Ferromagnetic single-atom spin catalyst for boosting water splitting.

Heterogeneous single-atom spin catalysts combined with magnetic fields provide a powerful means for accelerating chemical reactions with enhanced metal utilization and reaction efficiency. However, designing these catalysts remains challenging due to the need for a high density of atomically dispersed active sites with a short-range quantum spin exchange interaction and long-range ferromagnetic ordering. Here, we devised a scalable hydrothermal approach involving an operando acidic environment for synthesizing various single-atom spin catalysts with widely tunable substitutional magnetic atoms (M1) in a MoS2 host. Among all the M1/MoS2 species, Ni1/MoS2 adopts a distorted tetragonal structure that prompts both ferromagnetic coupling to nearby S atoms as well as adjacent Ni1 sites, resulting in global room-temperature ferromagnetism. Such coupling benefits spin-selective charge transfer in oxygen evolution reactions to produce triplet O2. Furthermore, a mild magnetic field of ~0.5 T enhances the oxygen evolution reaction magnetocurrent by ~2,880% over Ni1/MoS2, leading to excellent activity and stability in both seawater and pure water splitting cells. As supported by operando characterizations and theoretical calculations, a great magnetic-field-enhanced oxygen evolution reaction performance over Ni1/MoS2 is attributed to a field-induced spin alignment and spin density optimization over S active sites arising from field-regulated S(p)-Ni(d) hybridization, which in turn optimizes the adsorption energies for radical intermediates to reduce overall reaction barriers.

Catalytically active atomically thin cuprate with periodic Cu single sites.

Rational design and synthesis of catalytically active two-dimensional (2D) materials with an abundance of atomically precise active sites in their basal planes remains a great challenge. Here, we report a ligand exchange strategy to exfoliate bulk [Cu4(OH)6][O3S(CH2)4SO3] cuprate crystals into atomically thin 2D cuprate layers ([Cu2(OH)3]+). The basal plane of 2D cuprate layers contains periodic arrays of accessible unsaturated Cu(II) single sites (2D-CuSSs), which are found to promote efficient oxidative Chan-Lam coupling. Our mechanistic studies reveal that the reactions proceed via coordinatively unsaturated CuO4(II) single sites with the formation of Cu(I) species in the rate-limiting step, as corroborated by both operando experimental and theoretical studies. The robust stability of 2D-CuSSs in both batch and continuous flow reactions, coupled with their recyclability and good performance in complex molecule derivatization, render 2D-CuSSs attractive catalyst candidates for broad utility in fine chemical synthesis.

Degradation Chemistry and Kinetic Stabilization of Magnetic CrI3.

The discovery of the intrinsic magnetic order in single-layer chromium trihalides (CrX3, X = I, Br, and Cl) has drawn intensive interest due to their potential application in spintronic devices. However, the notorious environmental instability of this class of materials under ambient conditions renders their device fabrication and practical application extremely challenging. Here, we performed a systematic investigation of the degradation chemistry of chromium iodide (CrI3), the most studied among CrX3 families, via a joint spectroscopic and microscopic analysis of the structural and composition evolution of bulk and exfoliated nanoflakes in different environments. Unlike other air-sensitive 2D materials, CrI3 undergoes a pseudo-first-order hydrolysis in the presence of pure water toward the formation of amorphous Cr(OH)3 and hydrogen iodide (HI) with a rate constant of kI = 0.63 day-1 without light. In contrast, a faster pseudo-first-order surface oxidation of CrI3 occurs in a pure O2 environment, generating CrO3 and I2 with a large rate constant of kCr = 4.2 day-1. Both hydrolysis and surface oxidation of CrI3 can be accelerated via light irradiation, resulting in its ultrafast degradation in air. The new chemical insights obtained allow for the design of an effective stabilization strategy for CrI3 with preserved optical and magnetic properties. The use of organic acid solvents (e.g., formic acid) as reversible capping agents ensures that CrI3 nanoflakes remain stable beyond 1 month due to the effective suppression of both hydrolysis and oxidation of CrI3.

Scalable two-step annealing method for preparing ultra-high-density single-atom catalyst libraries.

The stabilization of transition metals as isolated centres with high areal density on suitably tailored carriers is crucial for maximizing the industrial potential of single-atom heterogeneous catalysts. However, achieving single-atom dispersions at metal contents above 2 wt% remains challenging. Here we introduce a versatile approach combining impregnation and two-step annealing to synthesize ultra-high-density single-atom catalysts with metal contents up to 23 wt% for 15 metals on chemically distinct carriers. Translation to a standardized, automated protocol demonstrates the robustness of our method and provides a path to explore virtually unlimited libraries of mono- or multimetallic catalysts. At the molecular level, characterization of the synthesis mechanism through experiments and simulations shows that controlling the bonding of metal precursors with the carrier via stepwise ligand removal prevents their thermally induced aggregation into nanoparticles. The drastically enhanced reactivity with increasing metal content exemplifies the need to optimize the surface metal density for a given application. Moreover, the loading-dependent site-specific activity observed in three distinct catalytic systems reflects the well-known complexity in heterogeneous catalyst design, which now can be tackled with a library of single-atom catalysts with widely tunable metal loadings.

Facile Production of Phosphorene Nanoribbons towards Application in Lithium Metal Battery.

Like phosphorene, phosphorene nanoribbon (PNR) promises exotic properties but unzipping phosphorene into edge-defined PNR is non-trivial because of uncontrolled cutting of phosphorene along random directions. Here a facile electrochemical strategy to fabricate zigzag-edged PNRs in high yield (>80%) is reported. The presence of chemically active zigzag edges in PNR allows it to spontaneously react with Li to form a Li+ ion conducting Li3 P phase, which can be used as a protective layer on Li metal anode in lithium metal batteries (LMBs). PNR protective layer prevents the parasitic reaction between lithium metal and electrolyte and promotes Li+ ion diffusion kinetics, enabling homogenous Li+ ion flux and long-time cycling stability up to 1100 h at a current density of 1 mA cm-2 . LiFePO4 |PNR-Li full-cell batteries with an areal capacity of 2 mAh cm-2 , a lean electrolyte (20 µl mAh-1 ) and a negative/positive (N/P) electrodes ratio of 3.5 can be stably cycled over 100 cycles.

Zero-Valent Palladium Single-Atoms Catalysts Confined in Black Phosphorus for Efficient Semi-Hydrogenation.

Single-atom catalysts (SACs) represent a new frontier in heterogeneous catalysis due to their remarkable catalytic properties and maximized atomic utilization. However, single atoms often bond to the support with polarized electron density and thus exhibit a high valence state, limiting their catalytic scopes in many chemical transformations. Here, it is demonstrated that 2D black phosphorus (BP) acts as giant phosphorus (P) ligand to confine a high density of single atoms (e.g., Pd1 , Pt1 ) via atomic layer deposition. Unlike other 2D materials, BP with relatively low electronegativity and buckled structure favors the strong confinement of robust zero-valent palladium SACs in the vacancy site. Metallic Pd1 /BP SAC shows a highly selective semi-hydrogenation of phenylacetylene toward styrene, distinct from metallic Pd nanoparticles that facilitate the formation of fully hydrogenated products. Density functional theory calculations reveal that Pd atom forms covalent-like bonding with adjacent P atoms, wherein H atoms tend to adsorb, aiding the dissociative adsorption of H2 . Zero-valent Pd in the confined space favors a larger energy gain for the synthesis of partially hydrogenated product over the fully hydrogenated one. This work provides a new route toward the synthesis of zero-valent SACs on BP for organic transformations.

Ordered clustering of single atomic Te vacancies in atomically thin PtTe2 promotes hydrogen evolution catalysis.

Exposing and stabilizing undercoordinated platinum (Pt) sites and therefore optimizing their adsorption to reactive intermediates offers a desirable strategy to develop highly efficient Pt-based electrocatalysts. However, preparation of atomically controllable Pt-based model catalysts to understand the correlation between electronic structure, adsorption energy, and catalytic properties of atomic Pt sites is still challenging. Herein we report the atomically thin two-dimensional PtTe2 nanosheets with well-dispersed single atomic Te vacancies (Te-SAVs) and atomically well-defined undercoordinated Pt sites as a model electrocatalyst. A controlled thermal treatment drives the migration of the Te-SAVs to form thermodynamically stabilized, ordered Te-SAV clusters, which decreases both the density of states of undercoordinated Pt sites around the Fermi level and the interacting orbital volume of Pt sites. As a result, the binding strength of atomically defined Pt active sites to H intermediates is effectively reduced, which renders PtTe2 nanosheets highly active and stable in hydrogen evolution reaction.

Dense-Stacking Porous Conjugated Polymer as Reactive-Type Host for High-Performance Lithium Sulfur Batteries.

Commercialization of the lithium-sulfur battery is hampered by bottlenecks like low sulfur loading, high cathode porosity, uncontrollable Li2 Sx deposition and sluggish kinetics of Li2 S activation. Herein, we developed a densely stacked redox-active hexaazatrinaphthylene (HATN) polymer with a surface area of 302 m2 g-1 and a very high bulk density of ca. 1.60 g cm-3 . Uniquely, HATN polymer has a similar redox potential window to S, which facilitates the binding of Li2 Sx and its transformation chemistry within the bulky polymer host, leading to fast Li2 S/S kinetics. The compact polymer/S electrode presents a high sulfur loading of ca. 15 mgs cm-2 (200-µm thickness) with a low cathode porosity of 41 %. It delivers a high areal capacity of ca. 14 mAh cm-2 and good cycling stability (200 cycles) at electrolyte-sulfur (E/S) ratio of 5 µL mgs -1 . The assembled pouch cell delivers a cell-level high energy density of 303 Wh kg-1 and 392 Wh L-1 .

Tuning the Spin Density of Cobalt Single-Atom Catalysts for Efficient Oxygen Evolution.

Single-atom catalysts (SACs) with magnetic elements as the active center have been widely exploited for efficient electrochemical conversions. Understanding the catalytic role of spin, and thus modulating the spin density of a single-atom center, is of profound fundamental interest and technological impact. Here, we synthesized ferromagnetic single Co atom catalysts on TaS2 monolayers (Co1/TaS2) as a model system to explore the spin-activity correlation for the oxygen evolution reaction (OER). A single Co atom adsorbed at the hollow site (CoHS) with spin-polarized electronic states serves as the active site for OER, whose spin density can be regulated by its neighboring single Co site via tuning the Co loading. Both experimental and theoretical results reveal the spin density-dependent OER activity that an optimal spin density of CoHS can be achieved with a neighboring hetero-single CoTa site (substitution of Ta by Co) for a superior OER performance, in contrast to a homo-single CoHS site, which creates an excessive spin density over vicinal CoHS. An optimized spin density of CoHS results in an optimal binding energy of oxygen species for the OER. Establishing the spin-activity correlation in SACs may create a descriptor for designing efficient magnetic SACs for renewable energy conversions.

Electrochemically Exfoliated Platinum Dichalcogenide Atomic Layers for High-Performance Air-Stable Infrared Photodetectors.

Platinum dichalcogenide (PtX2), an emergent group-10 transition metal dichalcogenide (TMD) has shown great potential in infrared photonic and optoelectronic applications due to its layer-dependent electronic structure with potentially suitable bandgap. However, a scalable synthesis of PtSe2 and PtTe2 atomic layers with controlled thickness still represents a major challenge in this field because of the strong interlayer interactions. Herein, we develop a facile cathodic exfoliation approach for the synthesis of solution-processable high-quality PtSe2 and PtTe2 atomic layers for high-performance infrared (IR) photodetection. As-exfoliated PtSe2 and PtTe2 bilayer exhibit an excellent photoresponsivity of 72 and 1620 mA W-1 at zero gate voltage under a 1540 nm laser illumination, respectively, approximately several orders of magnitude higher than that of the majority of IR photodetectors based on graphene, TMDs, and black phosphorus. In addition, our PtSe2 and PtTe2 bilayer device also shows a decent specific detectivity of beyond 109 Jones with remarkable air-stability (>several months), outperforming the mechanically exfoliated counterparts under the laser illumination with a similar wavelength. Moreover, a high yield of PtSe2 and PtTe2 atomic layers dispersed in solution also allows for a facile fabrication of air-stable wafer-scale IR photodetector. This work demonstrates a new route for the synthesis of solution-processable layered materials with the narrow bandgap for the infrared optoelectronic applications.

Printable two-dimensional superconducting monolayers.

Two-dimensional superconductor (2DSC) monolayers with non-centrosymmetry exhibit unconventional Ising pair superconductivity and an enhanced upper critical field beyond the Pauli paramagnetic limit, driving intense research interest. However, they are often susceptible to structural disorder and environmental oxidation, which destroy electronic coherence and provide technical challenges in the creation of artificial van der Waals heterostructures (vdWHs) for devices. Herein, we report a general and scalable synthesis of highly crystalline 2DSC monolayers via a mild electrochemical exfoliation method using flexible organic ammonium cations solvated with neutral solvent molecules as co-intercalants. Using NbSe2 as a model system, we achieved a high yield (>75%) of large-sized single-crystal monolayers up to 300 µm. The as-fabricated, twisted NbSe2 vdWHs demonstrate high stability, good interfacial properties and a critical current that is modulated by magnetic field when one flux quantum fits to an integer number of moiré cells. Additionally, formulated 2DSC inks can be exploited to fabricate wafer-scale 2D superconducting wire arrays and three-dimensional superconducting composites with desirable morphologies.

Atomically-precise dopant-controlled single cluster catalysis for electrochemical nitrogen reduction.

The ability to precisely engineer the doping of sub-nanometer bimetallic clusters offers exciting opportunities for tailoring their catalytic performance with atomic accuracy. However, the fabrication of singly dispersed bimetallic cluster catalysts with atomic-level control of dopants has been a long-standing challenge. Herein, we report a strategy for the controllable synthesis of a precisely doped single cluster catalyst consisting of partially ligand-enveloped Au4Pt2 clusters supported on defective graphene. This creates a bimetal single cluster catalyst (Au4Pt2/G) with exceptional activity for electrochemical nitrogen (N2) reduction. Our mechanistic study reveals that each N2 molecule is activated in the confined region between cluster and graphene. The heteroatom dopant plays an indispensable role in the activation of N2 via an enhanced back donation of electrons to the N2 LUMO. Moreover, besides the heteroatom Pt, the catalytic performance of single cluster catalyst can be further tuned by using Pd in place of Pt as the dopant.

Imprinting Ferromagnetism and Superconductivity in Single Atomic Layers of Molecular Superlattices.

Ferromagnetism and superconductivity are two antagonistic phenomena since ferromagnetic exchange fields tend to destroy singlet Cooper pairs. Reconciliation of these two competing phases has been achieved in vertically stacked heterostructures where these two orders are confined in different layers. However, controllable integration of these two phases in one atomic layer is a longstanding challenge. Here, an interlayer-space-confined chemical design (ICCD) is reported for the synthesis of dilute single-atom-doped TaS2 molecular superlattice, whereby ferromagnetism is observed in the superconducting TaS2 layers. The intercalation of 2H-TaS2 crystal with bulky organic ammonium molecule expands its van der Waals gap for single-atom doping via co-intercalated cobalt ions, resulting in the formation of quasi-monolayer Co-doped TaS2 superlattices. Isolated Co atoms are decorated in the basal plane of the TaS2 via substituting the Ta atom or anchoring at a hollow site, wherein the orbital-selected p-d hybridization between Co and neighboring Ta and S atoms induces local magnetic moments with strong ferromagnetic coupling. This ICCD approach can be applied to various metal ions, enabling the synthesis of a series of crystal-size TaS2 molecular superlattices.

A Graphene-Supported Single-Atom FeN5 Catalytic Site for Efficient Electrochemical CO2 Reduction.

Electrochemical conversion of CO2 into valued products is one of the most important issues but remains a great challenge in chemistry. Herein, we report a novel synthetic approach involving prolonged thermal pyrolysis of hemin and melamine molecules on graphene for the fabrication of a robust and efficient single-iron-atom electrocatalyst for electrochemical CO2 reduction. The single-atom catalyst exhibits high Faradaic efficiency (ca. 97.0 %) for CO production at a low overpotential of 0.35 V, outperforming all Fe-N-C-based catalysts. The remarkable performance for CO2 -to-CO conversion can be attributed to the presence of highly efficient singly dispersed FeN5 active sites supported on N-doped graphene with an additional axial ligand coordinated to FeN4 . DFT calculations revealed that the axial pyrrolic nitrogen ligand of the FeN5 site further depletes the electron density of Fe 3d orbitals and thus reduces the Fe-CO π back-donation, thus enabling the rapid desorption of CO and high selectivity for CO production.

One-Pot Synthesis of BiCuSO Nanosheets under Ambient Atmosphere as Broadband Spectrum Photocatalyst.

Cuprous based chalcogenides have attracted intensive research interest due to the potential applications in solar energy conversion. However, typical fabrications of these compounds are often carried out under severe conditions, such as inert gas protection, high vacuum, and/or extreme high temperature. Here we reported a one-pot process for cuprous based chalcogenides synthesis in aqueous solution. A strategy for BiCuSO nanosheets fabrication without toxic chemicals or rigorous reagents at pretty low temperatures under an ambient atmosphere was established, with the practicality of morphology controlling and the compatibility of multifarious precursors. Platelike BiCuSO with a thickness range from several to hundreds nanometers are fabricated by adjusting the alkali concentration, reaction time, and temperature. The positive effect of alkali hydroxide concentration is proposed cautiously based on the experimental results. The photocatalytic activities of BiCuSO nanosheet under UV, visible, and near-infrared irradiation were also investigated. BiCuSO obtained at room temperature with a thickness of 4.5 nm showed the most impressive efficiency to decompose organic contaminants. Our research presented a new way for cuprous sulfides fabrication, and might open up a new vista for large-scale synthesis of cuprous based materials as promising broadband spectrum light-absorbing materials.

Synthesis and Broadband Spectra Photocatalytic Properties of Bi2O2(CO3)1-xSx.

High efficiency photocatalyst Bi2O2(CO3)1-xSx was synthesized conveniently with chemical bath precipitation using Bi2O2CO3 as the precursor. The microstructures of the samples are systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and UV-Vis spectroscopy; the optical and photocatalytic properties are carefully tested as well. The content of S, which was tuned through the controlling of the precipitation process, was verified to have an intense effect over the photocatalytic properties. A nearly saturated S ratio and the best photocatalytic performance were observed in specimens with the most S content. Our study reveals that, with negligible influence of the morphology and crystal structure, Bi2O2(CO3)1-xSx possessed a broadened optical absorption regionfromultraviolet to visible light, and enhanced photocatalytic activity in comparison to precursor Bi2O2CO3 in photocatalytic degradation of Congo Red aqueous solution.

Highly (001)-Textured Tetragonal BiFeO3 Film and Its Photoelectrochemical Behaviors Tuned by Magnetic Field.

Highly (001)-textured BiFeO3 film in tetragonal phase (T-BFO) with a giant c/a ratio was first obtained on quartz/polycrystalline ITO substrate. Our results indicate that the polycrystalline ITO layer with small surface roughness is a critical point to control the growth of T-BFO structure. It should be ascribed to the fact that a Bi-rich phase interlayer (∼5 nm) could be formed on ITO, which acted as a crystal seed layer and thus induced the growth of (001)-textured T-BFO structure. The observed weak room temperature ferromagnetism should be attributed to Fe valence change. Open circuit potential measurements under 360 µW/cm2 full spectra irradiation show that the open circuit potential and the lifetime of photo-induced carriers increased under applied magnetic field, which reveals that the applied magnetic field can manipulate the photo electrochemical behaviors of BFO film. Our findings offer a simple way to fabricate highly (001)-textured T-BFO film, which make it desirable to obtain extensive applications for these oriented BFO films.

Highly selective and active CO2 reduction electrocatalysts based on cobalt phthalocyanine/carbon nanotube hybrid structures.

Electrochemical reduction of carbon dioxide with renewable energy is a sustainable way of producing carbon-neutral fuels. However, developing active, selective and stable electrocatalysts is challenging and entails material structure design and tailoring across a range of length scales. Here we report a cobalt-phthalocyanine-based high-performance carbon dioxide reduction electrocatalyst material developed with a combined nanoscale and molecular approach. On the nanoscale, cobalt phthalocyanine (CoPc) molecules are uniformly anchored on carbon nanotubes to afford substantially increased current density, improved selectivity for carbon monoxide, and enhanced durability. On the molecular level, the catalytic performance is further enhanced by introducing cyano groups to the CoPc molecule. The resulting hybrid catalyst exhibits >95% Faradaic efficiency for carbon monoxide production in a wide potential range and extraordinary catalytic activity with a current density of 15.0 mA cm-2 and a turnover frequency of 4.1 s-1 at the overpotential of 0.52 V in a near-neutral aqueous solution.

Bi(1-x)La(x)CuSeO as New Tunable Full Solar Light Active Photocatalysts.

Photocatalysis is attracting enormous interest driven by the great promise of addressing current energy and environmental crises by converting solar light directly into chemical energy. However, efficiently harvesting solar energy for photocatalysis remains a pressing challenge, and the charge kinetics and mechanism of the photocatalytic process is far from being well understood. Here we report a new full solar spectrum driven photocatalyst in the system of a layered oxyselenide BiCuSeO with good photocatalytic activity for degradation of organic pollutants and chemical stability under light irradiation, and the photocatalytic performance of BiCuSeO can be further improved by band gap engineering with introduction of La. Our measurements and density-functional-theory calculations reveal that the effective mass and mobility of the carriers in BiCuSeO can be tuned by the La-doping, which are responsible for the tunable photocatalytic activity. Our findings may offer new perspectives for understanding the mechanism of photocatalysis through modulating the charge mobility and the effective mass of carriers and provide a guidance for designing efficient photocatalyts.