomposite for enhanced solar-driven oxygen evolution in vivo.

Biocompatible photocatalytic water-splitting systems are promising for tissue self-oxygenation. Herein, a structure-function dual biomimetic fingerprint-like silver phosphate/polydopamine/graphitic carbon nitride (Ag3PO4/PDA/g-C3N4) heterojunction nanocomposite is proposed for enhanced solar-driven oxygen (O2) evolution in vivo in situ. Briefly, a porous nitrogen-defected g-C3N4 nanovoile (CN) is synthesized as the base. Dopamine molecules are controllably inserted into the CN interlayer, forming PDA spacers (4.28 nm) through self-polymerization-induced supramolecular-assembly. Ag3PO4 nanoparticles are then in situ deposited to create Ag3PO4/PDA/CN. The fingerprint-like structure of PDA/CN enlarges the layer spacing, thereby accelerating mass transfer and increasing reaction sites. The PDA spacer roles as excellent light harvester, electronic-ionic conductor, and redox pair through conformational changes, resulting in tailored electronic band structure, optimized carrier behavior, and reduced electrochemical impedance. In physiological conditions, Ag3PO4/PDA/CN exhibits O2 evolution rate of 45.35 µmol⋅g-1⋅h-1, 9-fold of bulk g-C3N4. The biocompatibility and in vivo oxygen supply effectiveness for biomedical applications have been verified in animal models.

Conductive catalysis by subsurface transition metals.

The nature of catalysis has been hotly pursued for over a century, and current research is focused on understanding active centers and their electronic structures. Herein, the concept of conductive catalysis is proposed and verified by theoretical simulations and experimental observations. Metallic systems containing buried catalytically active transitional metals and exposed catalytically inert main group metals are constructed, and the electronic interaction between them via metallic bonding is disclosed. Through the electronic interaction, the catalytic properties of subsurface transitional metals (Pd or Rh) can be transferred to outermost main group metals (Al or Mg) for several important transformations like semi-hydrogenation, Suzuki-coupling and hydroformylation. The catalytic force is conductive, in analogy with the magnetic force and electrostatic force. The traditional definition of active centers is challenged by the concept of conductive catalysis and the electronic nature of catalysis is more easily understood. It might provide new opportunities for shielding traditional active centers against poisoning or leaching and allow for precise regulation of their catalytic properties by the conductive layer.

Highly Efficient and Stable Methane Dry Reforming Enabled by a Single-Site Cationic Ni Catalyst.

Zeolite-supported nickel (Ni) catalysts have been extensively studied for the dry reforming of methane (DRM). It is generally believed that prior to or during the reaction, Ni is reduced to a metallic state to act as the catalytic site. Here, we employed a ligand-protected synthesis method to achieve a high degree of Ni incorporation into the framework of the MFI zeolite. The incorporated Ni species retained their cationic nature during the DRM reaction carried out at 600 °C, exhibiting higher apparent catalytic activity and significantly greater catalytic stability in comparison to supported metallic Ni particles at the same loading. From theoretical and experimental evidence, we conclude that the incorporation of Ni into the zeolite framework leads to the formation of metal-oxygen (Niδ+-O(2-ξ)-) pairs, which serve as catalytic active sites, promoting the dissociation of C-H bonds in CH4 through a mechanism distinct from that of metallic Ni. The conversion of CH4 on cationic Ni single sites follows the CHx oxidation pathway, which is characterized by the rapid transformation of partial cracking intermediates CHx*, effectively inhibiting coke formation. The presence of the CHx oxidation pathway was experimentally validated by identifying the reaction intermediates. These new mechanistic insights elucidate the exceptional performance of the developed Ni-MFI catalyst and offer guidance for designing more efficient and stable Ni-based DRM catalysts.

Ferromagnetic ordering correlated strong metal-oxygen hybridization for superior oxygen reduction reaction activity.

The efficiency of transition-metal oxide materials toward oxygen-related electrochemical reactions is classically controlled by metal-oxygen hybridization. Recently, the unique magnetic exchange interactions in transition-metal oxides are proposed to facilitate charge transfer and reduce activation barrier in electrochemical reactions. Such spin/magnetism-related effects offer a new and rich playground to engineer oxide electrocatalysts, but their connection with the classical metal-oxygen hybridization theory remains an open question. Here, using the MnxVyOz family as a platform, we show that ferromagnetic (FM) ordering is intrinsically correlated with the strong manganese (Mn)-oxygen (O) hybridization of Mn oxides, thus significantly increasing the oxygen reduction reaction (ORR) activity. We demonstrate that this enhanced Mn-O hybridization in FM Mn oxides is closely associated with the generation of active Mn sites on the oxide surface and obtaining favorable reaction thermodynamics under operating conditions. As a result, FM-Mn2V2O7 with a high degree of Mn-O hybridization achieves a record high ORR activity. Our work highlights the potential applications of magnetic oxide materials with strong metal-oxygen hybridization in energy devices.

Bilayer Kagome Borophene with Multiple van Hove Singularities.

The appearance of van Hove singularities near the Fermi level leads to prominent phenomena, including superconductivity, charge density wave, and ferromagnetism. Here a bilayer Kagome lattice with multiple van Hove singularities is designed and a novel borophene with such lattice (BK-borophene) is proposed by the first-principles calculations. BK-borophene, which is formed via three-center two-electron (3c-2e) σ-type bonds, is predicted to be energetically, dynamically, thermodynamically, and mechanically stable. The electronic structure hosts both conventional and high-order van Hove singularities in one band. The conventional van Hove singularity resulting from the horse saddle is 0.065 eV lower than the Fermi level, while the high-order one resulting from the monkey saddle is 0.385 eV below the Fermi level. Both the singularities lead to the divergence of electronic density of states. Besides, the high-order singularity is just intersected to a Dirac-like cone, where the Fermi velocity can reach 1.34 × 106  m s-1 . The interaction between the two Kagome lattices is critical for the appearance of high-order van Hove singularities. The novel bilayer Kagome borophene with rich and intriguing electronic structure offers an unprecedented platform for studying correlation phenomena in quantum material systems and beyond.

Quinoxalineimide-Based Semiconducting Polymer Nanoparticles as an Effective Phototheranostic for the Second Near-Infrared Fluorescence Imaging and Photothermal Therapy.

Multifunctional theranostics play a critical role in improving the efficacy of photothermal therapy and tumor fluorescence imaging; however, they require the integration of complex components into a single theranostic system, and their response in the second near-infrared (NIR-II) region is constrained by wavelengths of a photosensitizer. To address this issue, we herein developed a novel multifunctional thiazole-fused quinoxalineimide semiconducting polymer (named PQIA-BDTT), which exhibits NIR-II fluorescence and photothermal properties. PQIA-BDTT nanoparticles achieved an impressively high photothermal conversion efficiency (72.6%) in laser (1064 nm)-induced photothermal therapy at a safe maximum permissible exposure, demonstrating their capability as an effective photothermal agent. Moreover, PQIA-BDTT nanoparticles can be used as a reference for NIR-II fluorescence imaging under a low laser fluence. The tumor size and location in 4T1 mice intravenously injected with the PQIA-BDTT nanoparticles could be precisely identified through NIR-II fluorescence imaging, which also exhibited remarkable photothermal antitumor efficacy by in vitro and in vivo therapy. Overall, this study demonstrates that introducing a thiazole-fused quinoxalineimide acceptor unit into a donor-acceptor conjugated polymer is an effective strategy for the synthesis of novel multifunctional theranostic systems, which provides a novel platform for designing theranostic agents for biomedical applications.

Moiré-Pattern Modulated Electronic Structures of GaSe/HOPG Heterostructure.

Conventional two-dimensional electron gas (2DEG) typically occurs at the interface of semiconductor heterostructures and noble metal surfaces, but it is scarcely observed in individual 2D semiconductors. In this study, few-layer gallium selenide (GaSe) grown on highly ordered pyrolytic graphite (HOPG) is demonstrated using scanning tunneling microscopy and spectroscopy (STM/STS), revealing that the coexistence of quantum well states (QWS) and 2DEG. The QWS are located in the valence bands and exhibit a peak feature, with the number of quantum wells being equal to the number of atomic layers. Meanwhile, the 2DEG is located in the conduction bands and exhibits a standing-wave feature. Additionally, monolayer GaSe/HOPG heterostructures with different stacking angles (0°, 33°, 8°) form distinct moiré patterns that arise from lattice mismatch and angular rotation between adjacent atomic layers in 2D materials, which effectively modulate the electron effective mass, charge redistribution, and band gap of GaSe. Overall, this work reveals a paradigm of band engineering based on layer numbers and moiré patterns that can modulate the electronic properties of 2D materials.

Enhanced Electron-Hole Separation in Phosphorus-Coordinated Co Atom on g-C3N4 toward Photocatalytic Overall Water Splitting.

Revealing the decoration mode of g-C3N4 and understanding the physical mechanism of overall water splitting is important for the further improvement of the photocatalytic activity of g-C3N4-based materials. With core level shift and molecular dynamics simulations based on first-principles calculations, Co1(PHx)3 anchored on the triazine of g-C3N4 is determined as a stable single-atom catalyst with high efficiency for photocatalytic overall water splitting. The separated spin-polarized charge density distribution of valence-band maximum and conduction-band minimum states is beneficial for the long lifetime of photoexcited electrons and holes. An anchored Co single atom site is the active site for oxygen evolution reaction, and nitrogen atoms act as active sites for hydrogen evolution reaction. This new decoration mode of g-C3N4 opens a possible way to functionalize g-C3N4 on both triazine and void sites to realize the separation of OER and hydrogenation reaction by water splitting.

Tuning Fe Spin Moment in Fe-N-C Catalysts to Climb the Activity Volcano via a Local Geometric Distortion Strategy.

As the most promising alternative to platinum-based catalysts for cathodic oxygen reduction reaction (ORR) in proton exchange membrane fuel cells, further performance enhancement of Fe-N-C catalysts is highly expected to promote their wide application. In Fe-N-C catalysts, the single Fe atom forms a square-planar configuration with four adjacent N atoms (D4h symmetry). Breaking the D4h symmetry of the FeN4 active center provides a new route to boost the activity of Fe-N-C catalysts. Herein, for the first time, the deformation of the square-planar coordination of FeN4 moiety achieved by introducing chalcogen oxygen groups (XO2 , X = S, Se, Te) as polar functional groups in the Fe-N-C catalyst is reported. The theoretical and experimental results demonstrate that breaking the D4h symmetry of FeN4 results in the rearrangement of Fe 3d electrons and increases spin moment of Fe centers. The efficient spin state manipulation optimizes the adsorption energetics of ORR intermediates, thereby significantly promoting the intrinsic ORR activity of Fe-N-C catalysts, among which the SeO2 modified catalyst lies around the peak of the ORR volcano plot. This work provides a new strategy to tune the local coordination and thus the electronic structure of single-atom catalysts.

Interface engineering breaks both stability and activity limits of RuO2 for sustainable water oxidation.

Designing catalytic materials with enhanced stability and activity is crucial for sustainable electrochemical energy technologies. RuO2 is the most active material for oxygen evolution reaction (OER) in electrolysers aiming at producing 'green' hydrogen, however it encounters critical electrochemical oxidation and dissolution issues during reaction. It remains a grand challenge to achieve stable and active RuO2 electrocatalyst as the current strategies usually enhance one of the two properties at the expense of the other. Here, we report breaking the stability and activity limits of RuO2 in neutral and alkaline environments by constructing a RuO2/CoOx interface. We demonstrate that RuO2 can be greatly stabilized on the CoOx substrate to exceed the Pourbaix stability limit of bulk RuO2. This is realized by the preferential oxidation of CoOx during OER and the electron gain of RuO2 through the interface. Besides, a highly active Ru/Co dual-atom site can be generated around the RuO2/CoOx interface to synergistically adsorb the oxygen intermediates, leading to a favourable reaction path. The as-designed RuO2/CoOx catalyst provides an avenue to achieve stable and active materials for sustainable electrochemical energy technologies.

Nearly Ideal Two-Dimensional Electron Gas Hosted by Multiple Quantized Kronig-Penney States Observed in Few-Layer InSe.

A theoretical ideal two-dimensional electron gas (2DEG) was characterized by a flat density of states independent of energy. Compared with conventional two-dimensional free-electron systems in semiconductor heterojunctions and noble metal surfaces, we report here the achievement of ideal 2DEG with multiple quantized states in few-layer InSe films. The multiple quantum well states (QWSs) in few-layer InSe films are found, and the number of QWSs is strictly equal to the number of atomic layers. The multiple stair-like DOS as well as multiple bands with parabolic dispersion both characterize ideal 2DEG features in these QWSs. Density functional theory calculations and numerical simulations based on quasi-bounded square potential wells described as the Kronig-Penney model provide a consistent explanation of 2DEG in the QWSs. Our work demonstrates that 2D van der Waals materials are ideal systems for realizing 2DEG hosted by multiple quantized Kronig-Penney states, and the semiconducting nature of the material provides a better chance for construction of high-performance electronic devices utilizing these states, for example, superlattice devices with negative differential resistance.

Ultrathin Van der Waals Antiferromagnet CrTe3 for Fabrication of In-Plane CrTe3 /CrTe2 Monolayer Magnetic Heterostructures.

Ultrathin van der Waals (vdW) magnets are heavily pursued for potential applications in developing high-density miniaturized electronic/spintronic devices as well as for topological physics in low-dimensional structures. Despite the rapid advances in ultrathin ferromagnetic vdW magnets, the antiferromagnetic counterparts, as well as the antiferromagnetic junctions, are much less studied owing to the difficulties in both material fabrication and magnetism characterization. Ultrathin CrTe3 layers have been theoretically proposed to be a vdW antiferromagnetic semiconductor with intrinsic intralayer antiferromagnetism. Herein, the epitaxial growth of monolayer (ML) and bilayer CrTe3 on graphite surface is demonstrated. The structure, electronic and magnetic properties of the ML CrTe3 are characterized by combining scanning tunneling microscopy/spectroscopy and non-contact atomic force microscopy and confirmed by density functional theory calculations. The CrTe3 MLs can be further utilized for the fabrication of a lateral heterojunction consisting of ML CrTe2 and ML CrTe3 with an atomically sharp and seamless interface. Since ML CrTe2 is a metallic vdW magnet, such a heterostructure presents the first in-plane magnetic metal-semiconductor heterojunction made of two vdW materials. The successful fabrication of ultrathin antiferromagnetic CrTe3 , as well as the magnetic heterojunction, will stimulate the development of miniaturized antiferromagnetic spintronic devices based on vdW materials.

Pt Atom on the Wall of Atomic Layer Deposition (ALD)-Made MoS2 Nanotubes for Efficient Hydrogen Evolution.

Single-atom catalysts (SACs) can achieve excellent catalytic efficiency at ultralow catalyst consumptions. Herein, platinum (Pt) atoms are fixed on the wall of atomic layer deposition (ALD)-made molybdenum disulfide nanotube arrays (MoS2 -NTA) for efficient hydrogen evolution reaction (HER). More concretely, MoS2 -NTA with different nanotube diameters and wall thicknesses are fabricated by a sacrificial strategy of anodic aluminum oxide (AAO) template via ALD; then Pt atoms are fixed on the wall of Ti3 C2 -supported MoS2 -NTA as a catalytic system. The MoS2 -NTA/Ti3 C2 decorated with 0.13 wt.% of Pt results in a low overpotential of 32 mV to deliver a current density of 10 mA cm-2 , which is superior to 20 wt.% commercial Pt/C (41 mV). Ordered MoS2 -NTA instead of 2D MoS2 prevents Pt atoms from aggregating and then exerts catalytic activities. The density functional theory calculations suggest that the Pt atoms are more likely to occupy the sites on the tubular MoS2 than the planar MoS2 , and the Pt atoms accumulated at the Mo site of MoS2 -NT have a moderate Gibbs free energy (close to zero).

Activating Inert Surface Pt Single Atoms via Subsurface Doping for Oxygen Reduction Reaction.

The performance of single-atom catalysts strongly depends on their particular coordination environments in the near-surface region. Herein, we discover that engineering extra Pt single atoms in the subsurface (Ptsubsurf) can significantly enhance the catalytic efficiency of surface Pt single atoms toward the oxygen reduction reaction (ORR). We experimentally and theoretically investigated the effects of the Ptsubsurf single atoms implanted in different positions of the subsurface of Co particles. The local environments and catalytic properties of surface Pt1 are highly tunable via Ptsubsurf doping. Specifically, the obtained Pt1@Co/NC catalyst displays a remarkable performance for ORR, achieving mass activity of 4.2 mA µgPt-1 (28 times higher than that of commercial Pt/C) at 0.9 V versus reversible hydrogen electrode (RHE) in 0.1 M HClO4 solution with high stability over 30000 cycles.

Concomitant Photoresponsive Chiroptics and Magnetism in Metal-Organic Frameworks at Room Temperature.

Stimulus-responsive metal-organic frameworks (MOFs) can be used for designing smart materials. Herein, we report a family of rationally designed MOFs which exhibit photoresponsive chiroptical and magnetic properties at room temperature. In this design, two specific nonphotochromic ligands are selected to construct enantiomeric MOFs, {Cu2(L-mal)2(bpy)2(H2O)·3H2O}n (1) and {Cu2(D-mal)2(bpy)2(H2O)·3H2O}n (2) (mal = malate, bpy = 4, 4' - bipyridine), which can alter their color, magnetism, and chiroptics concurrently in response to light. Upon UV or visible light irradiation, long-lived bpy- radicals are generated via photoinduced electron transfer (PET) from oxygen atoms of carboxylates and hydroxyl of malates to bpy ligands, giving rise to a 23.7% increase of magnetic susceptibility at room temperature. The participation of the chromophores (-OH and -COO-) bound with the chiral carbon during the electron transfer process results in a small dipolar transition; thus, the Cotton effects of the enantiomers are weakened along with a photoinduced color change. This work demonstrates that the simultaneous responses of chirality, optics, and magnetism can be achieved in a single compound at room temperature and may open up a new pathway for designing chiral stimuli-responsive materials.

Pd-Pt Tesseracts for the Oxygen Reduction Reaction.

Hollow frame structures are of special interest in the realm of catalysis since they hold only ridges and hollow interiors, enabling the accessibility of active sites to the most extent. Herein, we prepared Pd-Pt hollow frame structures composed of double-shell cubes linked by body diagonals as an efficient catalyst toward the oxygen reduction reaction (ORR), inspired by the 4D analogue of a cube, denoted as a tesseract. The etching process involves the selective removal of Pd atoms and the subsequent rearrangement of the remaining Pd and Pt atoms. The successful preparation of Pd-Pt tesseracts via etching lies in the selection of Pd/Pt ratio in the initial Pd-Pt nanocubes. With various ratios of Pd-Pt nanocubes as templates, we obtained Pd-Pt octapods, tesseracts, and nanoframes, respectively. During the ORR, Pd-Pt tesseracts exhibited the highest mass activity of 1.86 A mg-1Pt among these Pd-Pt nanocrystals. On the basis of mechanistic studies, the high activity of Pd-Pt tesseracts derived from the optimal oxygen adsorption energy due to the facet effect and composition effect.

Surface Nitrogen-Injection Engineering for High Formation Rate of CO2 Reduction to Formate.

In this study, we highlight that surface nitrogen-injection engineering brings a high formation rate for CO2 reduction to formate, which is high level among the reported electrocatalysts. Surface nitrogen-injection engineering can increase the amounts of active sites and optimize the electronic structure simultaneously. Taking an example of SnS2 precursors, the final-obtained surface N-enriched Sn(S) nanosheets (denoted as N-Sn(S) nanosheets) exhibit a 5-fold of current density and 2.45-fold of Faradaic efficiency than pristine SnS2 derived Sn(S) nanosheets (denoted as Sn(S) nanosheets). On account of high activity and selectivity, the formation rate of formate is 14 times than that of pristine samples and reaches up to 1358 µmol h-1 cm-2. Moreover, this strategy is proven to be general to other metal sulfides, such as CuS and In2S3. We anticipate that surface nitrogen-injection engineering offers new avenues to rational design of advanced electrocatalysts for CO2 reduction reaction.

Reversible Potassium Intercalation in Blue Phosphorene-Au Network Driven by an Electric Field.

Foreign atom intercalation into an interface alters the strength of interlayer interaction and leads to the novel types of desirable properties. Here, we report an investigation via scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy (STS) of reversible potassium (K) intercalation in the blue phosphorene (blueP)-Au network that can be locally induced by an external electric field. The unique structure of the blueP-Au network provides large space in its pores for the intercalation and deintercalation process. The X-ray photoemission spectroscopy results reveal that the intercalated K atoms are bonded with Au atoms in substrate, which weakens the interaction between the blueP-Au network and Au(111). The STS and angle-resolved photoemission spectroscopy results indicate that the electronic properties of the blueP-Au network have been modulated after the K intercalation. Such reversible intercalation and deintercalation transitions in the blueP-Au network are relevant for the design of the nanoelectronic devices as well as for its application in K-ion batteries.

Well-Defined Single-Atom Cobalt Catalyst for Electrocatalytic Flue Gas CO2 Reduction.

Single-atom Co catalyst Co-Tpy-C with well-defined sites is synthesized by pyrolysis of a Co terpyridine (Tpy) organometallic complex. The Co-Tpy-C catalyst exhibits excellent activity for the electrochemical CO2 reduction reaction in aqueous electrolyte, with CO faradaic efficiency (FE) of over 95% from -0.7 to -1.0 V (vs RHE). By comparison, catalysts without Co or Tpy ligand added do not show any high CO FE. When simulated flue gas with 15% of CO2 is used as the source of CO2 , CO FE is kept at 90.1% at -0.5 V versus RHE. During gas phase flow electrolysis using simulated flue gas, the CO partial current density is further increased to 86.4 mA cm-2 and CO FE reached >90% at the cell voltage of 3.4 V. Experiments and density functional theory calculations indicate that uniform single-atom Co-N4 sites mainly contribute to the high activity for CO2 reduction.